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Sol-gel immobilized cyano-polydimethylsiloxane and short chain polyethylene glycol coatings for capillary microextractio...

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Title:
Sol-gel immobilized cyano-polydimethylsiloxane and short chain polyethylene glycol coatings for capillary microextraction coupled to gas chromatography
Physical Description:
Book
Language:
English
Creator:
Kulkarni, Sameer M
Publisher:
University of South Florida
Place of Publication:
Tampa, Fla.
Publication Date:

Subjects

Subjects / Keywords:
SPME
In-tube SPME
Polar
PAHs
Ketones
Aldehydes
Amines
Phenols
Fatty acids
Dissertations, Academic -- Chemistry -- Doctoral -- USF   ( lcsh )
Genre:
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
ABSTRACT: Two highly polar sol-gel coatings were developed for capillary microextraction (CME). One of the coatings contained cyanopropyl-polydimethylsiloxane (CN-PDMS) and the other low molecular weight polyethylene glycol. These highly polar coatings were immobilized via sol-gel chemistry allowing for direct chemical bonding to the inner surface of fused silica capillaries. These sol-gel coated microextraction capillaries were employed in CME for solvent-free microextraction and preconcentration of trace analytes (polar, moderately polar, and nonpolar) from aqueous matrices. CN-PDMS and short chain PEG extraction phases exhibit both polar and polarizable characteristics. Therefore, both sol-gel CN-PDMS and short chain sol-gel PEG coatings were able to extract analytes of different polarity from aqueous media.Both sol-gel CN-PDMS and sol-gel PEG coatings provided effective extraction of polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures commonly used in SPME experiments with conventional coatings. For each of these coatings, detection limits on the order of nanogram/liter (ng/L) were achieved for both polar and nonpolar analytes extracted simultaneously from aqueous media followed by GC-FID analysis. Both sol-gel CN-PDMS and short chain sol-gel PEG coated microextraction capillaries showed excellent run-to-run and capillary-to-capillary extraction reproducibility (GC peak area RSD < 6% & 5%, respectively) for nonpolar as well as polar analytes. For the sol-gel CN-PDMS coatings, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, for the extraction of polar and nonpolar organic analytes, respectively.Similarly, the sol-gel PEG coatings used for the extraction of polar organic analytes survived a conditioning temperature of 340 degrees C. Both sol-gel CN-PDMS and sol-gel PEG coated microextraction capillaries showed no significant changes in the peak areas of the extracted analytes even after being washed with organic solvents (dichloromethane and methanol (1:1), v/v) for 24 hours. The excellent thermal and solvent stabilities can be attributed to the presence of chemical bonds between the sol-gel coatings and the fused silica surface.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2007.
Bibliography:
Includes bibliographical references.
System Details:
System requirements: World Wide Web browser and PDF reader.
System Details:
Mode of access: World Wide Web.
Statement of Responsibility:
by Sameer M. Kulkarni.
General Note:
Title from PDF of title page.
General Note:
Document formatted into pages; contains 288 pages.
General Note:
Includes vita.

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University of South Florida Library
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University of South Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 001919656
oclc - 184941078
usfldc doi - E14-SFE0002083
usfldc handle - e14.2083
System ID:
SFS0026401:00001


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Sol-gel immobilized cyano-polydimethylsiloxane and short chain polyethylene glycol coatings for capillary microextraction coupled to gas chromatography
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ABSTRACT: Two highly polar sol-gel coatings were developed for capillary microextraction (CME). One of the coatings contained cyanopropyl-polydimethylsiloxane (CN-PDMS) and the other low molecular weight polyethylene glycol. These highly polar coatings were immobilized via sol-gel chemistry allowing for direct chemical bonding to the inner surface of fused silica capillaries. These sol-gel coated microextraction capillaries were employed in CME for solvent-free microextraction and preconcentration of trace analytes (polar, moderately polar, and nonpolar) from aqueous matrices. CN-PDMS and short chain PEG extraction phases exhibit both polar and polarizable characteristics. Therefore, both sol-gel CN-PDMS and short chain sol-gel PEG coatings were able to extract analytes of different polarity from aqueous media.Both sol-gel CN-PDMS and sol-gel PEG coatings provided effective extraction of polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures commonly used in SPME experiments with conventional coatings. For each of these coatings, detection limits on the order of nanogram/liter (ng/L) were achieved for both polar and nonpolar analytes extracted simultaneously from aqueous media followed by GC-FID analysis. Both sol-gel CN-PDMS and short chain sol-gel PEG coated microextraction capillaries showed excellent run-to-run and capillary-to-capillary extraction reproducibility (GC peak area RSD < 6% & 5%, respectively) for nonpolar as well as polar analytes. For the sol-gel CN-PDMS coatings, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, for the extraction of polar and nonpolar organic analytes, respectively.Similarly, the sol-gel PEG coatings used for the extraction of polar organic analytes survived a conditioning temperature of 340 degrees C. Both sol-gel CN-PDMS and sol-gel PEG coated microextraction capillaries showed no significant changes in the peak areas of the extracted analytes even after being washed with organic solvents (dichloromethane and methanol (1:1), v/v) for 24 hours. The excellent thermal and solvent stabilities can be attributed to the presence of chemical bonds between the sol-gel coatings and the fused silica surface.
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SPME.
In-tube SPME.
Polar.
PAHs.
Ketones.
Aldehydes.
Amines.
Phenols.
Fatty acids.
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Sol-Gel Immobilized Cyano-Polydimethylsilo xane and Short Chain Polyethylene Glycol Coatings for Capillary Microextraction Coupled to Gas Chromatography by Sameer M. Kulkarni A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Chemistry College of Arts and Sciences University of South Florida Major Professor: Abdul Malik, Ph.D. Milton D. Johnston, Jr., Ph.D. Robert Potter, Ph.D. Jennifer Lewis, Ph.D. Date of Approval: July 16, 2007 Keywords: SPME, In-tube SPME, polar, PAHs ketones, aldehydes, amines, phenols, fatty acids Copyright 2007, Sameer M. Kulkarni

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DEDICATION To my parents Mohan and Meenal Kulkarni, my wife Pooja Kulkarni, my brother Robin Kulkarni, who made this possible, for their over whelming love, encouragement, and support.

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ACKNOWLEDGMENTS I would like to acknowledge many pe ople for their support, guidance, and encouragement during my doctoral work. I woul d like to thank my ma jor professor, Dr. Abdul Malik, for his guidance, encouragement, and patience. I am also very grateful to my dissertation committee members: Dr. Jennife r Lewis; Dr. Milton D. Johnston, Jr.; and Dr. Robert Potter for their valuab le advice, and encouragement. I would like to thank all my former and current colleagues, Dr. Khalid Alhooshani, Dr. Tae-Young Kim, Dr. Wen Li, Li Fang, A nne Marie Shearrow, Erica Turner, and Scott Segro for their continuous assist ance, encouragement, and friendship. I acknowledge the Department of Chemistry fo r their financial s upport throughout my graduate study. Finally, I would like to express my great ap preciation and gratitude to my parents, my wife, and my brother for their immense love and support.

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i TABLE OF CONTENTS LIST OF TABLES viii LIST OF FIGURES xiv LIST OF SCHEMES xviii LIST OF SYMBOLS AND ABBREVIATIONS xix ABSTRACT xxiii CHAPTER 1: AN INTRODUCTION TO SOLID-PHASE MICROEXTRACTION 1 1.1 An Overview on Sample Preparation 1 1.2 History of SPME 3 1.3 Extraction Modes in SPME 8 1.3.1 Modes of Extraction with Coated SPME Fiber 8 1.3.2 Modes of Extraction with in-tube SPME 14 1.4 Coatings used in SPME and in-tube SPME 15 1.4.1 Coatings used in Fiber SPME 15 1.4.1.1 Commercially Available Coatings for Fiber SPME 16 1.4.1.2 Tailor-made Coatings for Fiber SPME 19 1.4.1.2.1 Carbonaceous Sorbents 19 1.4.1.2.2 Bonded-phase Silica Sorbents 20 1.4.1.2.3 Coated Metallic SPME Fibers 21 1.4.1.2.4 Miscellaneous Sorbents 23 1.4.2 Coatings used in in-tube SPME 26 1.4.2.1 Commercial GC Sorben ts as in-tube SPME Coatings 27

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ii 1.4.2.2 Tailor-made Coatings for in-tube SPME 31 1.4.2.2.1 Restricted Access Materials 31 1.4.2.2.2 Molecularly Imprinted Polymers 32 1.4.2.2.3 Monolithic Sorbents 34 1.4.2.2.4 Miscellaneous Sorbents 37 1.5 Parameters Affecting Extraction E fficiency 38 1.5.1 Adjustment of Sample Matrix pH 39 1.5.2 Agitation of Sample Matrix 39 1.5.3 Heating of Sample Matrix 40 1.5.4 Addition of Salt to Sample Matrix 42 1.6 Derivatization 42 1.7 References to Chapter 1 45 CHAPTER 2: SOL-GEL TECHNOLOGY IN SOLID PHASE MICROEXTRACTION AND CAPILLARY MIRCOEXTRACTION 54 2.1 Sol-gel Technology: A brief history 54 2.2 Reactions involved in sol-gel process 56 2.3 Steps involved in Preparation of Sol-gel Soated SPME Fiber and CME Capillary 63 2.3.1 Design and Preparation of Sol Solution 63 2.3.2 Pretreatment, Coating, and Post-coating Treatment of Fused Silica SPME Fiber/Capillary 64 2.4 Characterization and Morphol ogy of Sol-gel Sorbents 69 2.5 Sol-gel Sorbents in SPME and CME: A Brief Overview 71 2.5.1 Sol-gel PDMS and PDMDPS Sorbents 77 2.5.2 Sol-gel PDMS-PVA Sorbents 78 2.5.3 Sol-gel PDMS-PMPVS Sorbents 79 2.5.4 Sol-gel PDMS-DVB Sorbents 80 2.5.5 Sol-gel PDMS-Fullerene Sorbent 81 2.5.6 Sol-gel PDMS-Calix{4}arene Sorbents 82

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iii 2.5.7 Sol-gel PDMS-Crown ether Sorbents 85 2.5.8 Sol-gel Cyclodextrin Sorbents 90 2.5.9 Sol-gel Dendrimer Sorbent 91 2.5.10 Sol-gel Poly-THF Sorbent 92 2.5.11 Miscellaneous Sol-gel Sorbents 93 2.6 References to Chapter 2 96 CHAPTER 3: SOL-GEL IMMOBILIZED CYANOPOLYDIMETHYLSILOXANE COATING FOR CAPILLARY MICROEXTRACTION 104 3.1 Introduction 104 3.2 Experimental Section 107 3.2.1 Equipment 107 3.2.2 Materials and Chemicals 108 3.2.3 Preparation of Sol-gel CN-PDMS Coated Microextraction Capillaries 110 3.2.3.1 Preparation of Sol Solution 110 3.2.3.2 Pretreatment of Fused Silica Capillary 112 3.2.3.3 Coating of Fused Sili ca Capillary with Sol Solution 113 3.2.3.4 Post-coating Treatment 114 3.2.4 Preparation of Standard Solution Samples for CME 115 3.2.5 Capillary Microextraction of Analytes on Sol-gel CN-PDMS Coated Capillaries 115 3.2.6 GC Analysis of the Extracted Analytes 115 3.2.7 Calculation of limit of Detection (LOD) for the Extracted Analytes 116 3.2.8 Analyte Enhancement Factor for Sol-gel CN-PDMS Coated Microextraction Capillaries 118

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iv 3.3 Resuts and Discussion 121 3.3.1 Reactions Leading to the Formation of Chemically Immobilized Sol-gel CN-PDMS Network 121 3.3.2 Characterization of surface morphology and Determination of Coating Thickness using Scanning Electron Microscopy 128 3.3.3 Thermaland Solvent Stabilities of Sol-gel CN-PDMS Coated Micorextraction Capillaries 128 3.3.4 Extraction Profile of Moderately Polar and Highly Polar Organic Compounds on Sol-gel CN-PDMS Microextraction Capillary 135 3.3.5 CME-GC Analysis of Nonpolar, Moderately Polar, and Highly Polar Organic Compounds using Sol-gel CN-PDMS Coated Microextraction Capillaries 135 3.3.5.1 CME-GC-FID of Polycyclic Aromatic Hydrocarbons using Sol-gel CN-PDMS Coated Microextraction Capillaries 137 3.3.5.2 CME-GC-FID of Aldehydes and Ketones using Sol-gel CN-PDMS Coated Microextraction Capillaries 144 3.3.5.3 CME-GC-FID of Aromatic Amines using Sol-gel CN-PDMS Coated Microextraction Capillaries 156 3.3.5.4 CME-GC-FID of Chlorophenols using Sol-gel CN-PDMS Coated Microextraction Capillaries 162 3.3.5.5 CME-GC-FID of Alcohols using Sol-gel CNPDMS Coated Microextraction Capillaries 168 3.3.5.6 CME-GC-FID of Free Fatty Acids using Sol-gel CN-PDMS Coated Microextraction Capillaries 174

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v 3.3.5.7 CME-GC-FID of Mixture of Nonpolar, Moderately Polar, and Highly Polar Organic Compounds using Sol-gel CN-PDMS Coated Microextraction Capillary 180 3.3.5.8 Performance of Sol-gel CN-PDMS Capillary in CME 180 3.4 Conclusion 184 3.5 References to Chapter 3 185 CHAPTER 4: SOL-GEL I MMOBILIZED SHORT CHAIN POLYETHYLENE GLYCOL COATING FOR CAPILLARY MICROEXTRACTION 189 4.1 Introduction 189 4.2 Experimental Section 191 4.2.1 Equipment 191 4.2.2 Materials and Chemicals 191 4.2.3 Preparation of Sol-gel PEG Coated Microextraction Capillaries 192 4.2.3.1 Preparation of Sol Solution 193 4.2.3.2 Pretreatment of Fused Silica Capillary 193 4.2.3.3 Coating of Fused Silica Capillary with Sol Solution 195 4.2.3.4 Post-coating Treatment 196 4.2.4 Preparation of Standard Solution Samples for CME 197 4.2.5 Capillary Microextraction of Analytes on Sol-gel PEG Coated Capillaries 197 4.2.6 GC Analysis of the Extracted Analytes 198 4.2.7 Calculation of the Limit of Detection (LOD) for Extracted Analytes 199

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vi 4.2.8 Analyte Enhancement Factor for Short Chain Sol-gel PEG Coated Microextract ion Capillaries 199 4.3 Results and Discussion 199 4.3.1 Reactions Leading to the Formation of a Chemically Immobilized Sol-gel PEG Network 200 4.3.2 Determination of the Coating Thickness of the Solgel Coating using Scanni ng Electron Microscopy 201 4.3.3 Thermaland Solvent Stabilities of Sol-gel PEG Coating 206 4.3.4 Extraction Profile of Organic Compounds on Sol-gel PEG Coated Microextraction Capillary 209 4.3.5 CME-GC Analysis of Moderately Polar and Highly Polar Organic Compounds using Sol-gel PEG Microextraction Capillaries 209 4.3.5.1 CME-GC-FID of Aldehydes and Ketones using Sol-gel PEG Coated Microextraction Capillaries 211 4.3.5.2 CME-GC-FID of Aromatic Amines using Sol-gel PEG Coated Microextraction Capillaries 223 4.3.5.3 CME-GC-FID of Phenol Derivatives using Sol-gel PEG Coated Microextraction Capillaries 231 4.3.5.4 CME-GC-FID of Alcohols using Sol-gel PEG Coated Microextraction Capillaries 238 4.3.5.5 CME-GC-FID of Free Fatty Acids using Sol-gel PEG Coated Microextraction Capillaries 244

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vii 4.3.5.6 CME-GC-FID of Mixture of Moderately Polar and Highly Polar Organic Compounds using Sol-gel PEG Coated Microextraction Capillaries 251 4.3.5.7 CME Performance of Sol-gel Capillaries Prepared with and without TESP 251 4.4 Conclusion 255 4.5 References to Chapter 4 256 APPENDICES 260 Appendix A: Sol-gel Immobilized Cyano-polydimethylsiloxane Coating for Capillary Microextraction of Aqueous Trace Analytes Ranging from Polycyclic Aromatic Hydrocarbons to Free Fatty Acids 261 Appendix B: Quantitative Analysis in CME 273 Appendix C: Optimization of Sol-gel Coatings Solution Composition 278 Appendix D: LOD data for various or ganic analytes extracted using sol-gel CN-PDMS, short chain sol-gel PEG and other SPME/CME coatings reported in literature 280 ABOUT THE AUTHOR End Page

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viii LIST OF TABLES Table 1.1 Commercially available fiber coatings for SPME and its applications 17 Table 1.2 Chemical structure and compos ition of GC stationary phases used in in-tube SPME 28 Table 2.1 Characteristic Infrared bands in spectra of sol-gel materials 70 Table 2.2 Summary of sol-gel so rbent used in SPME and CME 72 Table 3.1 Names, functions, and chemi cal structures of sol-gel CN-PDMS coating solution ingredients 111 Table 3.2 GC Peak area repeatabilit y data (n=3) for free fatty acids obtained in CME-GC experiments before and after rinsing the sol-gel CN-PDMS coated microe xtraction capillary with a mixture (50 mL) of dichloromethane/methanol (1:1, v/v) for 24 hours 134 Table 3.3 Chemical structures and pertinent physical properties of polycyclic aromatic hydrocarbons (PAHs) extracted using solgel CN-PDMS coating 139 Table 3.4 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of PAHs extracted on a sol-ge l CN-PDMS microextraction capillary 141 Table 3.5 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for a mixtures of PAHs extracted on a sol-gel CN-PDMS microextraction capillary 142 Table 3.6 Limits of detection (LOD) da ta for PAHs in CME-GC-FID using sol-gel CN-PDMS microextraction capillaries 143 Table 3.7 Chemical structures and pertinent physical properties of aldehydes extracted using sol-gel CN-PDMS coating 146

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ix Table 3.8 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of aldehydes extracted on a sol-ge l CN-PDMS microextraction capillary 148 Table 3.9 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of aldehydes extr acted on a sol-gel CN-PDMS microextraction capillary 149 Table 3.10 Limits of detection (LOD) data for aldehydes in CME-GC-FID using sol-gel CN-PDMS micr oextraction capillaries 150 Table 3.11 Chemical structures and pertinen t physical properties of ketones extracted using sol-gel CN-PDMS coating 151 Table 3.12 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of ketones extracted on a sol-ge l CN-PDMS microextraction capillary 153 Table 3.13 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of ketones extr acted on a sol-gel CN-PDMS microextraction capillary 154 Table 3.14 Limits of detection (LOD) data for ketones in CME-GC-FID using sol-gel CN-PDMS mi croextraction capillaries 155 Table 3.15 Chemical structures and pertinent physical properties of aromatic amines extracted us ing sol-gel CN-PDMS coating 157 Table 3.16 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of aromatic amines extracted on a sol-gel CN-PDMS microextraction capillary 159 Table 3.17 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of aromatic amines extracted on a sol-gel CN-PDMS microextraction capillary 160 Table 3.18 Limits of detection (LOD) data for aromatic amines in CMEGC-FID using sol-gel CN-PDMS microextraction capillaries 161

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x Table 3.19 Chemical structures and pertinent physical properties of chlorophenols extracted usi ng sol-gel CN-PDMS coating 163 Table 3.20 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of chlorophenols extracted on a so l-gel CN-PDMS microextraction capillary 165 Table 3.21 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of chlorophenols ex tracted on a sol-gel CN-PDMS microextraction capillary 166 Table 3.22 Limits of detection (LOD) data for chlorophenols in CME-GCFID using sol-gel CN-PDMS mi croextraction capillaries 167 Table 3.23 Chemical structures and pert inent physical properties of alcohols extracted using sol-gel CN-PDMS coating 169 Table 3.24 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of alcohols extracted on a sol-ge l CN-PDMS microextraction capillary 171 Table 3.25 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of alcohols extracted on a sol-gel CN-PDMS microextraction capillary 172 Table 3.26 Limits of detection (LOD) data for alcohols in CME-GC-FID using sol-gel CN-PDMS micr oextraction capillaries 173 Table 3.27 Chemical structures and pe rtinent physical properties of free fatty acids extracted using sol-gel CN-PDMS coating 175 Table 3.28 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area re producibility for mixtures of free fatty acids extracted on a so l-gel CN-PDMS microextraction capillary 177 Table 3.29 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary peak area reproducibility for mixtures of free fatty acids extracted on a sol-gel CN-PDMS microextraction capillary 178

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xi Table 3.30 Limits of detection (LOD) da ta for free fatty acids in CME-GCFID using sol-gel CN-PDMS mi croextraction capillaries 179 Table 4.1 Names, functions, and chem ical structures of sol-gel PEG coating solution ingredients 194 Table 4.2 GC peak area repeatability data (n=3) for alcohols obtained in CME-GC experiments conducted be fore and after rinsing the sol-gel PEG coated microextracti on capillary with a mixture (50 mL) of dichloromethane/methanol (1:1, v/v) for 24 hours 208 Table 4.3 Chemical structures and pertinent physical properties of aldehydes extracted usi ng sol-gel PEG coating 212 Table 4.4 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of aldehydes extracted on a sol-gel PEG microextraction capillary 214 Table 4.5 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of aldehydes extracted on a sol-gel PEG microextraction capillary 215 Table 4.6 Limits of detection (LOD) data for aldehydes in CME-GC-FID using sol-gel PEG microe xtraction capillaries 216 Table 4.7 Chemical structures and pert inent physical properties of ketones extracted using sol-gel PEG coating 218 Table 4.8 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of ketones extracted on a sol-ge l PEG microextraction capillary 220 Table 4.9 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of ketones extracted on a sol-gel PEG microextraction capillary 221 Table 4.10 Limits of detection (LOD) data for ketones in CME-GC-FID using sol-gel PEG microe xtraction capillaries 222 Table 4.11 Chemical structures and pertinent physical properties of aromatic amines extracted using sol-gel PEG coating 225

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xii Table 4.12 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of aromatic amines extracted on a sol-gel PEG microextraction capillary 228 Table 4.13 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of aromatic amin es extracted on a sol-gel PEG microextraction capillary 229 Table 4.14 Limits of detection (LOD) data for aromatic amines in CMEGC-FID using sol-gel PEG mi croextraction capillaries 230 Table 4.15 Chemical structures and pert inent physical properties of phenol derivatives extracted us ing sol-gel PEG coating 233 Table 4.16 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of phenol derivatives extracted on a sol-gel PEG microextraction capillary 235 Table 4.17 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of phenol derivativ es extracted on a sol-gel PEG microextraction capillary 236 Table 4.18 Limits of detection (LOD) data for phenol derivatives in CMEGC-FID using sol-gel PEG mi croextraction capillaries 237 Table 4.19 Chemical structures and pert inent physical properties of alcohols extracted using sol-gel PEG coating 239 Table 4.20 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of alcohols extracted on a sol-ge l PEG microextraction capillary 241 Table 4.21 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of alcohols ex tracted on a sol-gel PEG microextraction capillary 242 Table 4.22 Limits of detection (LOD) data for alcohols in CME-GC-FID using sol-gel PEG microe xtraction capillaries 243

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xiii Table 4.23 Chemical structures and pe rtinent physical properties of free fatty acids extracted using sol-gel PEG coating 246 Table 4.24 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak ar ea reproducibility for mixtures of free fatty acids extracted on a sol-gel PEG microextraction capillary 248 Table 4.25 Experimental data on CME-GC replicate measurements illustrating capillary-to-capillary GC peak area reproducibility for mixtures of free fatty aci ds extracted on a sol-gel PEG microextraction capillary 249 Table 4.26 Limits of detection (LOD) da ta for free fatty acids in CME-GCFID using sol-gel PEG microextraction capillaries 250

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xiv LIST OF FIGURES Figure 1.1 Custom-made SPME device based on Hamilton™ 7000 series microsyringe 5 Figure 1.2 Design of the first commercial SPME device produced by Supelco 6 Figure 1.3 Modes of extraction with coat ed fiber (a) direct extraction; (b) headspace configuration; (c) membrane protection approach 10 Figure 1.4 Schematic representation of molecular imprinting process 33 Figure 1.5 Scanning electron microsc opic images of poly(AA-VP-Bis) monolithic capillary; (a) Wide-view and (b) close-up-view 36 Figure 1.6 Design of internally cooled SPME device 41 Figure 1.7 SPME derivatization techniques 43 Figure 2.1 Overview of the sol-gel process 58 Figure 2.2 Schematics illustrating the cross sectional view of sorbentcoated SPME fiber (A), and sorb ent-coated CME capillary (B) 65 Figure 2.3 Schematic of a homemade capillary filling/purge device 67 Figure 3.1 Gravity-fed sample de livery system for capillary microextraction 109 Figure 3.2 Schematic representation of the connection of the microextraction capilla ry with the analysis column inside the GC oven using a press-fit quartz connector 117 Figure 3.3 Standard curve for 1-undeca nol obtained by direct injection into the GC under splitless mode 120

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xv Figure 3.4 Scanning electron microsc opic image of a sol-gel CN-PDMS coating on the inner surface of a fused silica capillary (250 m i.d.) used in CME illustrating uniform coating thickness on the inner surface of the fused s ilica capillary, magnification: 10,000x 129 Figure 3.5 Scanning electron microsc opic image of a sol-gel CN-PDMS coating on the inner surface of a fused silica capillary (250 m i.d.) used in CME illustrating por ous fine structure of sol-gel CN-PDMS coating, magnification: 20,000x 130 Figure 3.6 Effect of conditioning temper ature on the performance of solgel CN-PDMS microextraction ca pillary in CME of alcohols used as test solutes 132 Figure 3.7 Effect of conditioning temper ature on the performance of solgel CN-PDMS microextraction capillary in CME of PAHs used as test solutes 133 Figure 3.8 Illustration of the extraction profiles of moderately polar and polar analytes 136 Figure 3.9 CME-GC analysis of aque ous samples of PAHs on a sol-gel CN-PDMS capillary 140 Figure 3.10 CME-GC analysis of aldehydes on a sol-gel CN-PDMS capillary 147 Figure 3.11 CME-GC analysis of ketones on a sol-gel CN-PDMS capillary 152 Figure 3.12 CME-GC analysis of aromatic amines on a sol-gel CN-PDMS capillary 158 Figure 3.13 CME-GC analysis of chlor ophenols on a sol-gel CN-PDMS capillary 164 Figure 3.14 CME-GC analysis of alc ohols on a sol-gel CN-PDMS capillary 170 Figure 3.15 CME-GC analysis of free fatty acids on a sol-gel CN-PDMS capillary 176 Figure 3.16 CME-GC analysis of a mi xture of nonpolar, moderately polar and highly polar organic co mpounds on a sol-gel CN-PDMS capillary 181

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xvi Figure 3.17 CME-GC analysis of mixt ure of two alcohols and two free fatty acids on a sol-gel CN-PDMS capillary 182 Figure 3.18 CME-GC analysis of mixt ure of two alcohols and two free fatty acids on a sol-gel PDMS capillary 183 Figure 4.1 Scanning electron microscopi c image of a sol-gel PEG coating on the inner surface of a fused s ilica capillary (250 m i.d.) used in CME illustrating uniform coating thickness on the inner surface of the fused s ilica capillary, magnification: 10,000x 205 Figure 4.2 Effect of conditioning temper ature on the performance of solgel PEG microextraction capillary 207 Figure 4.3 Illustration of the extraction profiles of moderately polar and polar analytes 210 Figure 4.4 CME-GC analysis of al dehydes on a sol-gel PEG capillary 213 Figure 4.5 CME-GC analysis of ke tones on a sol-gel PEG capillary 219 Figure 4.6-A CME-GC analysis of aromatic amines on a sol-gel PEG capillary 226 Figure 4.6-B CME-GC analysis of aromatic amines on a sol-gel PEG capillary 227 Figure 4.7 CME-GC analysis of phe nols on a sol-gel PEG capillary 234 Figure 4.8 CME-GC analysis of al cohols on a sol-gel PEG capillary 240 Figure 4.9 CME-GC analysis of fr ee fatty acids on a sol-gel PEG capillary 247 Figure 4.10 CME-GC analysis of a mixtur e of moderately polar and highly polar organic compounds on a sol-gel PEG capillary 252 Figure 4.11 CME-GC analysis of mixt ure of two alcohols and two free fatty acids on a sol-gel microe xtraction capillary prepared using TESP 253

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xvii Figure 4.12 CME–GC analysis of mixt ure of two alcohols and two free fatty acids on a sol-gel microe xtraction capillary prepared without TESP 254

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xviii LIST OF SCHEMES Scheme 2.1 Key reactions in sol-gel prosess 57 Scheme 2.2-A Mechanism of acid catalyzed sol-gel reactions 61 Scheme 2.2-B Mechanism of base catalyzed sol-gel reactions 62 Scheme 3.1 Hydrolysis of 3-cyanopr opyltriethoxysilane (precursor) and tetraethoxysilane (co-precursor) 123 Scheme 3.2-A Growth of sol-gel CN-PDMS polymer chains within a fused silica capillary via po lycondensation of a hydrolyzed precursor (A) and a hydrolyzed co-precursor (B) 124 Scheme 3.2-B Growth of sol-gel CN-PDMS polymer chains within a fused silica capillary via polycondensation of precursors (C) and a sol-gel active polymer (D) 125 Scheme 3.3 Sol-gel CN-PDMS coating chemically anchored to the inner walls of fused silica capillary 126 Scheme 3.4 Deactivation of sol-gel CN-PDMS coating chemically anchored to the inner walls of fused silica capillary 127 Scheme 4.1 Hydrolysis of methy ltrimethoxysilane (precursor) and N(triethoxysilylpropyl)-O-polyethyl ene oxide urethane (sol-gel co-precursor with bonded PEG moiety) 202 Scheme 4.2 Growth of sol-gel PEG polymer chains within a fused silica capillary via polycondensation of a hydrolyzed sol-gel precursor (A) and a hydrolyzed sol-gel co-precursor (B) 203 Scheme 4.3 Sol-gel PEG coating chemically an chored to the inner walls of fused silica capillary 204

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xix LIST OF SYMBOLS AND ABBREVIATIONS a Activity of analytes AA-VP-Bis Acrylamide-VinylPyridineN, N’ -methylene bisacrylamide AN Nucleophilic Addition ACF Active Carbon Fiber ACN Acetonitrile ADS Alkyl-Diol-Silica AFM Atomic Force Microscopy Amide bridged calix[4]arene 25,27-dihydroxy-26,28-oxy (2 ,7 -dioxo-3 ,6 -diazaoctyl)oxy-ptert-butylcalix[4]arene AMTEOS Anilinemethyltriethoxysilane APs Alkyl Phenols ASE Accelerated Solvent Extraction B15C5 3 -allylbenzo-15-crow-5 ether bp Boiling Point BMA Butyl Methacrylate BPA Bisphenol-A BTEX Benzene, Toluene, Ethylbenzene, and Xylene C8 Octyl C18-TMS N-octadecyldimethyl[3-(tri methoxysilyl)propyl] ammonium chloride CAR Carboxen CE Capillary Electrophoresis CEC Capillary Electrochromatography CEES 2-chloroethyl ethyl sulfide CME Capillary Microextraction CN-PDMS Cyanopropyl-Poly(dimethylsiloxane) CP Chlorophenol CW Carbowax d Density DATEG -Diallyltriethylene Glycol DB18C6 4-allyldibenzo18-crown-6 ether DBUD14C4 Dibutyl-unsymmetric-dibenzo-14crown-4-dihydroxy crown ether DCCA Drying Control Chemical Additive DEHP Di-(2-ethylhexyl)phosphoric acid DI Deionized

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xx DiglycidyloxyC[4]arene (5,11,17,23-tetra-tert-but yl)-25,27-dihydroxy-26,28diglycidyloxycalix[4]arene DHSU14C4 Dihydroxy-substituted saturated urushiol crown ether DOH-B15C5 Dihydroxy-terminated benzo-15-crown-5 DM-CD Heptakis (2,6-diO -nethyl)-cyclodextrin DVB (or DB) Divinylbenzene ECD Electron Capture Detection EGDMA Ethylene Glycol Dimethacrylate EOF Electroosmotic Flow EP Ephedrine EPA Environmental Protection Agency EXAFS X-Ray Absorption Fine Structure Spectroscopy FID Flame Ionization Detector FTIR Fourier Transform Infrared Spectroscopy GAA Glacial Acetic Acid GC Gas Chromatography GBC Graphitized Carbon Black HMDS 1,1,1,3,3,3-Hexamethyldisilazane HPLC High-Performance Liquid Chromatography HS-SPME Headspace Solid-Phase Microextraction i.d. Inner Diameter INCAT Inside Needle Capillary Absorption Trap LC-MS Liquid Chromatography-Mass Spectrometry K Distribution constant KH-560 3-(2cyclooxypropoxyl)propyltrimethoxysilane LLE Liquid-Liquid Extraction LOD Limit of Detection MA Methyl Acrylate MAA Methacrylic Acid MAE Microwave-Assisted Extraction MAHs Monocyclic Aromatic Hydrocarbons MeOH Methanol MIP Molecularly Imprinted Polymer MMA Methyl Methacrylate MP Methamphetamine MS mass spectrometry MTMOS Methyltrimethoxysilane MW Molecular Weight nD Refractive Index NMR Nuclear Magnetic Resonance

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xxi OCPs Organochlorine Pesticides ODS Octadecylsilane OH-DB14C4 Hydroxy-Terminated Dibenzo-14-Crown-4 OH-TSO Hydroxy-terminated Silicon Oil OPPs Oganophosporuos Pesticides OTCs Open-Tubular Capillary Columns OTEC Open-Tubular Electrochromatography OTLC Open-Tubular Liquid Chromatography PA Polyacrylate PAEs Phthalic acid esters PANI Polyaniline PAHs Polycyclic Aromatic Hydrocarbons PCBs Polychlorinated Biphenyls PDMDPS Poly(dimethyldiphenylsiloxane) PDMS Poly(dimethylsiloxane) PEEK Polyetheretherketone PEG Polyethylene Glycol PF Polysilicone Fullerene PheDMS Phenyldimethylsilane PLAC Porous Layer Activated Charcoal PLE Pressurized Liquid Extraction PMHS poly(methylhydrosiloxane) PMPVS Polymethylphenylvinylsiloxane PPY Polypyrrole PPPY Poly-N-Phenylpyrrole PTMO Polytetramethylene oxide PVA Poly(vinyl alcohol) RAM Restricted Access Material RPLC Reversed-Phase Liquid Chromatography RPM Revolution per Minute RSD Relative Standard Deviation S/N Signal to Noise SN Nucleophilic Substitution SAM Self-Assembled Monolayer SEM Scanning Electron Microscopy SFC Supercritical Fluid Chromatography SFE Supercritical Fluid Extraction SPE Solid-Phase Extraction SPME Solid-Phase Microextraction Tg Glass transition termperature

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xxii TEOS Tetraethylorthosilicate (or Tetraethoxysilane) TESP N-(Triethoxysilylpropyl)-O-Pol yethylene Oxide Urethane TFA Trifluoroacetic Acid THF Tetrahydrofuran TEOS Tetraethylorthosilicate (or Tetraethoxysilane) TMSPMA 3-(trimethoxysilyl)propyl methacrylate TR Templated Resin UV Ultraviolet VOC Volatile Organic Compound VTEOS Vinyltriethoxysilane XANES X-Ray Absorption Near Edge Spectroscopy XPS X-Ray Photoelectron Spectroscopy

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xxiii Sol-Gel Immobilized Cyano-Polydimethylsilo xane and Short Chain Polyethylene Glycol Coatings for Capillary Microextraction Coupled to Gas Chromatography Sameer M. Kulkarni ABSTRACT Two highly polar sol-gel coat ings were developed for capillary microextraction (CME). One of the coatings contained cy anopropyl-polydimethyl siloxane (CN-PDMS) and the other low molecular weight polyeth ylene glycol. These highly polar coatings were immobilized via sol-gel chemistry allowing for direct chemical bonding to the inner surface of fused silica capillaries. These solgel coated microextract ion capillaries were employed in CME for solvent-free microextrac tion and preconcentration of trace analytes (polar, moderately polar, and nonpolar) from aqueous matrices. CN-PDMS and short chain PEG extraction phases e xhibit both polar and polarizable characteristics. Therefore, both sol-gel CN-PDMS and short chain sol-ge l PEG coatings were able to extract analytes of different polarity from aqueous media. Both sol-gel CN-PDMS and sol-gel PEG coatings provided effective extraction of polar analytes such as free fatty acids, alcohols, and phenols without re quiring derivatization, pH adjustment or salting out procedures commonly used in SPME experime nts with conventional coatings. For each of these coatings, detection limits on the orde r of nanogram/liter (ng/ L) were achieved for both polar and nonpolar analytes extracted si multaneously from aqueous media followed

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xxiv by GC-FID analysis. Both sol-gel CN-PDM S and short chain sol-gel PEG coated microextraction capillaries showed excel lent run-to-run and capillary-to-capillary extraction reproducibility (GC peak area RSD < 6% & 5%, respectively) for nonpolar as well as polar analytes. For the sol-gel CN-PDMS coatings, the upper allowable conditioning temperatures were 330 C a nd 350 C, for the extr action of polar and nonpolar organic analytes, respectively. Similarl y, the sol-gel PEG coatings used for the extraction of polar organic analytes surviv ed a conditioning temperature of 340 C. Both sol-gel CN-PDMS and sol-gel PEG coated microextraction capillaries showed no significant changes in the peak areas of the extracted analytes even after being washed with organic solvents (dichloromethane a nd methanol (1:1), v/v) for 24 hours. The excellent thermal and solvent stabilities can be attributed to the presence of chemical bonds between the sol-gel coatings and the fused silica surface.

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1 CHAPTER 1 AN INTRODUCTION TO SOLI D-PHASE MICROEXTRACTION 1.1 An overview on sample preparation During the past several decades, public awareness of health risk associated with environmental contaminants has stimulated interest in environmental research and monitoring which, in turn, has resulted in a requirement for the determination of toxic contaminants in air, water, and solids, including soil and sediment samples. The conventional approaches to sample preparatio n and analysis are not usually in keeping with the determination of complex environmental samples. In general, an analytical method invol ves several processes such as sampling (collection of a representative sample), sa mple preparation (isolation from the matrix, preconcentration, fractionation and, if necessa ry, derivatization), separation, detection, and interpretation of the analytical data. Th ese analytical steps are followed consecutively, and therefore, overall speed of any analysis is determined by the speed of the slowest step. Since the success of an analytical proce dure depends on the performance of each individual step, it is imperative to monito r each step. Typically, conventional sampling and sample preparation methods are timeconsuming and labor-intensive processes involving multi-step procedures that often employ significan t amounts of harmful organic solvents and are often prone to analyte loss es. Surveys show that more than 80% of

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2 analysis time is spent on sample collection a nd sample preparation [1]. This is necessary because in most cases analytical instrument s cannot handle the sample matrices directly. The whole analytical process ca n be wasted if an unsuitable sample preparation method is employed before the sample reaches the analytical instrument [2,3]. Classical sample preparation methods incl ude various extraction techniques, such as Soxhlet extraction [4], liquid-liquid ex traction (LLE) [5], accelerated solvent extraction (ASE) [6], microwave-assisted solvent extraction (MAE) [7], solid-phase extraction (SPE) [8], supercri tical fluid extraction (SFE) [9 ], and purge-and-trap [10]. Sample preparation procedures using solven ts consume large amounts of solvents, thus creating environmental and occupational haza rds. Moreover, they are time-consuming, labor-intensive and involve multi-stage operatio ns. Each step can introduce errors and analyte losses, especially when preparing samp les containing volatile analytes. The use of SPE cartridges [11,12] has redu ced many limitations of clas sical extraction methods. SPE needs less solvent but it is a time-consumi ng multi-step process and often requires an analyte preconcentration step via solvent evap oration, which may result in the loss of volatile components. Adsorption of analytes on the walls of extraction devices may occur, and trace impurities in the extraction solvent may simultaneously become concentrated. Even though the volume of organic solvents ne eded for SPE is much less than that for LLE or Soxhlet extraction techniqu es, it is still significant. In order to eliminate limitations inherent in classical sampling and sample preparation methods, Belardi and Pawliszyn [ 13] introduced solid-phase microextraction (SPME) in 1989. SPME integrates sampling, ex traction, preconcentration and sample

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3 introduction into a solvent-free single-step procedure. SPME saves sample preparation time and solvent disposal costs and provides im proved detection limits for target analytes both in the laboratory and in the field. 1.2 History of SPME In late 1980s, when Paw liszyn and co-workers [14] were involved in laser desorption/fast gas chromatography experiments, the sample preparation step took hours. In such an experiment, one e nd of an optical fiber was dipp ed in the solvent extract of target analytes and the volatile solvent wa s removed through evaporation, thus coating the fiber with the sample. The coated end of the fiber was then inserted into the GC injection port and analytes were desorbed onto the GC column using a laser pulse. Although, use of laser pulse and high speed GC instrument was time efficient, the much slower sample preparation tec hnique prolonged the overall anal ysis time. To address this problem, optical fibers with polymeric coati ngs were used. The orig inal purpose of these coatings was to protect the optical fibers from breakage. Since the coatings were thin (10100 m), the expected extraction times for these systems were short. The preliminary work on SPME involve d uncoated and coated (with liquid and solid polymeric phases) fused silica optical fibers. The extraction was performed using sections of these fibers dipped into the a queous sample containing tests analytes. These analytes were then desorbed by placing th e fibers in GC injection port. The early experimental data indicated the effectivene ss of this novel but simple approach to the

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4 extraction of both nonpolar and polar analytes from aqueous samples in a reproducible manner. Promising results from these preliminary experiments accelerated the development of first SPME device which inco rporated a coated fuse d silica fiber into a Hamilton™ 7000 series microsyringe [15]. As shown in figure 1.1, the plunger of the microsyringe was replaced with stainless steel microtubing. The out er protective coating (5 mm) was removed before inserting 1.5 cm l ong fused silica fiber into the microtubing. Using epoxy glue the fiber was mounted on the plunger cap. Movement of the plunger allowed exposure of the fiber (coated or uncoated with polymeric phase) during extraction and desorption of targ et analytes. The syringe need le protected the fiber during storage and penetration of the septum of GC injection port. Later, after few modifications, an improved version of SPME device was intr oduced [15]. Figure 1.2 illustrates the first commercial SPME device. In this configurat ion, the outer surface of a small piece of fused-silica fiber (~ 1 cm at one end) is co ated with a polymeric sorbent. The fiber is mounted on the SPME syringe by securing the unco ated end of the fibe r with the plunger. The thickness of the SPME coating gene rally ranges between 10 m and 100 m. Thermally stable polar or nonpolar polymeric sorbents that allow fast solute diffusion are suitable for use as the extracting phase. Polymers that have been used include poly(dimethylsiloxane) (PDMS) poly(divinylbenzene) (PDB), poly(acrylate) (PA), Carboxen (CAR), a carbon molecular sieve, an d Carbowax (CW; polyethylene glycol). For a particular extraction pr oblem, the extracting phase is selected based on analyte affinity.

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5 Figure 1.1 Custom-made SPME device based on Hamilton™ 7000 series microsyringe. Reproduced from ref. [15] with permission.

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6 Figure 1.2 Design of the first commercia l SPME device produced by Supelco. Reproduced from ref. [15] with permission.

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7 The SPME device facilitates two major operations: (a) extraction of target analytes, and (b) transfer of the extracted analytes from the fiber to the analytical instrument. The polymeric sorbent coati ng provides a single step extraction and preconcentration of analytes by reaching extr action equilibrium with the sample matrix. The extracted analytes are then desorbed into an analytical instrument for separation and analysis. The thermal desorption process is t ypically carried out by placing the fiber in a GC injection port. The sorbent coating on the outer surface of fused silica fiber, however, is not well-suited for hyphenation with liqui d phase separation techniques (e.g., HPLC, CE, CEC, etc.) because organic solvents used to desorb the extracted analyte(s) may also strip the coating off the fiber, since on a c onventionally coated SPME fiber the coating is held on the surface merely by the physical force of adhesion (i.e., no chemical bond between the coating and the fi ber surface). The incompatibility of fiber-based SPME with liquid phase separation techniques led to the de velopment of so called in-tube SPME [16]. In this format, the target analytes are extrac ted by the sorbent coated on the inner surface of a capillary and after reaching the extracti on equilibrium, the extracted analytes are desorbed into a liquid-phase separation co lumn (e.g., HPLC) using the organo-aqueous mobile phase or organic solvent. One important requirement for the implementation of SPME with a liquid-phase separation technique is the stability of the SPME coating under operational conditions involving orga no-aqueous desorbing solvents. Most conventionally prepared GC coatings that ar e used for this purpose do not satisfactorily fulfill this requirement, since they are not bonded to the capillary surface.

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8 1.3 Extraction modes in SPME As mentioned earlier, in SPME, the extr acting phase can be ei ther on the outer surface of a fiber (fiber-SPME) or on the inne r surface of a capillary (in-tube SPME, also known as capillary microextrac tion (CME)) [17]. SPME can be used for solid, liquid, and gaseous samples. 1.3.1 Modes of extraction with coated SPME fiber There are three different extraction (SPME) modes that can be performed using coated fibers: (I) direct extraction, (II) headspace extraction, and (III) a membrane-protected extraction. In direct extraction mode (Figure 1.3 (a)), th e coated fiber is immersed into the sample and the analyte(s) are transported directly from the sample matrix to the extracting phase. Usually agitation is employed to facilitate the transport of analyte(s) from the bulk of the solution to the vicinity of extracting phase. Fo r gaseous samples, natural convection of air is sufficient to facilitate equilibrium extrac tion. In case of aqueous samples, a variety of agitation methods, such as fast sample flow, rapid vial or fiber shaking, stirring or sonication of the aqueous sample may be em ployed. In direct SPME, extracting phase is kept in contact with sample matrix containi ng target analyte(s) fo r predetermined amount of time. When concentration equilibrium is reached between the sample matrix and the extracting phase, exposing the extracting phase to the sample for longe r time will not lead to any further accumulation of the analyte(s). The equilibrium conditions can be

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9 described by the following equation [18]: nf = Kfs Vs Vf CoKfsVf + Vs( 1.1) Where, nf: number of moles of the analyte(s) accumulated on the extracting phase, Vf: volume of the extracting phase, Vs: volume of the sample, Co: initial analyte concentration in the sample, Kfs: distribution constant of the analyte between extracting phase and sample matrix. The equation 1.1 is limited to partitioning equilibrium involving liquid polymeric extracting phases and indicates that after e quilibrium has been reached, the amount of analyte extracted on the coating is dire ctly proportional to the initial analyte concentration in the sample. This is the ba sis for analyte quantification by SPME. When the sample volume is very large compared to the volume of extracting phase, the value of the term Kfs Vf becomes insignificant. Hence, equation 1.1 can be simplified as: nf=Kfs V fCo ( 1.2) It is clear from equation 1.2 that the amount of extracted analyte(s) is independent of the sample volume making SPME a very effectiv e technique for field applications. It eliminates the need for colle cting the known amount of sample prior to analysis because extracting phase can be directly exposed to the air, water, stream etc. Thus, SPME

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10 Figure 1.3 Modes of extraction with coated fibe r (a) direct SPME; (b) headspace SPME; (c) membrane-protected SPME. Adapted from ref. [19] with permission. Coating Sample Sample Coating SPME fiber Protective membrane HeadspaceHeadspace (a) (b) (c)

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11 combines sampling and sample preparation in a single step eradicating the errors associated with analyte(s) losses through decomposition or adsorption on the walls of sampling container. In headspace SPME (HS-SPME) (Figure 1.3 (b)), the aqueous sample containing target analyte(s) is placed in a sealed c ontainer and with the help of the SPME syringe, the fiber is introduced into the headspace (gaseous space above the liquid sample) of the container without immersing the coated fibe r into the sample matrix. The main purpose of this modification is to avoid the damage to the fiber coating from undesirable sample matrix interferences (e.g., high molecular mass compounds, humic ma terials, proteins, etc.). In addition, such an extraction mode allows alterations to the sample matrix (e.g., change in pH, addition of salts, etc.) that are frequently used to ameliorate the extraction efficiency. The equilibrium analyte distributions taking place in HS-SPME are: (1) between the aqueous phase (sample matrix) a nd gaseous phase (in th e headspace) of the closed container (Eq. 1.3), and (2) between th e gaseous phase and extracting phase (fiber coating) (Eq. 1.4). Khs = ChCs(1.3) and, Kfh = CfCh(1.4) Where, Khs: the distribution constant between the headspace and the aqueous phase; Ch : the concentration of the analyte(s) in the gaseous phase (or headspace) at

PAGE 39

12 equilibrium; Cs : the concentration of the analyte in the aqueous phase at equilibrium; Kfh: the analyte distribution constant between the extracting phase and the headspace; Cf : analyte concentration in the extracting phase at equilibrium. The mass of an analyte extracted by coating on the fiber is related to overall equilibrium of the analyte in the three-phase system. Sin ce the total mass of an analyte should remain constant during the extraction: CfVf+ C0Vs = ChVh+ CsVs (1.5) where, C0: the initial concentration of th e analyte in the sample matrix; Vf: the volume of the extracting phase on the SPME fiber; Vh: the volume of the gaseou s phase (or headspace); Vs: the volume of the sample matrix. The number of moles of the analyte extracted by the extracting phase, nf = Cf Vf can be expressed as [18]: nf = Kfh Khs Vf C0 VsKfh Khs Vf + Khs Vh + Vs(1.6) Also, Kfs = KfhKhs = KfgKgs, since the extracting phase/headspace distribution constant,

PAGE 40

13 Kfh, can be approximated by the stationary phase/gas distribution constant, Kfg, and the headspace/sample dist ribution constant, Khs, can be approximated by the gas/sample distribution constant, Kgs. If the moisture effect in th e gaseous headspace is neglected, equation 1.6 can be rewritten as: nf = Kfs Vf C0 VsKfs Vf + Khs Vh + Vs(1.7) Equation 1.7 shows that the amount of extracted analyte is independent of the location of the fiber in the system. It may be placed in the gaseous phase or directly in the aqueous phase as long as all other pa rameters, such as the volume of the stationary phase, headspace, and the sample matrix, remain constant. In case of protected-membrane extraction (Figure 1.3 (c)), the preliminary goal is to protect the fiber coating against the da mage from unwanted interferences that maybe present in the sample matrix. This approach is mainly advantageous for selective extraction of target analyte(s) by choosi ng the membrane of desired properties. The slower kinetics of membrane extraction is the major disadvantage since the analyte(s) must diffuse through the membrane before th ey can reach the coating. The use of thin membranes and elevated extraction temperat ures may accelerate the extraction process [20].

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14 1.3.2 Modes of extraction with in-tube SPME There are two different modes of extr action with in-tube SPME: active or dynamic where sample matrix containing the ta rget analyte(s) is passed through the tube coated with extracting phase (coating), and pa ssive or static where the sample matrix containing target analyte(s) is kept in the tube coated with extracting phase (coating) allowing the analyte(s) to diffuse into the coating. In dynamic in-tube SPME, a piece of fused silica capillary typically coated with thin film of the extracting phase or a capillar y packed with extracting phase dispersed on an inert support material (a piece of micro-LC capillary column) is used for extraction of target analyte(s). The anal yte front migrates through th e capillary with a speed proportional to the linear velocity of the sa mple matrix, and inversely related to the partition ratio. For the in-tube SPME using shor t capillaries, the mini mum extraction time at equilibrium can be expressed as [19]: Kes V eVv (1.8)1 + te = u L where, te: extraction time required to reach concentr ation equilibrium between analyte(s) and extracting phase; L: length of the extraction capillary; Kes: analyte distribution constant betw een extracting phase and sample matrix;

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15 Ve: volume of the extracting phase; Vv: void volume of the tubing c ontaining the extracting phase; u: chromatographic linear velocity. In static in-tube SPME, similar to dyna mic in-tube SPME, a piece of fused silica capillary coated with a thin film of the ex tracting phase or packed with extracting phase dispersed on an inert su pport material is used for extraction of target analyte(s). However, the sample matrix containing target analyte(s) is kept (static) inside the coated or packed capillary. In this case, the only mechanism of analyte transport (and preconcentration) is diffusion through sample matrix contained in the capillary. The static in-tube SPME is particularly suitable for field sampling. 1.4 Coatings used in fiber SPME and in-tube SPME 1.4.1 Coatings used in fiber SPME Several different methods can be employe d to prepare SPME fibers coated with an extraction phase (coating). In the dipping te chnique, fiber is placed in a concentrated organic solvent solution of the (polymeric) extracting phase for a brief period of time. Subsequently, the fiber is removed from th e solution and the solvent is evaporated creating a coating on the fiber [13]. The same method can be expanded to electrodeposition of sel ective coatings on the surface of metallic rods [21]. The

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16 preparation of commercial ex tracting coating is carried out simultaneously during the drawing of the fused silica rod to maintain the reproducibility of th e coating thickness. Coatings used in fiber SPME can be compile d into two major groups: (a) commercially available coatings and (b) tailor-made coatings. 1.4.1.1 Commercially available co atings for fiber SPME Currently a number of coatings with different thicknesses are commercially available: poly(dimethylsiloxane) (PDMS), pol yacrylate (PA), also the composite (mixed phase) coatings such as Polydimethyls iloxane/Polydivinylbenzene (PDMS/PDVB), Carboxen/Polydimethylsiloxane (CAR /PDMS), Carbowax/Polydivinylbenzene (CW/PDVB), Carbowax/Templated Resin (CW/TR), Polydiviny lbenzene-CarboxenPolydimethylsiloxane (PDVB/CAR/PDM S). Table 1.1 shows the summary of commercially available polymers used as fiber SPME coatings. Poly(dimethylsiloxane) (PDMS) and pol yacrylate (PA) are the homogeneous polymeric sorbents used in SPM E. PDMS [22] has been the mo st frequently used sorbent in SPME because of its inherent versatil ity, high thermal stability, and extraction efficiencies for wide range of analytes. Commercially availa ble PDMS coated fibers have PDMS sorbent immobilized on the fiber using a cross-linkable functionality present in the polymeric structure. This cross-linking pr ovides PDMS coatings with higher thermal stability (~ 340 C) as well as solvent stabi lity [23]. However, due to the difficulty of stabilizing thick coatings through cross-li nking reaction, the only commercially available

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17 Table 1.1 Commercially available fiber coati ngs for SPME and their applications. Adapted from refs. [44-46] with permission. Fiber Coating Coating Thickness (m) Max. Temp. (for GC use) (C) Application Poly(dimethylsiloxane) (PDMS) 100c 30c 7a 280 280 340 GC/HPLC, Nonpolar organic compounds such as VOCs, PAHs and BTEX Polyacrylate (PA) 85b 320 GC/HPLC, Polar organic compounds such as triazines and phenols PDMSpolydivinylbenzene (PDMS-PDVB) 65b 60b,d 270 GC/HPLC, PAHs, aromatic amines, VOCs Carboxen-PDMS (CAR-PDMS) 85b 75b 320 320 GC/HPLC, VOCs and hydrocarbons Carbowaxpolydivinylbenzene (CW-PDVB) 70b 65b 265 265 GC/HPLC, Polar analytes such as alcohols and polar compounds Carbowax-templated resin (CW-TR) 50b HPLC, Anionic surfactants and aromatic amines PolydivinylbenzeneCarboxen-PDMS (PDVB-CAR-PDMS) 50/30b 270 GC/HPLC, Odors and flavors aCross-linked phase; bPartially cross-linked phase; cNon cross-linked phase; dGC

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18 PDMS coated fiber that can withstand solv ent rinsing is the one with 7 m coating thickness. PDMS is a nonpolar polymer which usually extracts nonpolar analytes such as volatile organic compounds (VOCs) [24,25], PAHs [26,27], alkanes [28,29] BTEX compounds (benzene, toluene, ethylbenzene, and xylene) [22,30], a nd some pesticides [31,32] Polyacrylate (PA) [33] is a highly polar sorbent immobilized by partial crosslinking. It is commercially available in 85 m thickness. Due to its high polarity, PA coating is frequently used for extraction of polar analytes such as alcohols [34,35], organic acids [36,37], aromatic amines [ 38,39], phenols and their derivatives [33,40,41] and polar pesticides [40,42] from various matr ices. Polyacrylate is a rigid, low density solid polymer at room temperature. Consequently, the extraction times tend to be longer because of slower analyte diffusion. [41,43]. The composite (mixed phase) coatings were introduced to enhance the selectivity toward target analytes. They are prepared by embedding porous particles (one or more types) in the partially cross-linked polyme ric phase. However, compared to homogeneous polymeric coatings (PDMS and PA) composite coatings have lower mechanical stability. Introduced in 1996, Polydimethylsiloxane/Pol ydivinylbenzene (PDMS/PDVB) [47], is suitable for extraction of polar compounds like alcohols, amin es, etc. [48]. Carboxen/Polydimethylsiloxane (CAR/PDMS) [49] and Carbowax/Polydivinylbenzene (CW/PDVB) [50] coated fibers were in troduced in 1997. CAR/ PDMS coating has a highly porous polymeric material named Car boxen and used in SPME for the extraction of VOCs [51] and hydrocarbons [52]. CW/PDVB is a blend of porous PDVB and polar

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19 Carbowax polymeric phase. Similar to PDMS /PDVB, CW/PDVB coating is also used for extraction of polar compounds (e.g., alcohols) [53]. But the swelling tendencies of Carbowax in water and its oxygen se nsitivity at temperatures above 220 C are the major drawbacks of CW/PDVB. Like other compos ite coatings, Carbowax/Templated Resin (CW/TR), is made by blending porous temp lated resin with polar Carbowax polymer. Due to the presence of both hydrophilic (C arbowax) and hydrophobic (Templated Resin) moieties in this polymeric blend, it provides re markable selectivity for the extraction of surfactants from aqueous media [54]. Polydivinylbenzene-CarboxenPolydimethylsiloxane (PDVB/CAR/PDMS), a blend of highly porous PDVB and CAR polymeric material with liquid PDMS, was introduced by SUPELCO in 1999 [55] This composite phase is used to extract analytes (C3-C20) from wide range of polarity [56,57]. 1.4.1.2 Tailor-made coatin gs for fiber SPME In general, tailor-made sorbents coat ed on SPME fiber can be grouped into different classes: carbonaceous sorbents, bonde d-phase silica sorbents, coated metallic SPME fibers, and miscellaneous sorbents. 1.4.1.2.1 Carbonaceous sorbents Carbonaceous sorbents are homogeneous, highly porous, and thermally stable. Due to these characteristics, they are favor able for SPME. Mangani and co-worker [58] reported a fused silica fiber coated with grap hitized carbon black (GCB) for extraction of

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20 VOCs from various matrices. A porous layer of activated charcoal (PLAC) coated SPME fibers used for the extraction of BTEX a nd PAHs showed significantly high thermal stabilities (> 320 C) [59,60]. SPME coating developed by Farajzadeh and co-worker [61] by mixing activated charcoal with PVC powder (ratio of 90:10) was very efficient in extracting low molecular weight alkanes. Later experiments involving a coating made with activated charcoal and PVC (ratio 70:3 0) demonstrated successful extraction of organophosphorous pesticides from an aqueous matrix [62]. Jia and co-workers [63] reported the use of active carbon fiber (ACF) as SPME sorbent. It showed efficient removal of sulfur dioxide and nitric oxide in flue gas from coal combustion. Olesik and Co-workers have used glassy carbon as a SPME sorbent for extraction of taste and odor contaminants (geosmin, 2-methylisoborne ol, and 2,4,6-trichloroa nisole commonly found in water supplies) [64], volatile organi c compounds (2-methylheptane, styrene, propylbenzene, decane, undecane) [65], a nd halogenated compounds (fluorobenzene, chlorobenzene, bromobenzene, and iodobe nzene) [66] from aqueous samples. 1.4.1.2.2 Bonded-phase silica sorbents In SPME, it is desirable to employ th ick coatings to achie ve higher extraction sensitivity. However, the use of thicker coat ings leads to longer extraction times due to slow diffusion on analytes into the extrac ting phase. Lee and co-workers [67] used bonded phase silica particles to achieve s horter extraction tome and high extraction efficiency in SPME based on thinner coatings. Comparison of a 30 m coating of bonded

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21 phase silica particles (C8-, C18-) and a conventional SPME coating (100 m PDMS) showed that the surface area of a coating ma de with the bonded phase silica particles was 500 times greater than that of conventio nal SPME coating. Therefore, extraction sensitivity of bonded phase silica coating was significantly higher compared to a conventional PDMS coating. For example, C8 -bonded phase silica coated fiber extracted ~ 40 ng of toluene from a 0.1 mg/L aqueous sample of toluene whereas PDMS coated fiber extracted only ~ 5 ng of toluene under same conditions. Among all the bonded phases investigated (C8-, C18-, phenyl), C18-bonded phase silica coatings showed highest sensitivity toward PAHs [68]. A mesoporous silica material (C16-MCM-41) characterized by its large su rface area (1028 m2 g -1) was us ed as an SPME sorbent by Hou and co-workers [69]. The me soporous silica coating (100 m) was immobilized onto a stainless steel wire by epoxy glue and show ed very high extraction efficiency for the extraction of PAHs. 1.4.1.2.3 Coated metallic SPME fibers Currently, almost all the conventional SPME fibers are made of fused silica. With no protective polyimide coating on the coated segment, the fused silica SPME fiber is very fragile and requires great care during handl ing of the SPME device. Therefore, some researchers have explored the use of miniaturized metallic rods as an alternative to fragile silica-based SPME fibers [70-74]. These metal rod themselves or an oxide layer formed on the metal surface have served as the SPME sorbent. Guo and co-workers used carbon

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22 steel electrode (140 m) coated with electrochemically deposited 10 m thick gold coating for extraction of inorganic mercury i ons in aqueous matrix [72]. Djozan and coworkers [70] evaluated different types of al uminum-based wires: (a) polished aluminum wire, (b) aluminum wire coated with oxidation product (Al2O3), and (c) anodized aluminum wire as the extraction sorbents for SPME. In their experiments, anodized aluminum wire was found to be 30 times mo re sensitive than oxidized aluminum wire. The increased sensitivity of the anodized co ating was explained by adsorptive nature of the thick Al2O3 bed formed on the aluminum wire surface during anodizing process and the inherent porous structure of the coated aluminum oxide bed. Anodized aluminum wire was used to extract aliphatic alcohols, BTEX, and petroleum products from gaseous samples. High thermal stability (~300 C), mechanical strength, low cost, and long life span are among the important advantages of an odized aluminum wires. Later, the same researchers developed copper wi res coated with a thin laye r of microcrystalline copper chloride (CuCl) [74] and copper sulfide co ating [73] as new SPME fibers (with high selectivity, sensitivity, and durability) for the extraction of low molecular weight aliphatic amines. Low molecular weight alipha tic amines are importa nt air pollutants and most of them are toxic, sensitizers and i rritants to the skin, mucous membrane, and respiratory tract [74]. Due to their high polarity, extraction and preconcentration of aliphatic amines from aqueous media is very difficult and derivatization techniques are often needed to extract these aliphatic amin es. Copper wire coated with microcrystalline copper chloride (CuCl) developed by Djozan and co-wor kers showed high selectivity toward aliphatic amines [74]. The selectivity of CuCl was explained by its reactive nature

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23 and ability to form coordinate bond with lig and such as amine group to form amino complex (Cu(amine)xCl). At high temperatures (during desorption in the GC injection port), the copper amino complex breaks apart to release free amine. Similarly, copper sulfide coated copper wire was found to be very efficient and selective in extracting aliphatic amines and alcoho ls [73] directly from aq ueous samples without any derivatization process. 1.4.1.2.4 Miscellaneous sorbents In addition to the aforementioned sorben ts, miscellaneous sorbents have been explored for SPME of various analytes. Li and co-workers [75] us ed plasticized poly(vinylchloride) as an SPME sorbent coated on a primed steel rod. The device was us ed to extract barbiturates from urine and bovine serum samples for further analysis by CE. They reported ex traction in the 0.1-0.3 mg/L and ~ 1 mg/L concentration range fo r urine and serum samples, respectively. For the extraction of polar compounds (alcohols) from liquid matrices, Gorecki and co-workers [76] used Nafion perfluor inated resin as a sorbent for fiber SPME. Amongst the polar compounds tested, Nafion showed very high affinity toward methanol – an analytical task that is difficult to accomplish using conventional SPME coatings. Xiao and co-workers [77] developed a pol ysilicone fullerene (PF) coating (33 m) as SPME sorbent for extraction of BTEX and PAHs. Due to its high thermal stability (~

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24 360 C), and good selectivity towards aromat ic compounds, fullerene has long been known as a chromatographic material [78-82] They compared the efficiency of two coatings, one made of pure PF and the other made of a mixture of PDMS and PF (4:1 ratio). Coating obtained from pure PF showed better sensitivity toward the test analytes than the mixed one. Harvey and co-workers [83] develope d a novel SPME coating consisting of hydrogen bond acidic hexafluorobispheno l groups alternat ing with oligo (dimethylsiloxane) segments to detect trace le vels of chemical warfare agents. The new coating demonstrated remarkable affinity ( 22-fold higher affinity than commercial PDMS coated fiber) towards sarin, a nurve gas. Another important contribution was the in troduction of polypyrro le (PPY) and its derivative poly-N-phenylpyrrole (PPPY) SPM E-coatings by Pawliszyn and co-workers [84]. These sorbents have drawn much attent ion due to their ability to form stable polymeric films by electrochemical and chemical means on metal and fused silica substrate, respectively. Wu and co-workers [85] have given a detail account on the preparation of PPY and PPPY coatings on meta l fibers (e.g., Pt, Au, stainless steel) as well as on the fused silica surface. They also demonstrated a wide range of applications of the PPY coating which included PAHs, aromatic amines, organoarsenic compounds. Due to the inherent multifunctional properties of PPY coatings, they can be used for extracting a wide array of analytes including -blockers in urine and serum samples [86], catechin and caffeine in t ea [87], aromatic compounds in aqueous samples [88], stimulants in human urine and hair samples [89], polar pesticides in water and wine

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25 samples [90], verapamil drug and its metabolit es [91], and Nnitrosamines in cell cultures [92]. Also, Lord and co-workers [93] have used polypyrrole coated SPME probe for in vivo pharmacokinetic studies in living animals. Polyanilines (PANI) are a class of conductive polymers that generally possess extended conjugated -electron system along a polym er backbone [94,95]. These are versatile materials in which analyte recognitio n can be achieved in different ways [96], including: (1) incorporation of counter ions that introduce se lective interactions; (2) via inherent multifunctionality (hydrophobic, acid–base and – interactions, polar functional groups, ion-exchange, hydroge n bonding, etc.) of the polymers; (3) introduction of functional groups to the m onomers. Djoznan and co-worker [97] used PANI coated gold wire for SPME of phenol and 4-chlorophenol from petrochemical sewage sample. Later, the same researchers also reported extraction of aliphatic alcohols from aqueous samples [98]. Some researchers have presented PANI film electrodeposited on the Pt wire for SPME of phenol derivativ es [99,100] and PAHs [101] from aqueous media. There are also reports of PANI film electrodeposited on the stainless steel wire for SPME of chloroand nitro benzenes [102], pht halates [103], aroma tic amines [104], and phenols [105] Although SPME has been introduced primarily for the extraction and preconcentration of organic compounds, it can be easily applied to the broad field of metal analysis by simply modifying the sorben t. Otu and Pawliszyn [106] reported use of PDMS coating modified with di-(2-ethylhe xyl)phosphoric acid (DEHP) (a liquid ionexchanger) for microextraction of bismuth (III) ion from an aqueous sample. Jia and co-

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26 workers [107] used dibenzo-18-crown-6 (D BC) doped membrane as SPME coating for extracting mercury (II) ions. A detection limit of 500 ng/L was repo rted in SPME-HPCLUV experiments. 1.4.2 Coatings used in in-tube SPME In the classical fiber format of SPME, th e fiber with sorbent coating on its end segment is installed in a specially designed SPME syringe. This design of the syringe offers good protection to the fibe r as well as the sorb ent coating on its external surface. However, fiber breakage, mechanical damage of the coating due to scraping and needle bending are the drawbacks frequently encountered by analytical chemists. Since, in fiber SPME, the length of the coated segment of the fiber is short (~ 1-2 cm), it provides low sorbent loading available for extraction. As a consequence, low sample capacity of the fiber imposes limitation on the extraction sensitivity of SPME. Thicker coatings may increase the sample capacity to some extent but long extraction tim e may become a major drawback in the whole extraction process. A nother major shortcoming of the fiber SPME is the difficulty to interface it with liquid-phase separation techniques (e.g., HPLC, CEC, etc). To overcome these format related shortcomings, in-tube SPME (or CME) was introduced [108]. In hyphenation with liquidphase separation technique, in-tube SPME can be easily automated which not only cuts down the total analysis time but also provides better accuracy and precision compar ed to manual operation. Coatings used in in-tube SPME can be compiled into two ma jor groups: (a) commerci al GC stationary

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27 phases used as in-tube SPME coatings and (b) tailor-made coatings for in-tube SPME. 1.4.2.1 Commercial GC stationary phases as in-tube SPME coatings Gas chromatographic stationary phases are suitable for use as in-tube SPME sorbents. Short pieces of coated GC capillary columns (in most cases, a 60-cm segment) are commonly used for in-tube SPME [109]. The stationary phase coating on the inner surface of the capillary serves as the extracting phase. Ta ble 1.2 lists frequently used extracting phases in in-tube SPME. Most of the sorbents used in in-tube SPME are commercially available GC stationary pha ses (e.g., DB-1, BP-1, SPB-1, SPB-5, PTE-5, Supelcowax, DB-5, Omegawax 250, DB-Wa x, BP-20 Wax, Supel-Q-PLOT etc.). Pawliszyn and co-workers first reporte d the use of in-tube SPME mode of microextraction in 1997 [16]. In their expe riments, 60-cm individual pieces of GC capillary columns with various stationa ry phases (Omegawax 250, SPB-1, SPB-5), and an uncoated fused silica capillary were used for extraction and each one of them was coupled to a commercial HPLC autosample r. Six phenylurea analytes were extracted using each of the above mentioned capillari es. The Omegawax 250, being the most polar phase, extracted the most and the uncoated fused silica capillary extracted the least of these polar analytes. SPB-1 and SPB-5 coa tings (nonpolar) also demonstrated poor extraction yield as was expected. Om egawax 250 GC capillary columns use poly(ethylene glycol) as the statio nary phase. It is the most frequently used sorbent in intube SPME for extracting polar analytes. Thus far, Omegawax 250 has been used for

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28 Table 1.2 Chemical structure and composition of GC stationary phases used in in-tube SPME Name of the phase Phase Composition Vendor References Chemical Structure BP-1 100% dimethyl polysiloxane SGE [110] SPB-1 100% dimethyl polysiloxane SUPELCO [111] DB-1 100% dimethyl polysiloxane JW [112] Si C H 3 CH3 O n PTE-5 Poly (5% diphenyl /95% dimethyl siloxane ) SUPELCO [113] SPB-5 Poly (5% diphenyl /95% dimethyl siloxane) SUPELCO [114] O Si O Si CH3 CH3 5% 95% Omega wax 250 Poly (ethylene glycol) SUPELCO [16] Supelco wax Poly (ethylene glycol) SUPELCO [113] DB-Wax Poly (ethylene glycol) JW [115] BP-20 Poly (ethylene glycol) SGE [114] HOCH2 CH2 O H n Supel-QPLOT Porous divinyl benzene polymer SUPELCO [116,117] CH2 CH2 n

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29 extracting phenylureas [16], blockers and its metabolites in urine and serum samples [118], carbamate pesticides [113,114,119], mu tagenic heterocyclic amines [111], ranitidine [108], and in drug analysis [120]. Although in both Supelcowax and Omegawax 250 coated capillaries, poly(ethyl ene glycol) was the common stationary phase, Omegawax 250 demonstrated higher yiel d in extracting carbamate from aqueous solution compared to the other [114]. In almost all of the above mentioned in-tube SPME publications SPB-1 (100% dimethyl polys iloxane), SPB-5 (poly 5% diphenyl/95% dimethyl polysiloxane), and uncoated fused silica capillary were used to study the importance of sorbent polarity in the extracti on of polar analytes. Takino and co-workers used DB-Wax (J&W Scientific, Folsom, CA, USA) for the determination of chlorinated phenoxy acid herbicides in environmental wa ter [115] and successfully coupled SPMELC with EI/MS providing enhanced selectiv ity and identification capability of the method. Tan and co-workers [110] have successf ully coupled in-tub e SPME to GC-FID. One-meter segments of BP-1 (100% methyl siloxane) and BP-20 ( polyethylene glycol) GC columns were used for the extraction of BTEX and phenols, respectively from aqueous media. Extraction was carried out by pushing the aqueous medium containing the analytes through the capillary using nitr ogen pressure. Desorption of the extracted analytes was done by using a small plug of or ganic solvent which carried the analytes from the capillary to the GC injection por t. Nardi [121,122] used capillaries (0.474 mm i.d., ~ 0.9 mm o.d.) statically coated with cross-linked PDMS gu m PS255 (a Petrarch Systems polydimethylsiloxane with ~ 1% vi nyl groups) for in-tube SPME of BETX from

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30 aqueous samples. The extracted analytes we re desorbed by connecting the extraction capillary (“capilla ry extractor”) as a precolumn through the polytetrafluoroethylene (PTFE) unions. To avoid carryover, analytes we re desorbed from extractor into GC for 3 min, under helium flow at room temperature. During this time analytes were focused quantitatively at the entrance of a laborat ory-made-cryofocusing device [123,124] that utilized a 0.32 mm i.d. transf er-line dipped into liquid ni trogen. Fast heating of the focusing transfer-line up to 200 C realized the BTEX injection. Although SPME has been developed to elimin ate the use of toxi c organic solvents in sample preconcentration step, a small amount of solvent was still used in the desorption process, particularly when coupl ed to LC. To reduce the amount of toxic organic solvent used in analyte(s) desorpti on step after the ex traction, Saito and coworkers [112] proposed a wire-i n-tube configuration of SPME in which a 20-cm piece of DB-1 (100% polydimethylsiloxa ne) coated capillary was us ed as the ex tractor. A stainless steel wire (diameter = 200 m) was in serted into the capilla ry (diameter B= 250 m) that significantly reduced the available in ternal volume of the capillary (9.82 L vs. 3.53 L) and thereby reduced the volume of so lvent required for desorption. The wire-intube SPME was successfully used to analyze antidepressant drugs in a urine sample. Another GC capillary column frequently used in in-tube SPME is Supel-Q-Plot. A porous divinylbenzene polymer is used as the st ationary phase in this column. Mester and co-workers [116] successfully coupled SPME to electrospray ionization mass spectrometry. A 60-cm piece of Supel-Q-PLOT column was used to preconcentrate and analyze trimethyland triethyll ead species from aqueous media. This system seems to be

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31 very promising in lead speciation. The same pha se has also been used for the analysis of endocrine disruptors in liquid medicines a nd intravenous solutions [125], daidzein and genistein in soybean foods [117], bisphenol A, alkylphenols, and phthalate esters in foods contacted with plastics [126]. 1.4.2.2 Tailor-made coatings for in-tube SPME Several tailor-made sorbents have found successful use in both fiberand in-tube SPME. Some of sorbents used for in-tube SPME include restricted access materials (RAMs), molecularly imprinted polymer s (MIPs), monolithic sorbents, and miscellaneous sorbents. 1.4.2.2.1 Restricted access materials Restricted access materials (RAMs) are special class of materials that prevent access of interferences (macromolecules) to the specific sorbent region where extraction and enrichment of low molecular weight analyte(s) take place [127]. Initially, these sorbents were developed for the isolation of low-molecular-mass drugs from biological fluids with minimum sample pretreatment and now they also find use in the isolation of herbicides from surface waters containing hi gh levels of humic substances [128]. Mullett and co-worker [129] reported use of a capillary packed with alkyl-diolsilica (ADS) restricted access material for the automated in-tube SPME of several benzodiazepines from human serum. The so rbent alkyl-diol-silica (ADS) possesses two

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32 different chemical layers (diol groups on th e outer layer, and alkyl groups on the inner layer) and a pore size that prevents larger mo lecules (e.g., proteins) from entering into the inner layer. Hydrophilic diol groups on the outer layer of the spherical ADS particles act like a filter to trap (and restrict) bulky molecules (e.g., proteins), whereas hydrophobic alkyl groups on the inner layer extract relatively smaller target analytes that easily penetrates the outer layer. In-tube SPME-HPLC-UV experi ments using ADS particles yielded detection limits of 22-29 ng/mL for various benzodiazepines. The same researchers have also reported use of alkyl-dio lsilica (ADS) restricted access material as the fiber SPME Coating for determination of benzodiazepines from human urine samples [130] and monitoring of drugs and metabolites in w hole blood [131]. 1.4.2.2.2 Molecularly imprinted polymers Molecularly imprinted polymers (MIPs) ar e cross-linked macromolecules with cavity-based specific binding site s for a target anal yte [132]. In order to obtain a highly selective recognition of a target molecule, a te mplate molecule (same or similar to target molecule) is incorporated in the mixture of reacting monomers during synthesis of MIP material. After completion of MIP synthesis, the template molecule is extracted out leaving a three dimensional imprint of itself in the form of a cavity in the polymer. Figure 1.4 illustrates different steps involved in molecular imprinting process [132]. Mullett and co-workers [133] reported the application of a molecularly imprinted polymer in in-tube SPME for selective extractio n of propranolol from biological fluids.

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33 Figure 1.4 Schematic representation of molecula r imprinting process. Reproduced from ref. [132] with permission.

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34 The propranolol-imprinted polymer particles were packed in a PEEK tubing (80-mm in length and 0.76-mm i.d.) and both the ends we re capped with a zero volume union fitted with 2-m frit. A detection limit of 0.32 g /mL was achieved for the extraction of propranolol from serum sample in in-t ube SPME-HPLC-UV experiments using MIPbased sorbent. Later, same researchers [134,135] also reported on line preparation of sample containing verapamil and its metabolites by an MIP material coupled on-line to a RAM precolumn. A detection limit of 5 ng/mL was obtained in LC-MS analysis. Koster and co-workers [136] have presented silica-bas ed SPME fibers coated with MIPs. In their work, clenbuterol-imprinted fibe rs were prepared and used in the selective extraction of brombuterol from human urine. The prepara tion of imprinted fibers was performed by silanization of silica fibers which were s ubsequently immersed in the polymerization solution composed of clenbuterol, methacrylic acid, ethylene glycol dimethacrylate, and azo(bis)isobutyronitrile dissolv ed in acetonitrile. Then, polym erization was performed for 12 h at 4 C under irradiation with UV light at 350 nm According to the authors, fibers with a polymeric film thickness of ~ 75 m were obtained in a reproducible manner. Recently, some researchers have also repor ted new molecularly imprinted SPME fibers for determination of triazines from environmental and food samples [137,138]. 1.4.2.2.3 Monolithic sorbents Commonly used open tubular extraction capillary cannot provide sufficient extraction efficiency since the ratio of its extraction coating volume to that of the

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35 capillary void volume is relatively small. On the other hand, capillaries with monolithic sorbents have greater phase ratio and provide the possibility of improving the extraction efficiency with shorter capillary. Monoliths can be synthesized in situ and provide structures with various func tional groups. Shintani and co-w orkers [139] demonstrated the use a C18-bonded monolithic capillary ( 450 mm 200 m i.d., silica skeleton size of ~ 3.0 m, with a through-pore size of 10 m and a meso-pore size of 12 nm) for in-tube SPME. The preconcentration of trace analytes (uracil, toluene naphthalene, biphenyl and fluorine) using the monolithic sorbent show ed ~ 50 times higher sensitivity than that using wall-coated capillary. Later, Feng’s re search group prepared monolithic capillaries based on poly(methacrylic acid-ethylene gl ycol dimethacrylate) [p(MAA-EGDMA)] and applied them to in-tube SPME–LC for the extraction of drugs from complex sample matrices, such as human body fluids [140-144] animal tissue [145] and food [140]. The hydrophobic polymer backbone structure and th e acidic pendant groups (from the MAA monomer) make this monolithic polymer suitabl e for extracting basic analytes, such as most of the drugs studied. Moreover, as some studies have reported [141,142], the biocompatibility of this monolithic structure allowed the direct analysis of biological samples with no other manipulation excep t dilution and/or centrifugation, which simplified the whole determination procedure. The same group [146] also synthesized a monolithic capillary based on poly(acrylamide-vinylpyridine-N, N’-methylene bisacrylamide), p(AA-VP-Bis). Figure 1.5 s hows the SEM images of the monolithic capillary. It was expected to show greates t ion-exchange interactions with acidic compounds through the pyridyl group. The re searchers confirmed this hypothesis by

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36 Figure 1.5 Scanning electron microscopic images of poly(AA-VP-Bis) monolithic capillary; (a) Wide-view and (b) close-up-v iew. Reproduced from ref. [146] with permission.

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37 using in-tube SPME–LC–UV to ex tract a group of analytes, including acidic drugs, and phenols. The extraction yield for 2,4-dinitr ophenol (the most acidic phenolic compound analyzed) was 87%, while for phenol (the l east acidic and least hydrophobic compound) it was 6%. 1.4.2.2.4 Miscellaneous sorbents In addition to the above mentioned sorbents, miscellaneous sorbents have been explored for in-tube SPME for extraction of various analytes. McComb and co-workers [147] introduced a novel method for the SPME of VOCs (e.g. BTEX) followed by GC analysis. In side needle capillar y absorption trap (INCAT) is a technique that uses a hollow needle with either a short length of GC capillary column placed inside it, or an internal coating of carbon, as the sample preconcentration phase. Sampling may be perfo rmed on ambient air, on solution, or on the sample solution headspace, by passing the gas or liquid through the device actively with a syringe, or passively via diffusion. In their work, one of the INCAT device had a 2.5 cm long GC capillary column (DB-5 TM) in serted in a 7.5 cm steel needle and other device was made by depositing carbon on inner su rface of steel needle which served as extraction phase for the preconcentration of VOCs. Their results suggested INCAT device may be used as a rapi d and sensitive method for the analysis of VOCs in both air and water samples. Saito and co-workers [148] developed a novel “fiber-in-tube” SPME method. To

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38 prepare the extraction tube, a heterocyclic po lymer, Zylon fiber was cut to 10 cm length and packed longitudinally into the same length of PEEK tube (0.25 mm i.d.). The diameter of each filaments of the fiber wa s about 11.5 m and the total number of the filaments packed in the PEEK tubing was about 280. The analysis of n-butyl phthalate of an actual wastewater was carried out with the newly developed fiber-in-tube SPME-LC system. The analytical determination of trace level phthalates in aqueous sample matrix has been regarded as one of the most im portant problems [149-152] With fiber-in-tube SPME preconcentration method the original con centration of phthalate in the wastewater was determined to be 0.40 ng/mL. The preconc entration factor of n-butyl phthalate was calculated as the ratio of the peak ar ea obtained with fi ber-in-tube SPME preconcentration and that without precon centration. The estimated preconcentration factor for n-butyl phthalate was about 160 with RSD less than 1% for repeated runs. Later same researchers developed an on-line fibe r-in-tube SPME-CE system using Zylon fiber for the separation of four trycylic antidepressants (amitriptyline, imipramine, nortriptyline and desipramine) [153]. 1.5 Parameters affecting extraction efficiency Although, in SPME, the physical and chemi cal properties of th e extracting phase (coating) mainly govern the extraction efficien cy, several other experimental parameters can also be manipulated to enhance the extraction efficiency. These experimental parameters include pH, stirring, heating, and addition of the salt to the sample matrix.

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39 1.5.1 Adjustment of sample matrix pH Most of the coatings used in SPME are elec trically neutral. Hence, these coatings are appropriate for (direct or headspace) extr action of analytes which remain neutral in the aqueous matrices. However, compounds su ch as organic acids and bases partially dissociate into ionic sp ecies in aqueous samples. In order to extract such compounds from aqueous media using SPME coatings, pH adjust ment of sample matrix is necessary to convert the ionic species into neutral molecules. Optimum pH of the matrix depends on the pKa or pKb values of organic acids and base s, respectively. In order to make sure that 99% of an organic acid is in neutral form, the pH of the matrix should be at least two units lower than pKa value of the acid [18]. Similarly, in case of a basic analyte, pH of the matrix should be at least two units larger than pKb value of the base [18]. 1.5.2 Agitation of the sample matrix Usually, agitation of the sample matrix is employed to reduce the extraction equilibrium time. In the direct extraction mode, the coated fiber is immersed into the sample matrix and the analytes are transporte d directly from the sample matrix to the extracting phase. Agitation of the sample matrix helps to accelerate analyte transport from the bulk of the liquid sample to the vici nity of the SPME fiber coating. Fast sample flow through the capillary (in-tube SPME), ra pid fiber or vial movement, stirring or sonication are also common methods used to decrease the extraction equilibrium time. Agitation minimizes the effect caused by so calle d “depletion zone” [18] formed close to

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40 the fiber as a result of fluid shielding and slow diffusion coeffi cients of analytes in liquid matrices. In the headspace extraction mode, ag itation of the aqueous sample generates a continuously fresh surface and ac celerates the mass transfer of less volatile analytes from the water to headspace. Once in the gaseous phase, analytes moves rapidly from the headspace to the extracting phase due to their la rge diffusion coefficients in the gas phase. 1.5.3 Heating of sample matrix In SPME, temperature has a significant impact on overall extraction efficiency. Although, the diffusion of the analyte increases with the incr ease in temperature leading to faster mass transfer from the liquid phase to the headspace and from the headspace to the coating, the coating/sample distributio n constant decreases with increase in temperature. Hence, the amount of analyte ex tracted at equilibrium would be lower at higher temperature. Simultaneous cooling of the coating can prevent the loss of extraction sensitivity. This idea was implemen ted by Zhang and co-w orkers [32] in the design of an internally cooled SMPE devi ce which allows simultaneous cooling of the sorbent while the sample matrix is heated [Figur e 1.6]. In this device, two concentric fused silica capillaries are used and the sorben t is coated on the outer surface of the larger diameter capillary. Liquid carbon dioxide is de livered via the inner capillary to the coated end of the outer capillary, resu lting in a coating temperature significantly lower than that of the sample matrix. This “cold finger” eff ect results in accumulation of the volatilized analytes at the tip of the fiber.

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41 Figure 1.6 Design of internally cooled SPME de vice. Reproduced from ref.[32] with permission.

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42 1.5.4 Addition of the salt to the sample matrix Addition of salt into the a queous sample matrix contai ning organic analytes (also called salting out) can significantly affect the extraction efficiency. Salting out is a well known phenomenon used to enhance extraction of organics from aqueous samples. Although, in SPME, sodium chloride (NaCl) sa lt is predominantly used, other salts (e.g., CaCl2, NH4Cl, (NH4)2SO4, MgSO4, Na2CO3, K2CO3) may also be utilized [154]. 1.6 Derivatization In organic analysis, the main challe nge involves the extr actions of polar compounds. The hydrophilic nature of polar compounds makes their extraction from environmental and biological matrices extr emely difficult. In such cases, various derivatization techniques are frequently used. Different derivatization approaches that can be implemented in combination with SPME ar e summarized in Figure 1.7 [155]. In direct derivatization, the deriva tizing agent is first added to the sample vial to convert the analyte(s) into a derivative followed by the extraction on the SPME fiber. In case of polar coatings, where the sorben t affinity toward target analytes is sufficient for extracting underivatized polar an alyte from aqueous phase, derivatization of the analytes may still be necessary to aid the separation and better chromatographic response. This can be achieved by employing in-coating derivatization following extraction. The most interesting and potentia lly very useful approach is simultaneous derivatization and extr action, performed directly on the coating [36]. This approach

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43 Figure 1.7 SPME derivatization techniques. Adapte d from ref. [155] with permission. Derivatization techniques in SPME Direct derivatization in sample matrix Derivatization in GC injection port Derivatization in SPME fiber coating Simultaneous derivatization and extraction Derivatization following extraction

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44 allows high efficiency and can be effectively used in remote field applications. In this case, the fiber is doped with a derivatizing re agent and subsequently is exposed to the sample. The analytes are extracted and si multaneously converted to compounds having high affinity for the coating.

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45 1.7 References to Chapter 1 [1] G. Vas, K. Vekey, J. Mass Spectrom. 39 (2004) 233. [2] R.M. Smith, J. Chromatogr. A 1000 (2003) 3. [3] J. Pawliszyn, Anal. Chem. 75 (2003) 2543. [4] F. Soxhlet, Dinger’s Polyt. J. 232 (1879) 461. [5] R.E. Majors, LC-GC Int. 10 (1997) 93. [6] B.E. Richter, B.A. Jones, J.L. Ezzel, N.L. Porter, N. Abdalovic, C. Pohl, Anal. Chem. 68 (1996) 1033. [7] A. Zlotorzynski, Crit. Rev. Anal. Chem. 25 (1995) 43. [8] K. Coulibaly, I.J. Jeon, Food Rev. Int. 12 (1996) 131. [9] S.B. Howthorne, Anal. Chem. 62 (1990) 633A. [10] M.M. Minnich, J.H. Zimmerman, B.A. Schumacher, J. AOAC Int. 79 (1996) 1198. [11] J.S. Fritz, Analytical Solid-Ph ase Extraction, Wiley–VCH, New York, 1999. [12] C.F. Poole, A.D. Gunatillekam, R. Sethuraman, J. Chromatogr. A 885 (2000) 17. [13] R.P. Belardi, J. Pawliszyn, Wa ter Pollut. Res. J. Can. 24 (1989) 179. [14] J. Pawliszyn, S. Liu, Anal. Chem. 59 (1987) 1475. [15] C.L. Arthur, J. Pawliszyn, Anal. Chem. 62 (1990) 2145. [16] R. Eisert, J. Pawlis zyn, Anal. Chem. 69 (1997) 3140. [17] S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Alli, A. Malik, Anal. Chem. 74 (2002) 752. [18] J. Pawliszyn, Solid Phase Microextr action: Theory and Practice, Wiley-VCH, New York, 1997.

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46 [19] J. Pawliszyn, Sampling and Sample Preparation for Field and Laboratory, Elsevier, New York, 2002. [20] Z. Zhang, J. Poerschmann, J. Pawliszyn, Anal. Commun. 33 (1996) 219. [21] Z. Zhang, M.J. Yang, J. Pawliszyn, Anal. Chem. 66 (1994) 844A. [22] C.L. Arthur, L.M. Killam, K.D. Buc hholz, J. Pawliszyn, J.R. Berg, Anal. Chem. 64 (1992) 1960. [23] G. Vas, K. Vekey, J. Mass Spectrom. 39 (2004) 233. [24] F.J. Santos, M.T. Galceran, D. Fraisse, J. Chromatogr. A 742 (1996) 181. [25] M. Chai, J. Pawliszyn, Envi ron. Sci. Technol. 29 (1995) 693. [26] R.-a. Doong, S.-m. Chang, Y.-c. Sun, J. Chromatogr. A 879 (2000) 177. [27] B. Shurmer, J. Pawliszyn, Anal. Chem. 72 (2000) 3660. [28] A. Saraullo, P.A. Martos, J. Pawliszyn, Anal. Chem. 69 (1997) 1992. [29] B. Schafer, P. Hennig, W. Engewal d, J. High Resolut. Chromatogr. 20 (1997) 217. [30] I. Valor, C. Cortada, J.C. Molt o, J. High Resolut. Ch romatogr. 472 (1996) 472. [31] J. Dugay, C. Miege, M.C. Hennion, J. Chromatogr. A 795 (1998) 27. [32] Z. Zhang, J. Pawliszyn, Anal. Chem. 67 (1995) 34. [33] K.D. Buchholz, J. Pawliszyn, Environ. Sci. Technol. 27 (1993) 2844. [34] E. Matisova, J. Sedlakova, M. Sl ezackova, T. Welsch, J. High Resolut. Chromatogr. 22 (1999) 109. [35] H.H. Jelen, K. Wlazly, E. Wasowicz, E. Kaminski, J. Agric. Food Chem. 46 (1998) 1469. [36] L. Pan, M. Adams, J. Pawliszyn, Anal. Chem. 67 (1995) 4396. [37] C. Wijesundera, L. Drury, T. Wals h, Aust. J. Dairy Technol. 53 (1998) 140. [38] H. Van Doom, C.B. Grabanski, D.J. Miller, S.B. Hawthorne, J. Chromatogr. A 829 (1998) 223.

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47 [39] Y.-C. Wu, S.-D. Huang, Anal. Chem. 71 (1999) 310. [40] M.R. Lee, Y.C. Yeh, W.S. Hsia ng, B.H. Hwang, J. Chromatogr. A 806 (1998) 317. [41] P. Bartak, L. Cap, J. Chromatogr. A 767 (1997) 171. [42] K. Jinno, T. Muramatsu, Y. Saito, Y. Kiso, S. Magdic, J. Pawliszyn, J. Chromatogr. A 754 (1996) 137. [43] C.G. Zambonim, F. Palmisano, Analyst 123 (1998) 2825. [44] A. Penalver, E. Pocurull, F. Borrull, R.M. Marce, TrAC, Trends Anal. Chem. 18 (1999) 557. [45] M.D.F. Alpendurada, J. Chromatogr. A 889 (2000) 3. [46] S. Mitra, Sample Preparation T echniques in Analytical Chemistry, WileyInterscience, Hoboken, NJ, 2003. [47] V. Mani, Applications of Solid Phase Microextraction, Royal Society of Chemistry, Cambridge, UK, 1999. [48] S.A.S. Wercinski, Solid Phase Microe xtraction, Mercel Dekk er Inc., New York, 1999. [49] R.E. Shirey, V. Mani, in Pittcon 1997, Atlanta, GA, 1997. [50] B.J. Hall, J.S. Brodbelt, J. Chromatogr. A 777 (1997) 275. [51] S. Tumbiolo, J.-F. Gal, P.-C. Maria, O. Zerbinati, Anal. Bioanal. Chem. 380 (2004) 824. [52] J.A. Lloyd, P.L. Edmiston, J. Forensic Sci. 48 (2003) 130. [53] D. Zuba, A. Parczewski, M. Reic henbacher, J. Chromatogr. B 773 (2002) 75. [54] R. Aranda, P. Kruss, R.C. Burk, J. Chromatogr. A 888 (2000) 35. [55] D. Poli, E. Bergamaschi, P. Manini, R. Andreoli, A. Mutti, J. Chromatogr. B 732 (1999) 115.

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48 [56] B. Rega, N. Fournier, E. Guic hard, J. Agric. Food. Chem. 51 (2003) 7092. [57] O. Ezquerro, M.T. Tena, J. Chromatogr. A 1068 (2005) 201. [58] F. Mangani, R. Cenciari ni, Chromatographia 41 (1995) 678. [59] D. Djozan, Y. Assadi, Chromatographia 45 (1997) 183. [60] D. Djozan, Y. Assadi Microchem. J. 63 (1999) 276. [61] M.A. Farajzadeh, A.A. Matin, Anal. Sci. 18 (2002) 77. [62] M.A. Farajzadeh, M. Hatami Chromatographia 59 (2004) 259. [63] J. Jia, X. Feng, N. Fang, Y. Wang, H. Chen, W. Dan, J. Environ. Sci. Health 37 (2002) 489. [64] M. Giardina, S.V. Olesik, Anal. Chem. 73 (2001) 5841. [65] M. Giardina, S.V. Olesik, Anal. Chem. 75 (2003) 1604. [66] M. Giardina, L. Ding, S.V. Ol esik, J. Chromatogr. A 1060 (2004) 215. [67] Y. Liu, M.L. Lee, J.K. Hageman, Y. Yang, S.B. Hawthorne, Anal. Chem. 69 (1997) 5001. [68] Y. Liu, Y. Shen, M.L. Lee, Anal. Chem. 69 (1997) 190. [69] J. Hou, Q. Ma, X. Du, H. Deng, J. Gao, Talanta 62 (2004) 241. [70] D. Djozan, Y. Assadi, S.H. Haddadi, Anal. Chem. 73 (2001) 4054. [71] M.A. Farajzadeh, M. Hatami, J. Sep. Sci. 26 (2003) 802. [72] F. Guo, T. Gorecki, D. Irish, J. Pawliszyn, Anal. Commun. 33 (1996) 361. [73] D. Djozan, M. Amir-Zehni, Chromatographia 58 (2003) 221. [74] D. Djozan, Y. Assadi, G. Kari m-Nezhad, Chromatographia 56 (2002) 611. [75] S. Li, S.G. Weber, Anal. Chem. 69 (1997) 1217. [76] T. Gorecki, P. Martos, J. Pawliszyn, Anal. Chem. 70 (1998) 19.

PAGE 76

49 [77] C. Xiao, S. Han, Z. Wang, J. Xi ng, C. Wu, J. Chromatogr. A 927 (2001) 121. [78] K. Jinno, K. Yamamoto, J.C. Fetzer, W.R. Biggs, J. Micr ocol. Sep. 4 (1992) 187. [79] D.L. Stalling, C.Y. Guo, S. Sa im, J. Chromatogr. Sci. 31 (1993) 265. [80] R.V. Golovnya, M.B. Terenina, E.L. Ruchkina, V.L. Karnatsevich, Mendeleev. Commun. 6 (1993) 231. [81] A. Glausch, A. Hirsch, I. Lamparth, V. Schurig, J. Chromatogr. A 809 (1998) 252. [82] P.F. Fang, Z.R. Zeng, J.H. Fan, Y.Y. Chen, J. Chromatogr. A 867 (2000) 177. [83] S.D. Harvey, D.A. Nelson, B.W. Wright J.W. Grate, J. Chromatogr. A 954 (2002) 217. [84] J. Wu, Z. Deng, J. Pawliszyn, in Extech.’99, Waterloo, Canada, 1999. [85] J. Wu, J. Pawliszyn, J. Chromatogr. A 909 (2001) 37. [86] J. Wu, H.L. Lord, J. Pawliszyn, H. Kataoka, J. Microcol. Sep. 12 (2000) 255. [87] J. Wu, W. Xie, J. Pawliszyn, Analyst 125 (2000) 2216. [88] J. Wu, J. Pawliszyn, Anal. Chem. 73 (2001) 55. [89] J. Wu, H. Lord, J. Pawliszyn, Talanta 54 (2001) 655. [90] J. Wu, C. Tragas, H. Lord, J. Pa wliszyn, J. Chromatogr. A 976 (2002) 357. [91] M. Walles, W.M. Mullett, K. Levsen, J. Borlak, G. Wunsch, J. Pawliszyn, J. Pharm. Biomed. Anal. 30 (2002) 307. [92] W.M. Mullett, K. Levsen, J. Borlak, J. Wu, J. Pawliszyn, Anal. Chem. 74 (2002) 1695. [93] H.L. Lord, R.P. Grant, M. Walles, B. Incledon, B. Fahie, J. Pawliszyn, Anal. Chem. 75 (2003) 5103. [94] A. Kraft, Conducting polymers; Or ganic Molecular Solids: Properties and Applications, CRC Press, Boca Raton, FL, 1997. [95] R.A. Pethrick, Conducting polymers; Desk Reference of Functional Polymers: Synthesis and Applicatio ns, ACS, Washington, DC, 1997.

PAGE 77

50 [96] H. Bagheri, M. Saraji, J. Chromatogr. A 986 (2003) 111. [97] D. Djozan, S. Bahar, Chromatographia 58 (2003) 637. [98] D. Djozan, S. Bahar, Chromatographia 59 (2004) 95. [99] H. Bagheri, A. Mir, E. Babanezhad, Anal. Chim. Acta. 532 (2005) 89. [100] M. Mousavi, E. Noroozian, M. Jalali-H eravi, A. Mollahosseini, Anal. Chim. Acta. 581 (2007) 71. [101] H. Bagheri, E. Babanezhad, A. Es -haghi, J. Chromatogr. A 1152 (2007) 168. [102] X. Li, J. Chen, L. Du, J. Chromatogr. A 1140 (2007) 21. [103] X. Li, M. Zhong, S. Xu, C. Sun, J. Chromatogr. A 1135 (2006) 101. [104] M. Huang, T. Chao, Q. Zhou, G. Jiang, J. Chromatogr. A 1048 (2004) 257. [105] M. Huang, G. Jiang, Y. Cai, J. Sep. Sci. 28 (2005) 2218. [106] E.O. Otu, J. Pawliszyn, Microchim. Acta 112 (1993) 41. [107] C. Jia, Y. Luo, J. Pawlis zyn, J. Microcol. Sep. 10 (1998) 167. [108] H. Kataoka, H.L. Lord, J. Pa wliszyn, J. Chromatogr. B 731 (1999) 353. [109] H.L. Lord, J. Pawliszyn, LC-GC (1998) 41. [110] B.C.D. Tan, P.J. Marriott, P.D. Morrison, H.K. Lee, Analyst 124 (1999) 651. [111] K. Kataoka, J. Pawliszy n, Chromatographia 50 (1999) 532. [112] Y. Saito, Y. Nakao, M. Imaizumi, Y. Mo rishima, Y. Kiso, K. Jinno, Anal. Bioanal. Chem. 373 (2002) 81. [113] Y. Gou, J. Pawliszyn, Anal. Chem. 72 (2000) 2774. [114] Y. Gou, R. Eisert, J. Paw liszyn, J. Chromatogr. A 873 (2000) 137. [115] M. Takino, S. Daishima, T. Nakahara, Analyst 126 (2001) 602.

PAGE 78

51 [116] Z. Mester, J. Pawliszyn, Rapi d Commun. Mass Spectrom. 13 (1999) 1999. [117] K. Mitani, S. Narimatsu, H. Kataoka, J. Chromatogr. A 986 (2003) 169. [118] H. Kataoka, S. Narimatsu, H.L. Lord, J. Pawliszyn, Anal. Chem. 71 (1999) 4237. [119] Y. Gou, C. Tragas, H. Lord, J. Pa wliszyn, J. Microcol. Sep. 12 (2000) 125. [120] H. Kataoka, H.L. Lord, S. Yamamoto, S. Narimatsu, J. Pawliszyn, J. Microcol. Sep. 12 (2000) 493. [121] L. Nardi, J. Ch romatogr. A 985 (2003) 39. [122] L. Nardi, J. Ch romatogr. A 985 (2003) 85. [123] L. Nardi, in P. Sandra (Editor), 25th International Symposium on Capillary Chromatography, Riva del Garda, Italy, May 13-17 (2002), p. on CD. [124] L. Nardi, J. Ch romatogr. A 985 (2003) 67. [125] K. Mitani, S. Narimatsu, F. Izushi, H. Kataoka, J. Pharm. Biomed. Anal. 32 (2003) 469. [126] H. Kataoka, M. Ise, S. Narimatsu, J. Sep. Sci. 25 (2002) 77. [127] W.M. Mullett, J. Pawliszyn, J. Sep. Sci. 26 (2003) 251. [128] C.F. Poole, TrAC, Trends Anal. Chem. 22 (2003) 362. [129] W.M. Mullett, K. Levsen, D. Lubda, J. Pawliszyn, J. Chromatogr. A 963 (2002) 325. [130] W.M. Mullett, J. Pawliszyn, Anal. Chem. 74 (2002) 1081. [131] M. Walles, W.M. Mullett, J. Pa wliszyn, J. Chromatogr. A 1025 (2004) 85. [132] K. Haupt, Analyst 126 (2001) 747. [133] W.M. Mullett, P. Martin, J. Pawliszyn, Anal. Chem. 73 (2001) 2383. [134] W.M. Mullett, M. Walles, K. Levsen, J. Borlak, J. Pawliszyn, J. Chromatogr. B 801 (2004) 297.

PAGE 79

52 [135] M. Walles, W.M. Mullett, K. Levsen, J. Borlak, G. Wunsh, J. Pawliszyn, J. Pharm. Biomed. Anal. 30 (2002) 307. [136] E.H.M. Koster, C. Crescenzi, W. den Hoedt, K. Ensing, G.J. de Jong, Anal. Chem. 73 (2001) 3140. [137] E. Turiel, J.L. Tadeo, A. Mart in-Esteban, Anal. Chem. 79 (2007) 3099. [138] X. Hu, Y. Hu, G. Li, J. Chromatogr. A 1147 (2007) 1. [139] Y. Shintani, X. Zhou, M. Furuno, H. Mi nakuchi, K. Nakanishi, J. Chromatogr. A 985 (2003) 351–357. [140] J.-F. Huang, B. Lin, Q.-W. Yu, Y. -Q. Feng, Anal. Bioanal. Chem. 384 (2006) 1228. [141] Y. Fan, Y.-Q. Feng, S.-L. Da, Z.-G. Shi, Anal. Chim. Acta. 523 (2004) 251. [142] Y. Fan, Y.-Q. Feng, S.-L. Da, X.-P. Gao, Analyst 129 (2004) 1065. [143] Y. Wen, Y. Fan, M. Zhang, Y.-Q. Feng, Anal. Bioanal. Chem. 382 (2005) 204. [144] Y. Fan, Y.-Q. Feng, J.-T. Zhang, S.-L. Da, M. Zhang, J. Chromatogr. A 1074 (2005) 9. [145] J. Nie, Q. Zhao, J. Huang, B. Xi ang, Y.-Q. Feng, J. Sep. Sci. 29 (2006) 650. [146] Y. Fan, M. Zhang, Y.-Q. Feng, J. Chromatogr. A 1099 (2005) 84. [147] M.E. McComb, R.D. Oleschuk, E. G iller, H.D. Gesser, Talanta 44 (1997) 2137. [148] Y. Saito, Y. Nakao, M. Imaizumi, T. Ta keichi, Y. Kiso, K. Jinno, Fresen. J. Anal. Chem. 368 (2000) 641–643. [149] K. Furtmann, Fresen. J. Anal. Chem. 348 (1994) 291–296. [150] K. Furtmann, Anal. Methods. Inst. 5 (1995) 254–265. [151] X.-P. Lee, T. Kumazawa, K. Sato, O. Suzuki, J. Chromatogr. Sci. 35 (1997) 302– 308. [152] S. Ulrich, J. Martens, J. Chromatogr. B 696 (1997) 217–234.

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53 [153] K. Jinno, M. Kawazoe, Y. Saito, T. Takeichi, M. Hayashida, Electrophoresis 22 (2001) 3785–3790. [154] T. Kumazawa, X.-P. Lee, K. Sato, O. Suzuki, Anal. Chim. Acta 492 (2003) 49. [155] L. Pan, J. Pawliszyn, Anal. Chem. 69 (1997) 196.

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54 CHAPTER 2 SOL-GEL TECHNOLOGY IN SOLI D-PHASE MICROEXTRACTION AND CAPILLARY MICROEXTRACION 2.1 Sol-gel Technology: A brief history The term sol-gel process [1] has been us ed for any solution involving hydrolysis of a precursor and formation of a gel via polycondensation reactions. Sol-gel technology offers a simple but versatile approach to th e synthesis of inorgani c polymers and hybrid inorganic-organic materials. Due to unique combinations of properties and numerous inherent advantages such as better hom ogeneity and purity, easier controllability, enhanced manageability, sol-gel technology has found growing interest in diverse research areas. The history of sol-gel technology dates back to mid-1800s. In 1845, Ebelman [2] prepared tetraethoxysilane (TEOS) from silic on tetrachloride (SiCl4) and ethanol. His subsequent publications [3,4] document the hydrolysis of TEOS to yield silicate solutions from which fibers could be drawn and th e casting of amorphous gels. In late 1850s, Mendeleyev [5] conceived of the novel idea th at hydrolysis of SiCl 4 yields a product tetrahydroxysilane (Si(OH)4) th at undergoes polycondensati on reactions to form high molecular weight polysiloxanes. After almost a century later, Hurd [6] showed a polymeric structure of silicic acid, which was widely accepted for the demonstration of

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55 the network structure of silica gels. Geffcken [7] used alkoxid es to prepare oxide films. During 1950s and 1960s Roy and coworkers [8,9] succeeded in using sol-gel methods to synthesize a large number of novel ceramic oxide compositions involving Al, Si, Ti, Zr, etc., that were impossible to obtain us ing ceramic powder methods. Stober and coworkers [10] reported in 1968 that both the morphology and size of the powders could be controlled using ammonia as a catalyst for th e TEOS hydrolysis reaction. In early 1970s, Dislich [11], and Levene and Thomas [12] independently developed multicomponent glasses using alkoxide precursors and co ntrolling the sol-gel hydrolysis and polycondensation reactions. J.D. Mackenzie [13] has divided the achie vements in sol-gel chemistry during last two and a half decades into two broader generations: (1) first generation and (2) second generation sol-gel process. The first gene ration sol-gel process involved in better understanding of the structure and physical chemistry of th e “original-type” of liquid solution ( mixture of alcohol, alkoxide, water, catalyst) which resulted in oxide gels. The pioneering work of Schmidt at the Fraunhoffer Institut e [14,15] who successfully incorporated organic material into inorganic network by sol-ge l process is regarded as the beginning of second generati on by J.D. Mackenzie. Schmid t’s invention opened up a new possibility of creating hybrid organic-inorganic materials us ing a very simple sol-gel approach. Schmidt’s work opened a new chapter in sol-gel chemistry. Cortes and coworkers [16] created porous monolithic ceramic beds within small-diameter capillaries using sol-gel technology by polymerizing soluti ons containing potassium silicate for its

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56 application in liquid chromat ography (LC) as a separation column. Later, Crego and coworkers [17] reported the preparation of so l-gel open tubular capillary columns (OTCs) for reversed-phase liquid chromatography (R PLC). Guo and Colon [18] developed a solgel stationary phase for open tubular elec trochromatography (OTEC). Few years later, Malik and coworkers introduced sol-ge l coated capillary columns for gas chromatography (GC) [19], and sol-gel coated fibers for solid-phase microextraction (SPME) [20]. Among many scientists working in the field of chromatography, Tanaka and co-workers made a significant contribu tion by developing sol-gel monolithic beds and using them in high-performance liquid chromatography (HPLC) columns [21-23]. They showed high permeability and high column efficiency of monolithic beds compared to a particle-packed column (most commonly used in HPLC). 2.2 Reactions involved in the sol-gel process In order to control the entire sol-gel proces s and fine-tune the properties of the target product, it is important to understand the chemical reactions involved (scheme 2.1). In general, a sol-gel process involves hydrolys is of metal alkoxides precursors (and/or polymers) and polycondensation reactions conver ting them into a colloid that ultimately turns into a three dimensional network. Figur e 2.1 illustrates various aspects of the solgel process. As can be seen in figure 2.1, any experimental pa rameter that a ffects sol-gel reactions is likely to influen ce the properties of the final product. Hence, accurate control of experimental conditions is very important in sol-gel synthe sis. The relative rates of

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57 Hydrolysis reaction: n H2O M ( OR) xM ( OR) x n ( OH) n n ROH Condensation reaction: M HO M H2O M M O OH and/or M HO M ROH M M O OR where, M is a metal atom (e.g., Si, Al, Ti, Zr, Ge, W, etc.). R is an alkyl group. Scheme 2.1 Key reactions in the sol-gel process ad apted from ref. [1] with permission.

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58 Figure 2.1 Overview of the sol-gel process. Repr oduced from ref. [1] with permission.

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59 hydrolysis and condensation may vary depending on experimental conditions. When the rate of condensation reaction is higher than that of the hydrolysis reaction, the resulting sol-gel material is highly branched and the corresponding gel typically acquires a mesoporous structure [24]. On the other hand, if the hydrolysis reaction rate is significantly higher than that of the condensation reaction, then the resulting sol-gel material is weakly branched and the corresponding gel ty pically acquires a microporous structure [25]. A typical sol solution gene rally contains the following chemical components: (1) one or more sol-gel precurso r(s) (usually a metal alkoxide M(OR)x), (2) solvent system, (3) a catalyst (an aci d, base or fluoride), and (4) water. Since hydrolysis and condensation both i nvolve nucleophilic displacement (SN) mechanism, the reactivity of metal alkoxides in the sol-gel process, consisting of these reactions, is dependent on the positive partial charge of the metal atom and its coordination number. In general, the longer a nd bulkier the alkoxide group attached to a particular metal atom, the less reactive that precursor is in hydrolysis and condensation [26,27]. Many metals, such as titanium, alum inum, vanadium, zirconium, and germanium, can be used to prepare their alkoxides. Ho wever, silica-based alkoxides are the most widely used precursors due to their well known chemistry, stability of Si-O bond, and commercially availability of starting materials [28]. Along with the sol-gel precurs or(s), catalyst(s), and wate r, the sol solution also contains sol-gel active organic ligands incl uding polymer(s). To accommodate all these chemical ingredients, a solvent system is chosen in such a way that it provides a homogeneous system, does not hinder the solgel process, and avoids any undesired side

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60 reactions. Often more than one solvent (e.g., mixture of methanol and dichloromethane) is used depending on the compa tibility of the sol-gel precursor(s) and the sol-gel active organic ligand. The amount of so lvent used also has a signif icant effect on the gelation time. Besides, the water-to-precursor ratio in the sol solution may also affect the reaction rates as well as the physical properties of the created sol-gel materials. Among all the chemical ingredients used in sol gel process, cata lyst(s) play a vital role. They not only change the reaction speed, the type of the catalyst also affects the structure of the resulting sol-gel material s. Various acidic (e .g., acetic acid [29], hydrofluoric acid [30], and trif luoroacetic acid [31] and ba sic ammonia [32] and amines [33] catalysts have been used to expedi te the alkoxide-based sol-gel processes. A generally accepted notion is that acid-catalyzed sol-gel processes are more likely to produce linear polymers because under acidic conditions, the hydrolysis of alkoxide precursors is faster than the condensati on process [34]. Under acidic conditions, the mechanism of hydrolysis reaction involves pr otonation of the alkoxide group followed by a nucleophilic attack by water to form a pentac oordinate intermediate (scheme 2.2 A) [1]. On the other hand, under basic condition, condensation reaction is faster and the rate of the overall sol-gel process is determined by the relatively slow hydrolysis step. The hydrolysis reaction under basic condition is beli eved to start with the nucleophilic attack on the silicon atom by the hydroxide anion an d form a penta-coordinated intermediate. This step is followed by the substitu tion of an alkoxide group by a hydroxyl group (scheme 2.2 B) [1,35,36].

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61 1. Hydrolysis mechanism SiOR RO RO O R H+H2O SiO RO RO OR O H H HR Si RO RO OR OH HOR H+ 2. Condensation mechanism R -S i (OH)3 H+ R -S i (OH)2O H H R-Si(OH)2O H H R-Si(OH)3 Si OH OH R O Si OH OH R H3O + Scheme 2.2-A Mechanism of acid catalyzed sol-gel r eactions. Adapted from ref. [1] with permission.

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62 1. Hydrolysis mechanism Si OR RO RO RO HOSi O R RO OR HO OR Si OR OR HO OR RO2. Condensation mechanism R -S i (OH)3 OHR-Si(OH)2OH2O R-Si(OH)2OR-Si(OH)3 R-Si(OH)2-O-Si(OH)2R OHScheme 2.2-B Mechanism of base catalyzed sol-gel reactions. Adapted from ref. [1] with permission.

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63 2.3 Steps involved in preparation of sol-gel coated SPME fiber and CME capillary The organic-inorganic hybrid materials synthesized by sol-ge l technology have been used as stationary phases in various separation techniques such as gas chromatography [19], high-performance li quid chromatography [18,23,37], and capillary electrochromatography [18,38]. Preparation of the sol-gel sorbent co ated fiber/capillary involves design and preparation of the sol solu tion, pretreatment and coating of the fusedsilica fiber/capillary. 2.3.1 Design and preparation of sol solution The most decisive step in the preparati on of a sol-gel coating for both fiber SPME and CME is the design of the sol solution. Th e successful creation of the desired sol-gel sorbent depends upon the selection of the so l solution ingredients. The sol solution ingredients typically include i norganic precursor(s), a solvent system, a catalyst, water, a sol-gel active organic polymer, and a surface deactivating agent. Among various catalysts, trifluoroacetic acid (TFA) is the most commonly used catalyst in the preparation of solgel SPME and CME coatings. TFA (a relativ ely strong organic acid) along with low concentrations of water (usually 5-10 %) also serves as a controlled source of water for the sol-gel hydrolysis reaction. A reasonable gelation time (1-2 h) is usually achieved by adjusting the amount water and acid catalyst. Along with sol-gel precursor(s), sol-gel active organic ligands (polymer or monomers) with specific functional groups are added to sol solution to provide desired sorbent sele ctivity toward target analytes. In sol-gel

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64 SPME and CME coatings, a surface deactiva ting reagent may be used to deactivate residual silanol groups on the sorbent surface. Malik and coworkers have reported the use of various deactivation reagents, such as phenyldimethylsilane (PheDMS) [39,40], poly(methylhydrosiloxane) (PMHS) [19,20,4144], and 1,1,1,3,3,3-hexamethyldisilazane (HMDS) [41-45]. 2.3.2 Pretreatment, coating, and post-coati ng treatment of fused silica SPME fiber/capillary SPME fibers are solid cylindrical rods with no flow-through holes and have small diameters (~ 100 m). However, capillaries used in CME (also known as in-tube SPME) differ from a fiber by the presence of a flow-through hole (Figure 2.2). Due of its mechanical strength and chemical inertness, fused silica material is commonly used as the substrate for both fiber-based and capillary-based SPME device. The commercially available fused silica capillaries have a protect ive polyimide coating on the outer surface. This polyimide coating protects the fused silica substrate from micro scratches during handling and storage. A sorbent coating is appl ied to the outer surface of the fiber (fiberSPME) or to the inner surface of th e capillary (CME or in-tube SPME). The main purpose of pretreatment of the fi ber (outer surface) or capillary (inner surface) is to enhance the silanol (Si-OH) cont ent of the surface, and thereby facilitate the effective bonding of the sol-gel sorbent (coa ting or monoliths) materials to the fused silica substrate. In the case of fiber-based SPME, first the protective polyimide coating is

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65 Figure 2.2 Schematics illustrating the cross sectional views of sorbent-coated SPME fiber (A), and sorbent-coated capillary CME (B). Adapted from ref. [46] with permission. Fused silica capillary Fused silica fiber Solid (no hole) SPME coating CME coating ( A ) ( B )

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66 removed from the outer surface of the fiber (1 -cm segment) at one of its ends by either burning off the external polyimide protective coating using flame or by dipping the fiber end into a suitable organic so lvent (e.g., acetone) for severa l hours. After drying, bare segment of the fiber is dipped into a 1.0 M NaOH solution followed by thorough rinsing with water before dipping into a 0.1 M HCl solution to expose a maximum number of silanol groups on the surface of the fiber. Late r, the treated surface is rinsed with copious amounts of water and dried. The pretreated fibe r end is then dipped (approximately 20-30 min) in appropriately designed sol-gel coating solution [20]. Th is step is usually repeated number of times until the desired coating thickness is achieved. This sol-gel coating strategy was used and customized by other SPM E research groups [47-49]. Subsequently, the fiber is removed from the solution and thermally conditioned under helium or nitrogen in the GC injection port. For CME, the same treatment may be a pplied to the inner surface of the fused silica capillary. However, Hayes and Ma lik [50] have described a method of hydrothermal pre-treatment of the fused-si lica capillary. For this, a homemade gas pressure-operated capillary filling/purging device was used for rinsing and coating processes as shown in Figure 2.3. First, the fuse d silica capillary is rinsed with different organic solvents (e.g., CH2Cl2, CH3OH, etc.) to clean the capillary inner surface off any organic contaminants. For hydrothermal trea tment, deionized water is pushed through entire capillary length under helium pressure (50 psi) for a predetermined period of time (e.g., 15 minute). The deionized water is th en expelled from the capillary under helium pressure leaving behind a thin layer of water on the inner su rface of the capillary. Both

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67 Figure 2.3 Schematic of a homemade capillary filling/purge device. Adapted from ref. [51] with permission. Gas flow inlet Flow control valves Fused silica capillary Gas flow outlet Pressurized chamber Vial containing sol-gel coating solution Threaded detachable cap

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68 ends of the capillary are then sealed with a high-temperat ure flame (e.g., an oxyacetylene torch), and the sealed capillary is conditioned in a GC oven at 250 C for two hours. Under these conditions, additi onal silanol groups are gene rated on the fused silica capillary surface as a result of the hydrolysis of siloxane bridges. To moderate the surface silanol concentration, both ends of the capillary are cut open and the thermal treatment is continued for an additional two hours, by simultaneously heating the capillary while purging with helium. The hydrothermal tr eatment also provides a more uniform distribution of these silanol groups on the surface facilitatin g strong chemical anchoring of the sol-gel surface coating/monolithic bed th at will subsequently be created within the capillary. To prepare sol-gel coated CME capi llary, a hydrothermally treated fused silica capillary is filled with previously designe d sol solution [51] using home-made capillary filling/purging device described earlier (Figure 2.3). The sol solution is kept inside the capillary for a desired period of time (~ 15-30 min) to facilita te the formation of a sol-gel coating, and its chemical bonding to the capillar y inner walls. After this, the unbonded portion of the sol solution is expelled from th e capillary, under helium pressure (~ 50 psi) leaving behind a surface-bonded sol-gel coating within the capillary. The sol-gel coating is then purged with helium for additional pe riod of time (~ 30 min) to evaporate any remaining volatile organic solvents. Later, thermal conditioning is carried out in a GC oven by temperature-programmed heating of the coated capillary. Usually, the final conditioning temperature is determined by thermal stability of organic component (functional group(s) and side-cha in(s)) used to prepare the so rbent coating. After thermal conditioning, the extraction capil lary is further rinsed w ith organic solvents (e.g., CH2Cl2,

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69 CH3OH) to clean the coated surface and conditioned again in the GC oven. The conditioned capillary is then cu t into small pieces (~ 10-12 cm ) that are used to perform capillary microextraction. 2.4 Characterization and morphology of sol-gel sorbents The performance of sol-gel organic-i norganic hybrid SPME and CME coatings depend on the characteristics of the sol solution ingredients used to pr epare such coatings. To study the chemical bonds in sol-gel structure, spectroscopic techniques like Fourier transform infrared spectroscopy (FTIR) [ 52,53], and nuclear magne tic resonance (NMR) [54-56], fluorescence spectroscopy [ 53] are frequently used. In frared (IR) spectroscopy is an important and simple tool to follow th e evolution of the sol-gel material and microstructure of sol–gel s ilica films [57,58]. In sol-gel SPME, FTIR spectroscopy is most commonly used to identify specific chemical bonds (Table 2.1) on the sorbent coating [59,60]. Another powerful analytical technique, nuclear magnetic resonance (NMR), was used by Rodriguez and Colon [61] to investigate the species present in the sol-gel solution used to modify the inne r surface of an open tubular CEC column. To study the detailed surface morphology of the sol-gel materials, scanning electron microscopy (SEM) is a powerful tool. With SEM, sample surface is scanned by a fine electron incident beam which produces an image with great depth of field and an almost three-dimensional appearance. With th is feature, SEM is the most widely used technique to evaluate the morphology of sol-gel material s [40,50,62,63]. In case of sol-

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70 Table 2.1 Characteristic Infrared bands in spectra of sol-gel materials Type of bond Wavelength (cm-1) References Si-OH 940-950 [64] Si-O-C 1153–1159 [65,66] Zr-O-Si 945-980 [67,68] Si-O-Si 1000-1200 [69-71] Si-O-Al 900-920 [72] Si-O-Ti 940-960 [69,73]

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71 gel SPME and CME, SEM helps to study su rface structural details through cross sectional and surface views of sol-gel fiber/ capillary coating. It can also reveal the uniformity of coating thickness and st ructural defects if any [41]. 2.5 Sol-gel sorbents used in SP ME and CME: A brief overview Sol-gel technology for fused silica fibe r/capillary-based SPME offers many advantages over SPME with conventional coat ings. Sol-gel coating procedure allows creation of chemical bonds between the fuse d silica surface and the sorbent coating through condensation of silanol and other sol-gel active groups. It provides surfacecoatings with both thermal and solvent stabil ity ensuring reproducible performance of the sorbent coatings. High thermal stability of the sol-gel coa ting provides an opportunity to broaden the applicability of SPME and CME toward analytes with high-boiling point. The solvent stability of sol-gel coatings makes sol-gel microextraction capillary an effective means for hyphenation of SPME and CME with liquid-phase separation techniques like HPLC [74,75] and CEC [39,51]. Since so l-gel technology has tunable selectivity, it offers the flexibility of incor porating sol-gel active organic ligand (polymer or monomer) with specific functional groups in the sol solution which can provide the selectivity to the created extracting sorbent toward target analytes. The extraction sorbents prepared using sol-gel appro ach are highly porous which gives them significantly high surface area and provides acce ptable sample capacity, and faster mass transfer even with thinner coatings [20]. So me of the sol-gel sorbents used in SPME and/or CME (Table 2.2) are desc ribed in following sections.

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72 Table 2.2 Summary of sol-gel sorbent used in SPME and/or CME. Name of sorbent Structure Ref. Hydroxy-terminated poly(dimethylsiloxane) (PDMS) HOSi O CH3 Si O CH3 CH3 Si OH CH3 CH3 CH3 n [20,41, 43] Hydroxy-terminated poly (dimethyldiphenylsiloxane) (PDMDPS) Si CH3 CH3 xSi y O O Si O H CH3CH3HO [44] Poly(vinyl alcohol) (PVA) [76] Polymethylphenylvinylsiloxane (PMPVS) Si CH3 SiO CH3 O Si O CH3CH3 CH=CH2 xy z [77] Divinyl benzene (DVB) CH2CH CH CH2 [78] Hydroxyfullerene (fullerol) C60OH n [79]

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73 5,11,17,23-tetratert -butyl25,27-diethoxy-26,28dihydroxycalix[4]arene [80] Amide bridged-calix[4]arene [81] Hydroxy-terminated dibenzo-14-crown-4 (OH-DB14C4) [82] Dihydroxy-terminated benzo15-crown-5 (DOH-B15C5) OO O O O HO(H2C)3OH2C HO(H2C)3OH2C [83]

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74 Alkoxy-terminated bisbenzo 16-crown-5 [84] (A) 4-allyldibenzo-18-crown-6 (B) 3-allylbenzo-15-crown-5 (C) allyloxyethoxymethyl-18crown-6 O O O O O O O O O O O O CH2CH CH2 O CH2CH CH2 O O O O O O CH2OCH2CH2OCH2CH CH2 A B C [85] (A) hydroxydibenzo-14-crown4 (OH-DB14C4) (B) dihydroxy-substituted saturated urushiol crown ether (DHSU14C4) (C) 3,5-dibutyl-unsymmetrydibenzo-14-crown-4-dihydroxy crown ether (DBUD14C4) O O O O OH OH -C15H31 n O O O O OH OH t-Bu t-Bu O O O O OH A B C [59,60 ]

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75 Heptakis (2,6-diO -methyl)cyclodextrin (DM-CD) O O H OCH3 OCH3 O 7 [86] -cyclodextrin ( -CD) [8789] Phenyl-terminated dendrimer with a triethoxysilyl root. [42] Poly-THF (H2C)4O n H HO [90]

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76 3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) H2C C CH3 C O O (CH2)3 Si OC H 3 OCH3 OCH3 [91] (A) Methyl acrylate (MA) (B) Methyl methacrylate (MMA) (C) Butyl methacrylate (BMA) H2C C H C O O CH3 (A) H2C C C H 3 C O O CH3 (B) H2C C C H 3 C O O C4H9 (C) [92] [A] (3,5’,3”-trisbenzyloxy-2’dodecyloxy[1,1’,4’,1”]terphenyl) [B] (2’,5’-bisbenzyloxy[1,1’,4’,1”]terphenyl) (A) O H HO OH R O HO OH (B) [93] Anilinemethyltriethoxysilane (AMTEOS) H N Si OC H 3 OCH3 OCH3 [94]

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77 2.5.1 Sol-gel PDMS and PDMDPS sorbents In these sorbents, solgel active hydroxyl terminat ed PDMS or PDMDPS polymers with surface methyl or phenyl groups ha ve served as sol-gel extraction media. Various precursors (alkoxides of Si, Ti, and Zr) have been successfully used for chemical immobilization of PDMS [20,41,43] and PDMDPS [44] on the surface of fused silica fiber (fiber-SPME) or inner surface of fuse d silica capillary (in-tube SPME or CME). Chong and co-workers [20] we re the first to use solgel approach to prepare SPME fibers. Hydroxy-terminated PDMS along with sol-gel precursor methyltrimethoxysilane (MTMOS) was reacted in presence of a sol-gel catalyst (trifluoroacetic acid contai ning 5% water) to produce a hybrid organic-inorganic polymeric network chemically bonded to the fu sed silica fiber surface. Due to the strong chemical bonding to the substrate, the hyb rid material provide d exceptionally high thermal and solvent stability. Moreover, the porous structure of the sol-gel coating facilitated efficient mass transfer of analyt es between the sorbent and aqueous media. This, in turn, facilitated faster extraction equilibrium compared to conventional thick PDMS coating which may take much longer ti me to reach the equilibrium. Due to the porous structure, a sol-gel hybrid organic-inor ganic material provides higher surface area. Consequently, a relativel y thin coating is sufficient to ac hieve an analyte detection limit equal to or even lower than that achieved using conventi onally coated sorbents. As indicated by the result obtained for BTEX analysis, an order of magnitude lower detection limit has been accomplished by the sol-gel PDMS coating, even though

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78 thickness was two-fifth of the c onventional PDMS coating [20]. Bigham and co-workers [41] demonstrated use of PDMS sol-gel coatings in CME (or in-tube SPME). They also demonstrated superior performance of sol-gel based PDMS coatings in direct extraction of organic analytes from aqueous media compared to conventional PDMS coatings. Later, Kim an d co-workers [43] de veloped a high pH resistant, surface bonded sol-gel titania-PDMS coating and demonstrated its application in CME coupled with HPLC for on-line extrac tion of PAHs, BETX and ketones. On the other hand, Alhooshani and co-workers [44] reported a sol-gel hybrid zirconia-PDMDPS coating for CME of PAHs, aldehydes ketones coupled with GC-FID. 2.5.2 Sol-gel PDMS-PVA sorbents Lopes and co-workers [76] prepared a co mposite sol-gel sorb ent using PDMS and poly (vinyl alcohol) (PVA) as organic moietie s. Polyvinyl alcohol was incorporated in the growing sol-gel network via polycondensat ion and acted as a strong cross-linking agent. The thermal stability of the composite phase was found to be superior compared to sol-gel PDMS sorbent. The improved ther mal stability of sol-gel PDMS-PVA was attributed to the additional cross-linking provided by the P VA in the reaction mixture. The enhanced thermal stability of SPME sorbents is extremely desirable because higher thermal stability of the sorbents can extend applicability of SPME toward higher-boiling compounds. Moreover, bleeding from the fiber coating during the thermal desorption (in GC injection port) is less likely to happen. Sol-gel PDMS-PVA showed better affinity

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79 towards polychlorinated biphe nyl (PCBs) compared with sol-gel PDMS coating [76]. Later experiments have also demonstrated the applicability of sol-gel PDMS-PVA sorbent for SPME of organochl orine pesticides and organop hosphorous pesticides [95]. 2.5.3 Sol-gel PDMS-PMPVS sorbents Yang and co-workers [77] have describe d preparation of sol-gel PDMS-PMPVS coated SPME fibers. Briefly, sol solution pr epared by mixing 40 mg of PMPVS, 90 mg of hydroxyl-terminated silicon oil (OH-TSO), 100 L of TEOS, 50 L of VTEOS, 10 mg of PMHS and 8 mg benzophenone, 400 L of methylene chloride and 120 L of TFA (5% water) was used to coat SPME fiber. Instead of using singl e precursor, TEOS, another precursor vinyltriethoxys ilane (VTEOS) was also used in conjunction with TEOS. Upon exposure to ultraviolet light, vinyl gr oups present in VTEOS and PMPVS reacted to form cross-links in presence of benzophe none (a free-radical initiator). Due to its inherent multifunctional composition and advant ages of sol-gel chemistry [19,20], sol-gel PDMS-PMPVS coatings showed superior efficiency for extraction of aromatic compounds (e.g., PAHs, BTEX etc.) compared commercial PDMS and PA coated SPME fibers. Sol-gel PMPVS coating was characte rized by good thermal st ability (350 C), long life time, and high extraction efficiency. Later same researchers [96,97] used same coating for analysis of organophosphorus pesticides.

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80 2.5.4 Sol-gel PDMS-DVB sorbents Liu and co-workers [78] developed a sol-gel based sorbent using OH-TSO and divinylbenzene (DVB) polymers for se lective extraction of phosphates and methylphosphonates from air and water samp les. Sol solution was prepared by thoroughly mixing 180 L of DVB, 60 mg of OH-TSO, 50 L of V TEOS, 10 mg of PMHS, 8 mg benzophenone, 100 L of methylen e chloride and 70 L trifluoroacetic acid (with 5% water, v/v). In order to prepare the coating, fused s ilica fibers were dipped into the sol solution and kept there for 30 min. When the coating was completed, the fibers were irradiated under ultrav iolet light for 30 min. Fina lly, the fiber was thermally conditioned up to 380 C under nitrogen flow. A comparison was made between sol-gel PDMS-DVB and commercial SPME coatings (PDMS, PA, and PDMS-DVB). Among all the phases compared, sol-gel PDMS-DVB coati ng showed the best extraction efficiency. Sol-gel PDMS-DVB coating was characteri zed by very high ther mal stability. After heating up to 380 C, no noticeable loss in extr action efficiency was observed. As a result of high thermal stability, it provided higher desorption temperature for analytes with high boiling points, and also elimin ated sample carryover still considered to be a common problem for commercial coatings. Same researchers [98] also synthesi zed hydroxy-terminated silicone oil-Bu methacrylate-divinylbenzene (OH-TSO-BMADVB) copolymer and prepared sol-gel OH-TSO-BMA-DVB coating for SPME. It s howed high extraction efficiency for both polar alcohols and fatty acids and nonpolar esters compared to commercial PDMS, PDMS-DVB and PA coated SPME fibers.

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81 2.5.5 Sol-gel PDMS-fullerene sorbents Fullerenes are closed-cage carbon molecules containing pentagonal and hexagonal rings. Because of their inherent properties like high hydrophobicity, high thermal stability, resistance to oxida tion, and the capability of strong ( and donoracceptor) interactions with va rious organic compounds have made it a very promising SPME sorbent [79]. Yu and co-workers [79] devel oped a sol-gel SPME coating using hydroxyfullerene (fullerol) with OH-TSO. So l-gel hydroxyfullerene coated SPME fibers were conditioned at as high as 360 C for 5 hours. The high thermal and solvent stability was attributed to the strong chemical bonding of the sorbent to the fused silica fiber, as well as the excellent thermal stability of the participating organic ingredients (fullerol). Also, the porous structure of the fullerene ba sed sol-gel coatings facilitated faster mass transfer between the sorbent and aqueous medi a, which aided establishment of extraction equilibrium significantly faster than commerc ial coatings. For example, polychlorinated biphenyls (PCBs) extracted on sol-gel PDMS -fullerol SPME coating required only 50 min to reach extraction equilibrium compared to a commercial PDMS coating which required several days to reach equilibrium [99]. Sol-gel PDMS-fullerol coatings were also used to aromatic amines. The results re vealed that sol-gel PDMS-fullerol coatings are not only suitable for non polar compounds but also very efficien t in extracting polar analytes.

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82 2.5.6 Sol-gel PDMS-calix{4}arene sorbents Calixarenes are cyclic oligomers prep ared from the reaction of phenols and aldehydes [100]. Since they possess a molecula r cavity of cylindrical architecture similar to that of cyclodextrins, they can form incl usion complexes. The unique characteristics of calixarenes such as small molecular size, good film forming propertie s, excellent thermal stability, and presence of func tional groups to interact with analytes have made them promising candidates for being used in SPME sorbents [80]. Zeng and co-workers [80] developed calix arene based sol-gel sorbents for SPME. These researchers synthesized 5,11,17,23tetra-tert-butyl25,27-diethoxy-26,28dihydroxycalix[4]arene and utili zed it as a new SPME sorben t. Sol-gel approach was followed to prepare a coating on a fused silica fiber using synthesized calix[4]arene as an organic components, OH-TSO as a sol-gel active polymer, 3-(2cyclooxypropoxyl)propyltrimethoxysila ne (KH-560) and TEOS as sol-gel precursors, poly(methylhydrosiloxane) (PMHS) as deactiv ating reagent, and trifluoroacetic acid (TFA) (with 5% water, v/v) as the solgel catalyst. OH-TSO was added along with calix[4]arene in the sol solution in order to increase the surface area of the coating. Several SPME fibers with different amount of calix[4]arene were prepared. All the solgel calix[4]arene coatings showed excelle nt thermal stability (380 C). Since calix[4]arene contains phenyl termination as well as a cavity in its structure, it is expected to exhibit high selectivity toward non polar aromatic compounds due to interaction, hydrophobic interactions and cavity-shaped cyclic molecular structure. Moreover, such coatings should efficiently extract polar aromatic amines through hydrogen bonding and

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83 dipole-dipole interactions. As was expected, calix[4]arene coatings demonstrated very high efficiency in extracting both non polar (BTEX, PAHs) and polar (aromatic amines) analytes. Later experiments, carried out using the same coating, demonstrated higher extraction efficiency than commercial PD MS-DVB and PA coated SPME fibers for extraction of chlorophenols [101]. They also utilized the same sol-gel calix[4]arene sorbent for the determination of phthalate acid esters plasticizers in polymeric materials [102]. Phthalic acid esters (PAE s) (the most commonly used additives in plastic) have been classified as priority pollutants by US Environmental Protection Agency (EPA) [103]. Therefore, a simple, low cost and rugge d method for determining PAEs in water is necessary. The sol-gel coated calix[4]arene SPME fibers were employed to determine the contents of phthalate ester-based plastici zers in blood bags, tran sfusion tubing, food packaging bag, and mineral water bottle. Relativ e affinity of PAEs were investigated by employing sol-gel calix[4]arene and three comme rcially available fibers (PDMS, PA, and PDMS/DVB). The results unequivocally dem onstrated the superiority of sol-gel calix[4]arene sorbent among all four phases tested. Zeng and co-workers [81] also utilized 25,27-dihydroxy-26,28-oxy (2 ,7 -dioxo3 ,6 -diazaoctyl)oxy-p-tert-butylcalix[4]arene (amide bridged calix[4]arene) to make solgel amide bridged calix[4]arene sorbent fo r headspace SPME of underivatized aliphatic amines from aqueous solution. The developed sol-gel amide bridged calix[4]arene SPME coatings showed all attributes of (e.g., high thermal stability (~ 380 C ), solvent stability, long life span, as well as highly porous surface morphology) previously re ported sol-gel

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84 calix[4]arene SPME coatings [80]. Owing to th e introduction of the polar amide bridge in calixarene molecules, the polarity of the co ating increased. As a consequence, these coatings exhibited better sensitivity to mo st of the investigated aliphatic amines compared to commercial polar coatings PDMS/DVB and PA. Recently, same researchers developed a novel SPME fiber coated with sol-gel (5,11,17,23-tetra-tert-butyl)-25,27-dihydroxy-26, 28-diglycidyloxycalix[4]arene/hydroxyterminated silicone oil (diglycidyloxy-C[4]/OH-TSO) and used it for determination of nine chlorobenzenes in soil ma trices [104]. Chlorobenzenes ar e used in larg e quantities as industrial solvents, pesticides, dielectric fl uids, deodorants and chemical intermediates. Due to their widespread use over several decades, chlorobenzenes have become very common in the environment. They are found in water, soil, sediments, and sewage sludge [105,106]. These compounds have high octanol –water partition coefficients [107], therefore biological accumulation can be expect ed in the aquatic ecosystem. Due to their acute toxicity [108] and the potential danger th ey pose to the environment [109], it is very important to monitor these compounds. The sol-gel diglycidyloxyC[4]/OH-TSO coated SPME fiber used for the extraction of ch lorobenzenes showed a better extraction capability than the coatings made with only OH-TSO. Also, comparison between sol-gel diglycidyloxy-C[4]/OH-TSO co ated SPME fiber with thos e of commercial PDMS and PDMS-DVB coated fibers showed that th e sol-gel diglycidyloxy-C[4]/OH-TSO coated fiber had the highest chlorobenzene extract ion efficiency among these fibers. The high extraction capability of the diglycidyloxyC[4]/OH-TSO fiber towards these compounds was attributed to the – interactions, the hydrophobic in teractions and some other

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85 specific interactions such as inclusion complexes in the cavities formed by the supramolecules. Using sol-gel diglycidyloxy -C[4]/OH-TSO coatings, detection limits were found at sub-ng/g in HS-SPME-GC-ECD experiments, which were about an order of magnitude lower than those given by the commercial PDMS coating for most of the compounds. 2.5.7 Sol-gel PDMS-crown ether sorbents Crown ethers are cyclic carbon compounds containing hetero atoms such as oxygen, nitrogen and sulfur. They are charac terized by a cavity structure, medium polarity and strong electronegati ve effect of hetero atoms on the crown ether ring. Table 3.3 (add figure of ref 31 in the table) lists most common crown ether based polysiloxane sorbents used in SPME. Zeng and coworkers [59] proposed a sol-gel based approach to coat SPME fibers with hydroxyl-terminated dibenzo-14-cr own-4 crown ethers (OH-DB14C4) and successfully utilized them in phenol analysis. Sol solution was prepared by mixing 8 mg of OH-DB14C4, 90 mg of OH-TSO, 10 mg of PMHS, 100 L of TEOS, 50 L of 3-(2Cyclooxypropoxyl)propyltrimethoxysilane (KH-560), and 100 L of me thylene chloride solvent. The so-gel reactions were cataly zed by adding 80 L of TFA (with 5% water, v/v). Due to the limited solubility of OHDB14C4, lower concentrations of OH-DB14C4 were used in sol-gel coating solution. Compar ison of distribution constants (K) of various phenols between aqueous phase and SPME coati ngs prepared with different amounts of

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86 OH-DB14C4 (0 mg, 4 mg, 8 mg) showed distri bution constants (K) va lues increased with the increase in the amount of added OHDB14C4. Sol-gel coated OH-TSO/OH-DB14C4 SPME fibers were characterized by high thermal stability. No apparent loss in extraction efficiency was observed even after being he ated at 350 C and also after 150 times repeated extractions. Same researchers also used previously reported [59] sol-ge l approach to make SPME coatings using dihydroxy-substituted satu rated urushiol crown ether (DHSU14C4) and dibutyl-unsymmetric-dibenzo-14-crown4-dihydroxy crown ether (DBUD14C4) [60] and investigated their selectivity toward ar omatic amines. Five different coatings (OHDB14C4/OH-TSO, DHSU14C4/OH-TSO, DBUD14C4/OH-TSO, OH-TSO, and OHDB14C4) were employed to compare the selec tivity of different crown ethers toward aromatic amines. The results suggested that OH-DB14C4/OH-TSO had the highest extraction efficiency. Among the three sol-gel crown ether coatings, extraction efficiency decreased with increasing num ber of alkyl groups (no al kyl group> n-C15H31> t-Bu) attached to the crown ether ring attributed to the decreased polarity of the coatings and increased steric hindrance. Among all the coatings teste d, sol-gel OH-DB14C4 (with no OH-TSO) had the lowest extraction efficiency indicating the presence of OH-TSO in the sol-gel structure helped the sorbent coating to spread uniformly onto the fused silica substrate. Although sol-gel OH-DB14C4/OH-TSO has been proved to be a superior coating, compared with commercial coatings it has relatively low polarity coating [110,111]. In addition, its low solubility in sol solution limits the concentration of OH-DB14C leading

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87 to low sample capacity [59]. In order to el iminate the inherent shortcoming of smaller crown ether, Wang and co-workers [83] synthesized dihydroxy-terminated benzo-15crown-5 (DOH-B15C5) possessing bigger ring si ze and higher polarity compared to that of smaller OH-DB14C4. Sol-gel SPME coatings were made using various amounts of DOH-B15C5 (0 mg, 10 mg, and 20 mg) along with 90 mg of OH-TSO, 10 mg of PMHS, 100 L of TEOS, 200 L of methylene and 80 L TFA (with 5% water, v/v). Evaluation of the thermal stability of these coatings showed that sol-gel co ating with no (0 mg) DOH-B15C5 added in the sol-gel coating solu tion cracked at 300 C. On the other hand, SPME coatings made with 10 mg and 20 mg of DOH-B15C5 in the sol-gel coating solution intact even after conditioned at 350 C. Also the selectivity study showed, compared to commercial SPME coatings (100 m PDMS and 85 m PA), sol-gel DOHB15C5 (67 m) SPME coating ha d highest efficiency for th e extraction of phenols. The excellent extraction efficiency of sol-gel DOH-B15C5 was attributed to enhanced surface area as well as sample capacity and hydrogen-bonding between the crown ether and phenolic compounds. Sol-gel DOH-B15C5/OH-TSO co ating has also been used for trace analysis of organochlorine pest icides (OCPs) in water [112]. Oganophosporuos pesticides (OPPs) have l ong been considered as a health and environmental hazard due to its toxicity and ubiquity in nature. C onsequently, there is always a great demand for an analytical method that is cheap, simple, fast, and highly sensitive that would ease the monitoring of tr ace levels of OPPs in water, food and other matrices. Yu and co-workers [84] s ynthesized allyloxy bisbenzo 16-crown-5 trimethoxysilane and used it as a precursor to prepare sol-gel bisbenzo crown ether/OH-

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88 TSO coating for SPME. Unlike other silicon oil based mixed sorbent systems where the loading of a organic moiety is limited by its low solubility and translates into poor to moderate impact on the selectivity of the co mposite sorbent, allyloxy bisbenzo 16-crown5 trimethoxysilane is highly soluble in sol so lution ingredient and can be added to OHTSO in a greater ratio. Sol solution contai ned 75 mg of allyloxy bisbenzo 16-crown-5 trimethoxysilane, 90 L of OH-TSO, 50 L TEOS, 10 L of PMHS, 300 L of methylene chloride and 80 L TFA (5% water). These sorbents dem onstrated very high thermal stability (350 C). Furthermore, no significant change in extraction sensitivity was observed from subsequent extractions of OPPs using sol-gel crown ether coating even after being washed with different solvents (e.g., nhexane, methylene chloride, acetone, and distilled water) for 1 hour. The extr aordinary thermal and solvent stability of the sol-gel crown ether coating was attributed to its strong chemical bonding to the fused silica fiber. Aliphatic amines are ubiquitous in nature due to their widespread use in industry as well as biodegradation pr oducts of organic compounds lik e proteins and amino acids or other nitrogenous compounds. Due to thei r toxicity and hazardous nature, lowmolecular-mass amines are considered to be important air pollutants. Moreover, secondary aliphatic amines are assumed to react with nitrile to form carcinogenic nitrosamines [113]. Therefore, analysis of a liphatic amines at trace levels in biological fluids, air, and water is of great interest. Ca i and co-workers [85] used sol-gel coatings made from three different crown ethers: 4-allyldiben zo-18-crown-6 (DB18C6), 3 allylbenzo-15-crow-5 (B15C 5), and allyloxyethoxymethyl -18-crown-6) (PSO18C6).

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89 They compared the performance of these solgel crown ether coatings with commercial PDMS and PA SPME coatings. The coating thicknesses of three sol-gel coatings DB18C6, B15C5, and PSO18C6 were 80-, 84-, a nd 82 m, respectively. The thicknesses of two commercial coatings, PDMS and PA, were 100 and 85 m, respectively. The extraction efficiencies of all five coatin gs were compared by extracting derivatized aliphatic amines under identic al conditions. The results indicated that sol-gel DB18C6 and B15C5 had higher extraction efficiencies than sol-gel PSO18C6. The presence of benzyl group in these crown ether was thought to be responsible for higher extraction of aliphatic amines by interactions with derivatized am ines. Particularly, the symmetric benzyl groups and greater number of oxygen atoms in the crown ether ring in sol-gel DB18C6 results in stronger interactions between the coating and the derivatized amines, and therefore, made this coating mo st efficient among all fi ve coatings employed in this investigation [85]. Moreover, the extraction efficiencies of two commercial coatings (PDMS and PA) were lower than the crown ether coatings, PDMS having the lowest. Enhanced surface area and sample capacity provided by sol-gel coating technology is one factor that helped achi eve this enhanced extraction sensitivity. Later same researchers used previously reported [85] sol-gel crown ethers for SPME of OPPs. They found sol-gel B15C5 co ating with higher pol arity had the best selectivity for OPPs [114].

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90 2.5.8 Sol-gel cyclodex trin sorbents Cyclodextrins (CDs) and their deri vatives have long been used as chromatographic stationary pha ses especially in chiral se parations [115] due to their unique properties, in particular presence of a chiral cavity, th e shape and size selectivity as well as its ability to form inclusion co mpounds with various analytes. Considering the positive attributes of cyclodextrins as chromatographic stationary phases, Fan and coworkers [87] developed a sol-ge l method for preparing sol-gel -CD coating for in-tube SPME coupled to HPLC for the determinati on of non-steroidal anti -inflammatory drugs in urine samples. In order to prepare th e sol solution, 0.1 mL TEOS was added to 0.1 mL 0.01 M HCl and stirred at 60 C until became homogeneous. Another solution was made using 0.05 g 3-glycidoxypropyltrimet hoxysilane (KH-560) derivatized -CD dissolved in 0.3 mL acetonitrile and 0.5 mL 0.01M HCl. Both solutions were mixed thoroughly and centrifuged. The resulting sol solution was used to coat the inner surface of capillary. After desired coating thickness was achieved the capillary was aged for 48 hours. Later, a 60 cm piece of sol-gel cyclodextrin coated ca pillary was used for in-tube SPME of urine samples. Hu and co-workers [88,89] showed use of poly(dimethylsiloxane)/ cyclodextrin (PDMS/ -CD) coating membrane for SPME of PAHs, amines and phenols. Recently, Zhou and co-workers repor ted [86] fiber coated with -cyclodextrin derivatives. The sol solution contained 30 mg of Heptakis (2,6-di-O-methyl)cyclodextrin (DM-CD) 150 l of methylene chloride 90 mg of OH-TSO, 100 of TEOS, 50 l KH-560, 10 mg of PMHS and 100 l TF A (with 5% water,v/v). The coating thickness of DM-CD/OH-TSO fiber was 65 m. DM-CD/OH-TSO coated fibers

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91 were used for HS-SPME of ephedrine (EP) and methamphetamine (MP) in human urine. Detection limits of 0.33 ng/ml for EP and 0.60 ng/ml for MP were achieved in HSSPME-GC experiments. 2.5.9 Sol-gel dendrimer sorbent Dendrimers [116,117] are highly branched m acromolecules create d in a step-wise fashion using simple branched monomeric un its, the nature and functionality of which can be easily controlled and varied. They possess open and vacuous structures characterized by channels and pockets which are especially true for higher generations [118]. Because of their tree-l ike branched architecture, functionalized dendrons are ideal candidates for sorbents to be used in anal ytical sample enrichment and separations. Dendrimers have been used as: (a) pseu do-stationary phases in electrokinetic chromatography [119,120], (b) bonded stationary phases in capillary electrochromatography [121], (c) chiral sta tionary phases in HPLC [122], and (d) GC stationary phases [123]. Kabir and co-worke rs [42] introduced sol-gel dendrimers as sorbent in CME for solvent-free microextra ction of both polar and nonpolar analytes from aqueous samples. The sol solution contained 5 L of MTMOS, 50 mg of phenylterminated dendrimer with a triethoxysilyl containing root, 10 L of HMDS, 25 L of PMHS, and 50 L of TFA in 900 L of dichloromethane solven t. After filling, the sol solution was kept inside the capillary for 30 min to facilitate the formation of a surfacebonded sol–gel dendrimer coating. The fr ee unbonded portion of the sol solution was

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92 later expelled from the capillary under helium pressure (50 psi) and the coated capillary was purged with helium for an hour. The coating thickness was estimated at 0.5 m. Detection limits on the order of ng/L were ach ieved for the extracti on of both polar and nonpolar analytes including PAHs, aldehydes, ketones, phenols, and alcohols in CME– GC–FID experiments using so l–gel dendrimer-coated micr oextraction capillaries. 2.5.10 Sol-gel poly-THF sorbent Poly-THF (also called polytetramethylen e oxide, PTMO) is a hydroxy-terminated polar material that has been used as an organic component to synthesize organic– inorganic hybrid materials [124-126]. Sol–gel poly-THF has been used as bioactive bone repairing material [127], and as a proton c onducting solid polymer el ectrolyte that might allow the operation of high te mperature fuel cells [128]. Kabir and co-workers [90] first describe d a sol-gel chemistry-based approach for in situ creation poly-THF based hybrid orga nic-inorganic CME coatings on the inner walls of fused silica capillaries. The sol-ge l coating was created on the inner walls of a fused silica capillary using a sol solution containing polyTHF (250 mg) as an organic component, MTMOS (20 L) as a sol-gel precursor, TFA (100 L) (with 5% water, v/v) as a sol–gel catalyst, and HMDS (20 L) as a deactivating reagent. In CME-GC-FID experiments, pictogram/liter (pg/L) level de tection limits were reported for the analytes of different polarity including PAHs, aldehyd es, ketones, chlorophenols, and alcohols extracted from aqueous samples using so l–gel poly-THF coated microextraction

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93 capillaries. 2.5.11 Miscellaneous sol-gel sorbents In addition to the aforementioned sorbents miscellaneous sol-gel chemistry-based sorbents have been reported in the literature. Liu and co-workers [129] used 3 -(Trimethoxysilyl)propyl methacrylate (TMSPMA) to prepare the sol-gel-derive d TMSPMA-hydroxyl-terminated silicone oil (TMSPMA-OH-TSO) extracting sorbent for HS-SPME of aroma compounds in beer. TMSPMA, which contains both methacrylat e and alkoxysilane groups, served as a bifuntional reagent. Sol-gel TMSPMA-OH-TSO (a medium polarity coating) was very effective in carrying out simultaneous extractio n of both polar (alcoho ls, fatty acids) and nonpolar (esters) analytes in beer. The extr action temperature, extraction time, and ionic strength of the sample matrix were modi fied to allow for maximum sorption of the analytes onto the sol-gel TMSPMA-OH-TSO coat ed fiber. The extraction efficiency of sol–gel-derived TMSPMA-OHTSO fiber was found to be much better than PDMS, PDMS-DVB and PA coated commercial SPME fi bers. They also [92] described three types of novel acrylate/silicone co-pol ymer coatings: (1) co-poly(methyl acrylate/hydroxy-terminated silicone oil) (MA/OH-TS O), (2) co-poly(methyl methacrylate/OH-TSO) (MMA/OH-TSO), and (3) co-poly(butyl methacrylate/OH-TSO) (BMA/OH-TSO) prepared using sol-gel tech nology and subsequently applied to HSSPME of 2-chloroethyl ethyl sulfide (CEES), a surrogate of mustard, in soil. Among the

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94 three kinds of acrylate/silicone coated SPME fibers, the sol-ge l-derived BMA/OH-TSO coating had the highest affinity for CEES. Sol-gel-derived BMA/OHTSO coatings were also used for HS-SPME of medium and long chain fatty acids after derivatization and applied to the analysis of fatty acids in lung tissues by coupling to GC–MS [130]. The experimental parameters for derivatization, HS-SPME, and desorption were optimized. Fatty acids in cancerous lung tissu es from five patients with lung cancer were determined under the optimized conditions. Normal lung tissues from the same five patients were used as controls. The sol-gel BMA/OHTSO coatings showed higher extraction efficiency for fatty acids afte r derivatization when compared with commercial PDMS and PDMS/DVB coated fibers. The higher extractio n efficiency was attributed to the threedimensional network in the sol-gel BMA/OHTSO coating. Later same researchers [131] presented a novel alumina-base d hybrid organic-inorganic sol-gel coating for SPME. Compared to the sol-gel silic a-based coating, the alumina-based coating demonstrated excellent pH stability. In addition, devel oped coatings possessed good thermal stability and coating preparation reproduc ibility. Practical applicabilit y of the prepared aluminaOH-TSO fiber was demonstrated through the anal ysis of volatile alc ohols and fatty acids in beer. Basheer and co-workers [93] synthesized hydrophilic (3,5’,3” -trisbenzyloxy-2’dodecyloxy-[1,1’,4’,1”]terphenyl) and am phiphilic (2’,5’-bisbenzyloxy[1,1’,4’,1”]terphenyl) oligomers and coated them on fused silica fibers using a sol-gel technique. The extraction efficiency of th e sol–gel coatings was evaluated for the extraction of both non-polar and polar analyt es, including organoc hlorine pesticides,

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95 triazine herbicides, estrogens and alkyl phe nols (APs) and bisphenol-A (BPA). Compared with commercially available SPME sorbents such as PDMS-DVB and PA, the new materials showed comparable selectivity and sensitivity towards both non-polar and polar analytes. The new coatings gave good linear ity and detection limits For example with triazines, a detection lim it of < 0.005 g/L, precision from 5.0 to 11.0% (n = 6) and linearity of the calib ration plots (0.5 to 50 g/L) were obtained. Hu and co-workers [132] reported sol–gel derived anilinemethyltriethoxysilanepolydimethylsiloxane (AMTEOS/PDMS) sorbents for SPME. The sol-gel AMTEOS/PDMS coating was designed to aim at – interaction between the aromatic compounds and the phenyl group in the sol–ge l network. The novel SPME fiber showed high extraction efficiency, good thermal stab ility and long lifetime compared with commercial SPME coating (PDMS) for th e extraction of monocyclic aromatic hydrocarbons (MAHs) and PAHs. LODs were between for MAHs 0.6 3.8 g/L and 0.2 1.5 g/L for PAHs.

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96 2.6 References to chapter 2 [1] C. Brinker, G. Scherer, Sol–Gel Scie nce. The Physics and Chemistry of Sol–Gel Processing, Academic Press, San Diego, CA, 1990. [2] M. Ebelmen, Ann. Chim. Phys. 15 (1845) 319. [3] M. Ebelmen, Ann. Chim. Phys. 16 (1846) 129. [4] M. Ebelmen, Comptes. Rend. de l'Acd des Sciences 25 (1847) 854. [5] D.I. Mendeleyev, Khim. Zhur. Sok. i. Eng. 4 (1860) 65. [6] C.B. Hurd, Chem. Rev. 22 (1938) 403. [7] W. Geffcken, E. Berger, in, German Patent, 1939. [8] R. Roy, J. Am. Ceram. Soc. 39 (1956) 145. [9] R. Roy, J. Am. Ceram. Soc. 52 (1969) 344. [10] W. Stober, A. Fink, E. Bohn, J. Colloid. Interface. Sci. 26 (1968) 62. [11] H. Dislich, Angew Chem. 10 (1971) 363. [12] L. Levene, I.M. Thomas, in, U.S. Patent 3,640,093, 1972. [13] J.D. Mackenzie, J. Sol-Gel. Sci. Technol. 26 (2003) 23. [14] H. Schmidt, J. Non-Cryst. Solids 73 (1985) 681. [15] H. Schmidt, Mater. Res. Soc. Symp. Proc. 32 (1984) 327. [16] H.J. Cortes, C.D. Pfeiffer, B.E. Ri chter, T.S. Stevens, J. High Resolut. Chromatogr. Chromatogr Commun. 10 (1987) 446. [17] A.L. Crego, J.C. Diez-Masa, M. V. Dabrio, Anal. Chem. 65 (1993) 1615. [18] Y. Guo, L.A. Colon, Anal. Chem. 67 (1995) 2511. [19] D. Wang, S.L. Chong, A. Ma lik, Anal. Chem. 69 (1997) 4566.

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97 [20] S.L. Chong, D. Wang, J.D. Hayes, B.W. Wilhite, A. Malik, Anal. Chem. 69 (1997) 3889. [21] H. Minakuchi, K. Nakanishi, N. Soga, N. Ishizuka, N. Tanaka, J. Chromatogr. A 762 (1997) 135. [22] N. Ishizuka, H. Minakuchi, K. Nakanish i, N. Soga, H. Nagayama, K. Hosoya, N. Tanaka, Anal. Chem. 72 (2000) 1275. [23] N. Tanaka, H. Kobayashi, K. Nakanish i, H. Minakuchi, N. Ishizuka, Anal. Chem. 73 (2001) 420A. [24] M.I. Sarwa, Z. Ahmad, Eur. Polym. J. 36 (2000) 89. [25] C. Tilgner, P. Fischer, F.M. Bohnen, H. Rehage, W.F. Maier, Microporous Mater. 5 (1995) 77. [26] S.S. Kistler, J. Physical Chem. 36 (1932) 52. [27] H. Schmid, A. Kaiser, M. Rudolph, A. Lentz, Science of Ceramic Chemical Processing, Wiley, NY, 1986, p.87. [28] T. Ogoshi, Y. Chujo, Compos. Interfaces 11 (2005) 539. [29] S. Sakka, K. Kamiya, in Proc. Ing. Sy mp. Factors Densification Sintering Oxide Non-Oxide Ceram, Gakujutsu Bunk en Fukyu-kai, Tokyo, Japan, 1979, p. 101. [30] P.B. Dorain, J.J. Rafalko, J.E. Feeney, C.E. Forbes, R.V. Carney, T.M. Che, in Materials Research Society Symposium, MA, USA, 1988, p. 523. [31] W. Jost, H.E. Hauck, in F.Z.S.G. Shuomingshu (Editor), CHINA, 1987, p. 17. [32] M.T. Harris, R.R. Brunson, C.H. By ers, J. Non-Cryst. Solids 121 (1990) 397. [33] T. Yamamoto, M. Mori, T. Maeda, in J.K.T. Koho (Editor), Nakato Kenkyusho K. K., Japan; Osaka Gas Co., Ltd., 1988, p. 5. [34] I.C. Tilgner, P. Fischer, F.M. Bohnen, H. Rehage, W.F. Maier, Microporous Mater. 5 (1995) 77. [35] R.J.P. Corriu, D. Leclercq, Angew. Chem. Int. Ed. Engl. 35 (1996) 1420. [36] A.M. Buckley, M. Greenblatt, J. Chem. Ed. 71 (1994) 599.

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98 [37] H. Minakuchi, K. Nakanishi, N. Soga N. Ishizuka, N. Tanaka, Anal. Chem. 68 (1996) 3498. [38] H. Kobayashi, C. Smith, K. Hosoya, T. Ikegami, N. Tanaka, Anal. Sci. 18 (2002) 89. [39] W. Li, D. Fries, A. Ali, A. Malik, Anal. Chem. 76 (2004) 218. [40] J.D. Hayes, A. Malik, Anal. Chem. 72 (2000) 4090. [41] S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Ali, A. Malik, Anal. Chem. 74 (2002) 752. [42] A. Kabir, C. Hamlet, K.S. Yoo, G.R. Newkome, A. Malik, J. Chromatogr. A 1034 (2004) 1. [43] T.Y. Kim, K. Alhooshani, A. Kabir, D.P. Fries, A. Mali k, J. Chromatogr. A 1047 (2004) 165. [44] K. Alhooshani, T.-Y. Kim, A. Kabir, A. Malik, J. Chromatogr. A 1062 (2005) 1. [45] S. Kulkarni, L. Fang, K. Alhooshani A. Malik, J. Chro matogr. A 1124 (2006) 205–216. [46] J.V. Hinshaw, LC-GC Europe (2003) 2. [47] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [48] L. Cai, J. Xing, L. Dong, C. Wu, J. Chromatogr. A 1015 (2003) 11. [49] L. Yun, Anal. Chim. Acta 486 (2003) 63. [50] J.D. Hayes, A. Malik, Anal. Chem. 73 (2001) 987. [51] J.D. Hayes, A. Malik, J. Chromatogr. B 695 (1997) 3. [52] A. Fidalgo, L.M. Ilharco, J. Non-Cryst. Solids 283 (2001) 144. [53] J.D. Brennan, J.S. Hartman, E.I. Ilni cki, M. Rakic, Chem. Mater. 11 (1999) 1853. [54] S.A. Rodrigues, L.A. Colon, Chem. Mater. 11 (1999) 754. [55] M. Pursch, A. Jaeger, T. Schneller, R. Brindle, K. Albert, E. Lindner, Chem. Mater. 8 (1996) 1245.

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99 [56] S.A. Jones, S. Wong, J.M. Burlitch S. Viswanathan, D.L. Kohlstedt, Chem. Mater. 9 (1997) 2567. [57] J. Gnado, P. Dhamelincourt, C. Pelegris, M. Traisnel, A.L.M. Mayot, J. NonCryst. Solids 208 (1996) 247. [58] R.M. Almeida, C.G. Pantano, J. Appl. Phys. 68 (1990) 4225. [59] Z. Zeng, W. Qiu, Z. Hu ang, Anal. Chem. 73 (2001) 2429. [60] Z. Zeng, W. Qiu, M. Yang, X. Wei, Z. Huang, F. Li, J. Chromatogr. A 934 (2001) 51. [61] S.A. Rodriguez, L.A. Colon, Appl. Spectrosc. 55 (2001) 472. [62] M.T. Dulay, J.P. Quirino, B.D. Bennett, M. Kato, R.N. Zare, Anal. Chem. 73 (2001) 3921. [63] M. Kato, K. Sakai-Kato, T. Toyo'oka, M.T. Dulay, J.P. Quirino, R.N. Zare, J. Chromatogr. A 961 (2002) 45. [64] A. Kasgz, K. Yoshimura, T. Misono, Y. Abe, J. Sol–Gel Sci. Technol. 1 (1994) 185. [65] C.J.T. Landdry, B.K. Cltrain, J.A. We sson, N. Zumbulyadis, Polymer 33 (1992) 1496. [66] Y. Fu, Q.-Q. Ni, M. Iwamoto, J. Non-Cryst. Solids 351 (2005) 760. [67] Z. Dang, B.G. Anderson, Y. Amenomiya, B.A. Morrow, J. Phys. Chem. 99 (1995) 14437. [68] C. Guermeur, J. Lambard, J.F. Gerard, C. Sanchez, J. Mater. Chem. 9 (1999) 769. [69] D.C.M. Dutoit, M. Shneider, A. Baiker, J. Catal. 153 (1995) 165. [70] J.M. Fraile, J.I. Garcia, J.A. Ma yoral, E. Vispe, J. Catal. 233 (2005) 90. [71] C.A. Muller, M. Maciejewski, T. Ma llat, A. Baiker, J. Catal. 184 (1999) 280. [72] M.S.M. Saifullah, D.J. Kang, K.R.V. Subramanian, M.E. Welland, K. Yamazaki, K. Kurihara, J. Sol–Gel Sci. Technol. 29 (2004) 5.

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100 [73] M.R. Boccuti, K.M. Rao, A. Zecchina, G. Leofanti, G. Petrini, Stud. Surf. Sci. Catal. 48 (1989) 133. [74] J.J. Kirkland, J.W. Henderson, J.J. De Stefano, M.A.v. Straten, H.A. Claessens, J. Chromatogr. A 762 (1997) 97. [75] T.P. Gbatu, K.L. Sutton, J.A. Caruso, Anal. Chim. Acta 402 (1999) 67. [76] A.L. Lopes, F. Augusto, J. Chromatogr. A 1056 (2004) 13. [77] M. Yang, Z.R. Zeng, W.L. Qiu, Y. L. Wang, Chromatographia 56 (2002) 73. [78] M.M. Liu, Z.R. Zeng, C.L. Wang, Y.J. Tan, H. Liu, Chromatographia 58 (2003) 597. [79] J. Yu, L. Dong, C. Wu, L. Wu, J. Xing, J. Chromatogr. A 978 (2002) 37. [80] X. Li, Z. Zeng, S. Gao, H. Li, J. Chromatogr. A 1023 (2004) 15. [81] X. Li, Z. Zeng, J. Zhou, S. Gong, W. Wang, Y. Chen, J. Chromatogr. A 1041 (2004) 1. [82] Z. Zeng, W. Qiu, Z. Hu ang, Anal. Chem. 73 (2001) 2429. [83] D. Wang, J. Xing, J. Peng, C. Wu, J. Chromatogr. A 1005 (2003) 1. [84] J. Yu, C. Wu, J. Xing, J. Chromatogr. A 1036 (2004) 101. [85] L. Cai, Y. Zhao, S. Gong, L. D ong, C. Wu, Chromatographia 58 (2003) 615. [86] J. Zhou, Z. Zeng, Anal. Chim. Acta. 556 (2006) 400 – 406. [87] Y. Fan, Y.Q. Feng, S.L. Da, Z.H. Wang, Talanta 65 (2005) 111. [88] Y.-l. Fu, Y.-l. Hu, Y.-j. Zheng, G.-K. Li, J. Sep. Sci. 29 (2006) 2684. [89] Y. Hu, Y. Yang, J. Huang, G. Li, Anal. Chim. Acta. 543 (2005) 17. [90] A. Kabir, C. Hamlet, A. Malik, J. Chromatogr. A 1047 (2004) 1. [91] M. Liu, Z. Zeng, B. Xiong, J. Chromatogr. A 1065 (2005) 287–299. [92] M. Liu, Z. Zeng, H. Fang, J. Chromatogr. A 1076 (2005) 16.

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101 [93] C. Basheer, S. Jegadesan, S. Valiyav eettil, H.K. Lee, J. Chromatogr. A 1087 (2005) 252. [94] Y.-l. Hu, Y.-l. Fu, G.-K. Li Anal. Chim. Acta 567 (2006) 211–217. [95] V.G. Zuin, A.L. Lopes, J.H. Yariwa ke, F. Augusto, J. Chromatogr. A 1056 (2004) 21. [96] Y. Wang, Z. Zeng, M. Yang, C. Don g, Wuhan Daxue Xuebao, Lixueban 52 (2006) 137. [97] Y. Wang, Z. Zeng, M. Yang, C. Do ng, X. Wang, Wuhan Ligong Daxue Xuebao 27 (2005) 37. [98] M. Liu, Z. Zeng, Y. Tian, Anal. Chim. Acta 540 (2005) 341. [99] M. Llompart, K. Li, M. Fingas, Anal. Chem. 70 (1998) 2510. [100] C.D. Gutsche, Calixarenes, Roya l Society of Chemistry, Cambridge, 1989. [101] X. Li, Z. Zeng, J. Zhou, Anal. Chim. Acta. 509 (2004) 27. [102] X. Li, Z. Zeng, Y. Chen, Y. Xu, Talanta 63 (2004) 1013. [103] A. Penalver, E. Pocurull, F. Borrull, R.M. Marce, J. Chromatogr. A 872 (2000) 191. [104] X. Li, Z. Zeng, Y. Xu, Anal Bioanal. Chem. 384 (2006) 1428. [105] M.N. Sarrion, F.J. Santos, M.T. Ga lceran, J. Chromatogr. A 819 (1998) 197. [106] F.J. Santos, M.N. Sarrion, M.T. Galceran, J. Chroma togr. A 771 (1997) 181. [107] B.G. Oliver, K.D. Bothen, Anal. Chem. 52 (1980) 2066. [108] A. Belfroid, W. Seinen, K. Vangest el, J. Hermens, Chemosphere 26 (1993) 2265. [109] Y. Wang, H.K. Lee, J. Chromatogr. A 803 (1998) 291. [110] C.Y. Wu, L.S. Cai, Y.J. Wang, H. M. Han, Z.R. Zeng, Z.Y. Yu, H. Yuan, Chromatographia 37 (1993) 374. [111] J.L. Ge, R.N. Fu, Z.F. Huang, Y. T. Wang, J. Microcol. Sep. 3 (1991) 250.

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102 [112] D. Wang, J. Peng, C. Xing, Y. Wu, J. Xu, J. Chromatogr. Sci. 58 (2003) 57. [113] G. Audunsson, Anal. Chem. 60 (1988) 1340. [114] L. Cai, S. Gong, M. Chen, C. Wu, Anal. Chim. Acta. 559 (2006) 89. [115] T. Cserhati, E. Forgacs, Cyclodextri ns in Chromatography, Royal Society of Chemistry, Cambridge, UK, 2003. [116] G.R. Newkome, Z. Yao, G.R. Baker, V.K. Gupta, J. Org. Chem. 50 (1985) 2003. [117] D.A. Tomalia, H. Baker, J. Dewald, M. Hall, G. Kallos, S. Martin, J. Roeck, J. Ryder, P. Smith, Polym. J. 17 (1985) 117. [118] G.R. Newkome, C.N. Moorefield, F. Vogtle, Dendrimers and Dendron. Concept, Synthesis, Applications, Wiley-VCH, Weinheim, 2001. [119] S.A. Kuzdzal, C.A. Monnig, G.R. Newkome, C.N. Moorefield, J. Chem. Soc., Chem. Commun. 18 (1994) 2139. [120] C.P. Palmer, N. Tanaka, J. Chromatogr. A 792 (1997) 105. [121] H.C. Chao, J.E. Hanson, J. Sep. Sci. 25 (2002) 345. [122] B.T. Mathews, A.E. Beezer, M.J. Snowden, M.J. Hardy, J.C. Mitchell, Chromatographia 53 (2001) 147. [123] G.R. Newkome, K.S. Yoo, A. Kabir, A. Malik, Tetrahedron Lett. 42 (2001) 7537. [124] H. Goda, C.W. Frank, Chem. Mater. 13 (2001) 2783. [125] C.S. Betrabet, G.L. Wilkes, Chem. Mater. 7 (1995) 535. [126] T. Higuchi, K. Kurumada, S. Naga mine, A.W. Lothongkum, M. Tanigaki, J. Mater. Sci. 35 (2000) 3237. [127] M. Kamitakahara, M. Kawashita, N. Miyata, T. Kokubo, T. Nakamura, Biomaterials 24 (2003) 1357. [128] I. Honma, O. Nishikawa, T. Sugimo to, S. Nomura, H. Nakajima, Fuel Cells 2 (2002) 52. [129] M. Liu, Z. Zeng, B. Xiong, J. Chromatogr. A 1065 (2005) 287.

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103 [130] D. Cha, M. Liu, Z. Zeng, D.e. Cheng, G. Zhan, Anal. Chim. Acta. 572 (2006) 47. [131] M. Liu, Y. Liu, Z. Zeng, T. Peng, J. Chromatogr. A 1108 (2006) 149. [132] Y.-l. Hu, Y.-l. Fu, G.-K. Li Anal. Chim. Acta. 567 (2006) 211.

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104 CHAPTER 3 SOL-GEL IMMOBILIZE D CYANO-POLYDIMETHYL SILOXANE COATING FOR CAPILLARY MICROEXTRACTION 3.1 Introduction Solid-Phase microextraction (SPME) [1] of polar analytes such as carboxylic acids, alcohols, amines, phenols, etc. from an aqueous medium often poses difficulty due to their high affinity toward water. For effici ent extraction of such analytes from aqueous samples the SPME coating must have polarity high enough to compete with water for the analyte molecules. However, polar coatings are difficult to immobilize on a silica substrates using conventional techniques [2]. The absence of chemical bonds between the SPME coating and fused silica fiber is consider ed to be responsible for low thermal and solvent stability of conventionally prepared SPM E coatings [3]. If such coatings are used for the extraction of polar analytes from aqueous media, desorption step becomes problematic and often leads to undesired e ffects such as incomplete desorption and sample carryover. Sol-gel coatings [3,4] were developed to provide an effective solution to these problems that inherently arises from the us e of in conventional SPME coatings. The solgel coatings offer several advantages. First, sol-gel coatings are chemically anchored to

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105 the fused silica substrate. The presence of ch emical bonds ensures thermal stability of the coatings, and thereby facilitates application of higher temperatures for effective desorption of high-boiling analytes. Thanks to these chemical bonds, so l-gel coatings also possess high solvent stability [4]. Second, th e sol-gel coatings usually have a porous structure enhancing the surface area of the extracting phase. This enhanced surface area allows the use of thinner coatings to achieve faster extraction and desired level of sample capacity [3]. Third, the selectivity of a sol-gel coating can be easily fine tuned by changing the composition of the used sol solution. Both conventional and sol-gel coatings have been used to extract polar compounds (e.g., free carboxylic ac ids, alcohols, etc.) from aqueous media. Pan and coworkers [5] have demonstrated the possibility of achieving improved limits of detection for short-chain (C2–C10) fatty acids via headspace extrac tion and in-fiber derivatization on poly(acrylate) (PA) coated SPME fibe r. Mixed phase coatings such as carbowax/divinylbenzene (CW/ DVB) [6-8], polydimethylsiloxane/divinylbenzene (PDMS/DVB) [8,9], polydimethylsiloxa ne/Carboxen (PDMS/Carboxen) [8,10], polydimethylsiloxane/Carboxen/divinylbenzen e (PDMS/CAR/DVB) [8] have been used for the extraction of highly polar compound s. The use of 3-(trimethoxysilyl)propyl methacrylate-hydroxyl-terminated silicone oil (TMSPMA-OH-TSO) [11] and hydroxyterminated silicone oil-butyl methacryl ate-divinylbenzene ( OH-TSO-BMA-DVB) [12] copolymer to prepare sol-gel coatings have also been reported for the extraction of alcohols and fatty acids in conjunction wi th temperature and sample matrix pH adjustments. In all these reports manipula tion to the operational conditions (e.g., sample

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106 derivatization, temperatur e control, and pH of sample ma trix, etc.) was used to improve the extraction efficiency. This however, increases the numbe r of steps involved in the extraction process with a concomitant increase in the extraction time as well as the error associated with it. It is, therefore, highl y desirable to develop coatings capable of providing efficient extraction of polar compoun ds without requiring such adjustments in operating conditions. Chromatographic stationary phases cont aining cyano functional group [13] are known to be extremely polar, and may prove to be highly effective in the microextraction of polar analytes from aqueous samples. Cyanopropylpolysiloxane s exhibit both polar and polarizable characteristics and are among the most useful stationary phases with respect to polarity at both low and high te mperatures. The cyano group, attached to the siloxane backbone via a three-methylene (-CH2) spacer, is dipolar and strongly electron attracting, hence displaying dipole-dipole, di pole-induced dipole, and charge-transfer interactions. The unshared electron pair on th e nitrile nitrogen may form intermolecular hydrogen-bonds with suitable hydrogen-donor molecules in the sample such as phenols. These characteristics of cyano stationary phases are responsible for increased affinity of these phases for alcohols, ketones, esters, and analytes bearing -electrons. Cyano stationary phases have been used in GC [14-18], HPLC [19-21], capillary electrochromatography (CEC) [22] and as an extraction medium in solid-phase extraction (SPE) [23-25]. Although cyanopropylpolysiloxane s might be useful for extracting highly polar compounds, conventionally prepared cyano coatings (h aving no chemical bond to the substrate) are not stable at elevated temperatures [26,27] The sol-gel approach solves

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107 this problem by chemically anchoring such polar coatings onto the fu sed silica surface. A recent publication from our group [28] describes sol-gel cyanopropyl-based coatings for capillary microextraction (C ME, also called in-tube SPME). In this dissertation, we provide a detail account on in situ creation of sol-gel coatings containing cyanopropyl and poly(dimethylsiloxane) compon ents (sol-gel CN-PDMS coatings), and explain how sol-gel chemistry can provide an effective means to immobilize such coatings on the inner walls of fused silica capillaries for use in CME. We also demonstrate the effectiveness of sol-gel CN-PDMS coatings in the simultaneous extraction of highly polar, moderately polar, and nonpolar analytes fr om aqueous sample matrices – an analytical task that is difficult to accomplish using conventional SPME coatings. 3.2 Experimental section 3.2.1 Equipment All the CME-GC experiments with sol-gel CN-PDMS coated capillaries were performed on a Shimadzu Model 17A GC (Shimadzu, Kyoto, Japan) equipped with a flame ionization detector (FID) and a splitsplitless injector. A Barnstead Model 04741 Nanopure deionized water system (Barnst ead/Thermolyne, Dubuque, IA) was used to obtain ~16.9 M water. A homebuilt, gas pressure-operated capillary filling/purging device [29] was used to rinse the fused sili ca capillary with solvents, fill it with sol

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108 solution, expel the sol solution from the capillary at the end of sol-gel coating process, and purge the capillary with helium (F igure 2.4). A vortex shaker model G-560 (Scientific Industries, Bohemia, NY) was used to mix sol-gel ingredients. A ThermoIEC model Micromax microcentrifuge (Needham Heights, MA) was used to separate the sol solution from the precipitate (if any) at 14 000 rpm (~ 15 915 g). A JEOL model JSM-35 scanning electron microscope (SEM) was used to investigate the surface morphology of sol-gel CN-PDMS coated capillaries. An inhouse designed liquid sa mple dispenser [30] was used to perform CME via gravity-fed fl ow of the aqueous samples through the solgel CN-PDMS coated capillar y (Figure 3.1). 3.2.2 Materials and chemicals Fused silica capillary (250 m i.d.) w ith a protective polyimide coating on the external surface was obtained from Polymi cro Technologies (Phoenix, AZ). HPLC-grade solvents (dichloromethane, methanol, and tetrahydrofuran (THF)), Kimwipes, polypropylene microcentrifuge tubes (2.0 mL), and 7.0 mL borosilicate vials (used to store standard solutions) were purchased from Fisher Scientific (Pittsburgh, PA). Polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, fluorene, phenanthrene, fluoranthene), aldehydes (nonanal, 4-isopropy lbenzaldehyde, 4-tert-butylbenzaldehyde, dodecanal), ketones (butyrophenone, valerophenone, hexanophenone, benzophenone, anthraquinone), aniline derivatives ( N,N -dimethylaniline, N -butylaniline, acridine, benzanilide), substituted phenols (2,4 -dichlorophenol, 2,4,6-trichlorophenol,

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109 Figure 3.1 Gravity-fed sample delivery system fo r capillary microextraction. Adapted from ref. [30] with permission.

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110 4-chloro-3-methylphenol, pentachlorophenol), fatty acids (hexanoic acid, nonanoic acid, decanoic acid, undecanoic acid), tetr aethoxysilane (TEOS, 99%), 1,1,1,3,3,3hexamethyldisilazane (HMDS, 99.9%), and trifluoroacetic acid (TFA, 99%) were purchased from Aldrich (Milwaukee, WI). Alcohols (1-heptanol, 1-octanol, 1-nonanol, and 1-decanol) were purchased from Acros (Pittsburgh, PA). Silanol terminated PDMS was obtained from United Chemical Technologies (Bristol, PA) and 3cyanopropyltriethoxysilane was purchased from Gelest (Morrisville, PA). 3.2.3 Preparation of sol-gel CN-PDMS c oated microextraction capillaries Preparation of sol-gel coated microextra ction capillaries involves preparation of the sol solution, Pretreatment of the fused sili ca capillary, coating the pretreated capillary with the sol solution, and post coating treatment. 3.2.3.1 Preparation of sol solution The used sol solution consisted of an alkoxide precursor(s), a sol-gel-active (either hydroxy or alkoxy silane terminated ) organic polymer, surface deactivating reagent, appropriate organic so lvent, and a sol-gel catalyst. Table 3.1 presents the names, functions, and chemical structures of differen t chemical ingredients used to prepare the sol solution for creating the sol-gel CN-P DMS coated microextraction capillaries. A sol-gel coating solution was prepared as follows: First 50 mg of PDMS (sol-gel active polymer), and 50 L of 3-cyanopropyl triethoxysilane (sol-g el precursor) and

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111 Table 3.1 Names, functions, and chemical structures of sol–gel CN-PDMS coating solution ingredients. Name of chemical Function Structure 3-cyanopropyltriethoxysilane Sol-gel precursor Si OC2H5 OC 2 H 5 C2H5O CN Tetraethoxysilane (TEOS) Sol-gel co-precursor Si OC2H5 OC2 H 5 C2H5O OC2 H 5 Silanol-terminated poly(dimethylsiloxane) (PDMS) Sol-gel active polymer Si CH3CH3 n OH HO Trifluoroacetic acid / 5% water (v/v) Catalyst and source of water CF3COO H Solvent Dichloromethane CH2Cl2 1,1,1,3,3,3hexamethyldisilazane (HMDS) Deactivating reagent Si C H 3 H3C CH3 N Si C H 3 CH3 CH3 H

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112 50 L TEOS (sol-gel co-precursor) were disso lved in 700 L dichloromethane (solvent) contained in a polypropylene microcentrifug e vial. Subsequently, 10 L of HMDS (surface deactivation reagent) and 50 L of TFA (sol-gel catalyst ) containing 5% water were added to the microcentrifuge vial a nd mixed for 2 minutes using a vortex shaker. The resulting solution was cen trifuged at 14 000 rpm (~ 15 915 g) for 5 min and clear supernatant of the sol solution was transferred to another clean vial. This sol solution was used to coat fused silica capillaries to be used further for capillary microextraction. 3.2.3.2 Pretreatment of fused silica capillary First, the fused silica capillary (~ 2 m) was rinsed sequentially with dichloromethane (1 mL) and methanol (1 mL) using gas pressure-operated capillary filling/purging device (Figure 2.3) to clean th e capillary inner surface off any organic contaminants. The rinsed capillary was then purged with helium (50 psi) for 30 min followed by hydrothermal treatment. Hydrothermal treatment is a very important step that helps generating adequate surface silanol gr oups required for the formation of strong chemical bonds between the substrate and the developed sol-gel coating. To perform hydrothermal treatment, the cleaned fused sili ca capillary was filled with deionized water using the filling/purging device and after 15 mi n of in-capillary residence time the water was flushed out of the capillary with the aid of helium gas pressure (50 psi). The capillary was then purged with helium gas for 30 min so that only a thin layer of water remained on the inner surface of the capill ary. At this point, both the ends of the fused silica

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113 capillary were sealed with an oxy-acetylene torch and the sealed capillary was heated at 250 C in a GC oven for 2 hours. Under thes e conditions, additiona l silanol groups are generated on the fused silica capillary surface as a result of the hydrolysis of siloxane bridges. Following this, both the ends of the capillary were cut open with a ceramic wafer. One end of the fused silica capillary was then connected to the GC injection port with the help of a graphite ferrule a nd the capillary was heated again in the GC oven at 250 C for 2 hours under continuous helium flow (1 mL/m in) through the capillary. After this, the capillary was ready for coating. 3.2.3.3 Coating of the fused silica capillary with sol solution A hydrothermally treated [31] fused sili ca capillary (2 m) was filled with the freshly prepared sol solution using a helium (50 psi) pressure-operated filling/purging device (Figure 2.4). The sol solution was allo wed to stay inside the capillary for a controlled period of time (typica lly 10-15 minutes) to facilitate the formation of a sol-gel coating and its chemical bonding to the capilla ry inner walls. The residence time of the sol solution inside the capillary must be car efully controlled. A systematic study on the gelation time of sol solution was conducted to optimize the residence time of sol solution inside the fused silica capillary (Appendix B) After keeping the sol solution inside the capillary for the optimized period of ti me, the unbonded portion of the solution was expelled from the capillary under helium pressure (50 psi), leaving behind a surfacebonded sol-gel coating within the capillary. The sol-gel CN-PDMS co ated capillary was

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114 subsequently dried by purging with helium ( 50 psi) for an hour. The helium gas flow facilitated the evapora tion of liquids associat ed with the coating. 3.2.3.4 Post-coating treatment The purpose of post-coating tr eatment is to physically and chemically stabilize the sorbent coating on the fused silica capillar y surface and remove any residual non-bonded portion of sol solution from the capillary. For th is, the coated capillary was installed in a GC oven with one end of the capillary connect ed to the injection po rt and the other end left open in the GC oven. The sol-gel coated capillary was then thermally conditioned in the GC oven using temperatureprogrammed heating from 35 oC to 150 oC at 1 oC/min with a hold time of 300 min at 150 oC, simultaneously purging the capillary with helium (1 mL/min). The capillary was further conditioned from 150 oC to 300 oC at 2 oC/min, holding it at 300 oC for 60 min under helium flow (1 mL/min). Before using in extraction, the coated capillary was rinsed with 1 mL dichloromethane/methanol (1:1 v/v) mixtur e followed by purging with helium for 30-45 min to remove any residual solvent. Rinsing the capillary with the organic solvent helps clean the sol-gel coating surf ace. After rinsing, the capillary was conditioned again from 35 oC to 300 oC at 5 oC/min, holding it at 300 oC for 30 min under helium flow (1 mL/min). The conditioned capillary was then cu t into 12 cm long pieces that were further used in capillary microextraction.

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115 3.2.4 Preparation of the standard sample solution s for CME Stock solutions (10 mg/mL) of the selected analytes were prepared in methanol or THF and stored in surface-deactivated [30] amber glass vials. For extraction, fresh aqueous samples were prepared by further d iluting these stock solutions to ng/mL level concentrations. 3.2.5 Capillary microextraction of analytes on sol-gel CN-PDMS coated capillaries A Chromaflex AQ column (Knotes Gla ss, Vineland, NJ) was modified as described in ref. [30] and used for gravityfed sample delivery to the sol-gel CN-PDMS capillary for preconcentration by CME (Fi gure 3.1). A 12-cm long piece of thermally conditioned sol-gel CN-PDMS coated microe xtraction capillary (250 m i.d.) was vertically connected to the lower end of th e gravity-fed sample dispenser. The aqueous sample (50 mL) was poured into the dispen ser from its top end and allowed to flow through the microextraction capillary under gr avity. The extraction was carried out for 30-40 min for the analyte concen tration equilibrium to be es tablished between the sol-gel coating and the sample matrix. The capillary was then detached from the dispenser and the residual sample droplets were re moved by touching one of the ends of microextraction capillary with a piece of Kimwipes tissue. 3.2.6 GC analysis of the extracted analytes The extracted analytes were transferred fr om the microextraction capillary to the

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116 GC column via thermal desorption. The capillary was installed in the previously cooled (35 C) GC injection port, keepi ng ~ 3 cm of its lower end protruding into the GC oven (Figure 3.2). This end was then interfaced with the inlet of a GC capillary column using a deactivated two-way press–fit quartz connector Under splitless conditions, the extracted analytes were then thermally desorbed from the capillary by rapidly raising the temperature of the in jection port (from 30 oC to 300 oC at 60 oC/min), while keeping the GC oven temperature at 35 oC. Such a rapid temperature program of the injection port facilitated effective desorption of the extracted analytes from the sol-gel CN-PDMS microextraction capillary and their focusing at the GC analysis column inlet. Following this, the GC oven was temper ature programmed from 35 oC to 300 oC at rate of 20 oC/min to achieve separation of the focused analytes on the GC column. A flame ionization detector (FID) maintained at 350 oC was used for analyte detection. 3.2.7 Calculation of the limit of detect ion (LOD) for the extracted analytes The limit of detection (LOD) for an analyte is the lowest concentration that can be detected reliably. The LOD is related to bot h the signal and the noise of the analytical instrument and usually is defined as the con centration of the test analyte which gives a signal (S) three times the noise (N) of the analytical instru ment (i.e. concentration for which S/N ratio is 3:1). In order to calculate LOD, each analyte was extracted individually under same extraction conditions an d the peak height (signal) of the analyte was measured in milivolt (mV). The noise wa s measured in microvolt (V) from the

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117 Figure 3.2 Schematic representation of the conn ection of the microextraction capillary with the GC column inside the oven us ing a two-was press-fit quartz connector.

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118 baseline of the chromatogram using th e ChromPerfect for Windows (Version 3.5) computer software (Justice Laboratory So ftware, Mountain Views, CA). The limit of detection of the compound was calcu lated using the following equation. LOD = 3 x A n a l y t eco n e n t r a t i o n S / N (3.1) 3.2.8 Analyte enhancement factor for solgel CN-PDMS coated microextraction capillaries One of the major attributes of CME (or SPME) is its ability to preconcentrate the analytes(s) in the extracting phase, and therefor e, it is important to measure the analyte(s) enhancement factor for a particular extracti ng phase for a particular class of compounds. In order to measure extraction efficiency of the sol-gel CN-PDMS coated capillary, first, standard solutions of 1-undecanol, having 25-, 50-, 75-, 100-, 125, 150-, 175-, and 200 mg/L concentrations, were prepared in me thanol. One L of each of these standard solutions, having 0.025-, 0.050-, 0.075-, 0.100-, 0.125-, 0.150-, 0.175-, and 0.200 g of 1-undecanol, were injected individually into the GC injection port under splitless mode and the corresponding peak areas were recorded Figure 3.3 represents the standard curve for 1-undecanol. Direct extraction of 20 g/L aqueous solution of 1-undecanol was carried out using a 12-cm long piece of a sol-gel CN-PDM S microextraction capillary for 30 min.

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119 The peak area obtained for the extraction of 1-undecanol was recorded. Using the standard curve (Figure 3.3), the mass of 1undecanol extracted into the extracting phase was calculated. The volume of the sol-gel CN-PDMS co ating was calculated using the equation 3.2. Vc = 2 rdcL (3.2) Where, Vc = Volume of the sol-gel CN-PDMS coating. r = Inner radius of the extraction capillary. dc = Thickness of the coating. L = Length of the sol-gel CN-P DMS microextrac tion capillary. The volume of the sol-gel CN-PDMS coating (coating thickness ~ 1 m) in a 12-cm capillary (250 m i.d.) was calculated to be 0.188 L. The concentra tion of analyte (C) in the extracting phase was calcu lated using the equation 3.3. C = Mass of t he ana l y t ee x t r ac t edin t o t hecoa t in g volume of the coating (3.3) Finally, the analyte enhancement factor was calculated using equation 3.4. Enhacement Factor = Co n ce n t r a t i o n ofa n a l y t e i n t hecoa t i n g (C) Original concentration of analyte in the sample matrix (3.4)

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120 y = 552166x + 5326.2 R2 = 0.9778 0.0.E+00 2.0.E+04 4.0.E+04 6.0.E+04 8.0.E+04 1.0.E+05 1.2.E+05 1.4.E+05 0.0000.0500.1000.1500.2000.250 Mass (g)Peak area (arbitrary unit) Figure 3.3 Standard curve for 1-undecanol obtaine d by GC direct injection into the GC under splitless mode.

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121 The analyte enhancement factor for 1-undecanol was found to be 26,534 which is much higher than the values 353 and 915 obtaine d for the same compound on commercial PDMS (0.66 L) and PA (0.5 L) coated SPME fibers, respectively [32]. 3.3 Results and discussion In the sol-gel process, a gel can be fo rmed via hydrolytic polycondensation of a sol-gel precursor followed by aging and drying [33]. Since the introduction of sol-gel SPME coatings in 1997 [3], various sol-gel or ganic-inorganic hybrid materials have been prepared to coat SPME fibers [34,35] as well as inner walls of the fused capillaries for use in CME or in-tube SPME [30,36-38]. In this work, sol-gel chemistry was us ed to chemically bind highly polar cyanopropyl and nonpolar PDMS moieties to an evolving sol-gel network structure, and use such a hybrid organic-inorganic material as a surface-bonded coating in a fused silica capillary to provide efficient extraction of aqueous trace anal ytes from a wide range of polarity. 3.3.1 Reactions leading to the formation of a chemically immobilized sol-gel CNPDMS network In recent years, sol-gel t echnology has received increase d attention in analytical separations and sample preparations due to its outstanding versatility and excellent control over properties of the cr eated sol-gel materials that proved to be promising for use as stationary phases and extraction media. The chemical ingredients used the in sol

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122 solution to prepare sol-gel CN-PDMS coated mi croextraction capillaries are presented in Table 3.1. As can be seen in Table 3.1, the used sol solution contained 3cyanopropyltriethoxysilane (sol-g el precursor) and TEOS (sol-g el co-precurs or). It is well-known from the basic principles of solgel chemistry [39] th at such alkoxysilane compounds are capable of undergoing hydrolytic polycondensation reactions in the presence of a sol-gel catalyst. Under th e experimental conditions used, both 3cyanopropyltriethoxysilane and TEOS can get hydr olyzed in the presence of the sol-gel catalyst, trifluoroacetic acid (TFA), as presented in the reaction Scheme 3.1. Polycondensation of the hydrolyzed precursors and silanol-terminated PDMS would lead to a three-dimensional sol–gel network incorporating highly polar cyanopropyl and nonpolar PDMS moieties in the organic-inorga nic hybrid structure (Scheme 3.2 (A) and (B)). Fragments of this sol-gel network, especi ally the ones growing in the vicinity of the capillary walls, have the opportunity to get chemically anchored to the capillary inner surface via condensation with the surface silanol groups, lead ing to the formation of a surface-bonded sol–gel coating on the capill ary inner walls forming a surface-bonded extracting phase film (Scheme 3.3). In this work, hexamethyldisilazane (HMDS) was added to the sol solution fo r deactivating the residual silanol groups on the sorbent coating during the post-coating th ermal conditioning (Scheme 3.4).

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123 Si (OC2H5)4 Tetraethoxysilane m H2O Si (OC2H5)3 CN 3-cyanopropyltriethoxysilane Si (OC2H5)3 (OH) m CN TFA TFA m n H2O Si (OC2H5)4 m C2H5OH n C2H5OH (OH)n n where, n = 1, 2, 3, or 4 m = 1, 2, or 3 Scheme 3.1 Hydrolysis of 3-cyanopropyltriethoxysila ne (precursor) and tetraethoxysilane (co-precursor).

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124 l H2O Si (OC2H5)3 (OH)m CN m Si (OC2H5)4(OH)n n where, n = 1, 2, 3, or 4 m = 1, 2, or 3 x, y, l, j, p, q = positive integers O Si O Si O q O O CN O p j C2H5OH x y (A) (B) (C) Scheme 3.2-A Growth of sol-gel CN-PDMS polymer chains within a fused silica capillary via polycondensation of a hydrolyzed sol-gel precursor (A) and a hydrolyzed co-precursor (B).

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125 O Si O Si O q O O CN O p where, p, q, r, k = positive integers Si CH3CH3 r O H HO k H2O O Si O Si O q O O CN O p Si CH3CH3 r O (C) (D) Scheme 3.2-B Growth of sol-gel CN-PDMS polymer chains within the sol solution filling a fused silica capillary via polycondensat ion of precursors (C) and a sol-gel active polymer (D).

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126 O Si O Si O q O O CN HO p Si CH3CH3 r O S iO Si O Si O Si O O Si O Si O OH OH O s H2O Inner wall of fused silica capillary O S iO Si O Si O Si O O Si O Si O OH O O O Si O Si O q O O CN p Si CH3CH3 r O O OH OH where, p, q, r, s = positive integers Scheme 3.3 Sol-gel CN-PDMS coating chemically an chored to the inner walls of a fused silica capillary.

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127 S iO Si O Si O Si O O Si O Si O OH O O O Si O Si O q O O CN p Si CH3CH3 r O O Si CH3 H3C CH3 N Si CH3 CH3 CH3 H OH t where, p, q, r, t, u = positive integers u NH3 S iO Si O Si O Si O O Si O Si O O O O O Si O Si O q O O CN p Si CH3CH3 r O O O Si H3C CH3 CH3 Si H3C CH3 CH3 Scheme 3.4 Deactivation of sol-gel CN-PDMS coatin g chemically anchored to the inner walls of a fused silica capillary.

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128 3.3.2 Characterization of the surface mor phology and determination of the coating thickness of the sol-gel CN-PDMS coating in a CME capillary using scanning electron microscopy Surface morphology and thickness of sol-gel CN-PDMS coatings in microextraction capillaries we re investigated using s canning electron microscopy. Figures 3.4 and 3.5 represent scanning electron microscopic images of a sol-gel CNPDMS coated capillary in two different orie ntations at magnifications: 10,000x (Fig. 3.4) and 20,000x (Fig. 3.5). From figure 3.4 it is eviden t that coating thickness is uniform, and was estimated at 1 m. Figure 3.5 represents the surface morphology of the sol-gel CNPDMS coating obtained at 20,000x magnification. As can be seen from this SEM image, sol-gel CN-PDMS coating possess a roughened, porous structure. The porous structure provides enhanced surface area which in turn translates into improved sample capacity of sol-gel CN-PDMS coatings. 3.3.3 Thermaland solvent stabilities of so l-gel CN-PDMS coated microextraction capillaries Figures 3.6 and 3.7 illustrate the thermal stability of sol–gel CN-PDMS coatings in microextraction capillaries used for extrac tion of polar [Fig 3.6] and nonpolar [Fig 3.7] analytes. The GC peak areas of four extracted alcohols di d not show any significant changes after the CN-PDMS coated capillaries were stepwise conditi oned for 1 h at 290-, 300-, 310-, 320-, and 330 oC. The enhanced thermal stability can be attributed to the

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129 Figure 3.4 Scanning electron microscopic image of a sol-gel CN-PDMS coating on the inner surface of a fuse d silica capillary (250 m i.d.) used in CME illustrating uniform coating thickness; magnification: 10,000x.

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130 Figure 3.5 Scanning electron microscopic image of a sol-gel CN-PDMS coating on the inner surface of a fused silica capillary (250 m i.d.) used in CME illustrating porous fine structure of the sol-gel coating; magnification: 20,000x.

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131 strong chemical bonding between sol-gel CN-P DMS coating and the inner walls of the fused silica capillary. It should be noted th at the performance of the sol-gel CN-PDMS coated capillary with regard to extraction of alcohols wa s not affected even after subjecting it to a conditioning temperature of 330 C. When the microextraction capillary was heated above 330 C a reduction in peak area of extracted alcohols was observed. Since the polar cyanopropyl moieties are mainly responsible for the extraction of these polar analytes, it can be assumed that such a peak area reduction is associated with degradation of the cyanopropyl moiety in the sol-gel coating above 330 C. On the other hand, no significant change was observed in peak area of nonpolar compounds extracted with sol-gel CN-PDMS coated capillaries condi tioned up to 350 C. This indicates that the nonpolar PDMS component of the sol-gel coating (which is responsible for the extraction nonpolar analytes) was still intact even when the capillary was conditioned at 350 C. We are not aware of any reports on cyano moiety-containing surface coatings that can provide stable performan ce at such a high temperature (330 C). By comparison, even the thin conventionally prepared cya nopropylpolysiloxane based GC coatings (~ 0.25 m) that should, in principle, provide bett er thermal stability (compared to thicker coating like the ones used in the present wo rk) have upper temperature limit of ~ 275 C [40]. Addtionally, solgel CN-PDMS coating showed excel lent stability toward organic solvents. As it can be seen in Table 3.2, the performance of the sol-gel CN-PDMS capillary in CME remained practically unc hanged after rinsing it with 50 mL of dichloromethane/methanol mixture (1:1, v/v) over a 24 h period.

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132 0 1 2 3 4 5 6 7 8 290300310320330340350 Temperature (oC)Average Peak area (arbitrary unit) 1-heptanol 1-octanol 1-nonanol 1-decanol Figure 3.6 Effect of conditioning temperature on the performance of sol–gel CN-PDMS microextraction capillary in CME of alcohols used as test solutes. CME-GC conditions: extraction time, 30 min.; 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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133 0 1 2 3 4 5 6 7 8 290300310320330340350 Temperature (oC)Average Peak area (arbitrary unit) Acenaphthene Fluorene Phenanthrene Fluoranthene Figure 3.7 Effect of conditioning temperature on the performance of sol–gel CN-PDMS microextraction capillary in CME of PAHs used as test solutes. CME-GC conditions: extraction time, 30 min.; 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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134 Table 3.2 GC peak area repeatability data (n = 3) for free fatty acids obtained in CMEGC experiments conducted before and af ter rinsing the sol-gel CN-PDMS coated microextraction capillary with a mixture (50 mL) of dichloro methane/methanol (1:1, v/v) for 24 hours. Peak area Name of the analyte Before rinsing A1 (arbitrary unit) After rinsing A2 (arbitrary unit) Relative change in peak area (A) = | (A2-A1)/A1| • 100 (%) Hexanoic acid 11.9 11.5 3.4 Nonanoic acid 9.2 9.4 2.2 Decanoic acid 8.6 8.2 4.7

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135 3.3.4 Extraction profile of moderately pola r and highly polar organic compounds on sol-gel CN-PDMS coated CME capillary Figure 3.8 illustrates the extraction kinetics of valerophenone, 2,4,6trichlorophenol, 1-nonanol, a nd nonanoic acid on a sol-ge l coated microextraction capillary. The CME experiments were carried out using aqueous samples of individual test analytes. The extraction equilibriums for valerophenone and 2,4,6-trichlorophenol were reached faster (~ 20 minutes) than those for 1-nonanol and nonanoic acid (~ 30 minutes). These results indicate that, compared with 1-nonanol and nonanoic acid, valerophenone and 2,4,6-trichlorophenol have lower affinity for the aqueous matrix resulting in their faster ex traction. On the other hand, gr eater hydrophilic nature of 1nonanol and nonanoic acid makes the extraction process slower which is evident from longer equilibration time. 3.3.5 CME-GC analysis of non-polar, moderately polar, and highly polar organic compounds using sol-gel CN-PDMS c oated microextraction capillaries Sol-gel CN-PDMS coated capillaries were used to extract a variety of analytes from a wide polarity range (nonpolar to highl y polar) and of environmental, biomedical and ecological importance. Test analytes included polycyclic ar omatic hydrocarbons (PAHs), aldehydes, ketones, aromatic amines, phenols, alcohols and free fatty acids. The extracted solutes were furt her analyzed by GC-FID.

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136 0.0E+00 1.0E+04 2.0E+04 3.0E+04 4.0E+04 5.0E+04 6.0E+04 7.0E+04 8.0E+04 010203040506070Extraction time (min.)Peak area (arbitrary unit) Valerophenone Trichlorophenol Nonanol Nonanoic acid Figure 3.8 Illustration of the extraction profile of moderately polar (valerophenone, 20 g/L), and polar (2,4,6 -trichlorophenol, 200 g/L; 1-nonanol, 40 g/L; nonanoic acid, 200 g/L) analytes extracted on a 12 cm 250 m i.d. sol–gel CN-PDMS coated capillary from aqueous samples. Extraction c onditions: triplicate ex traction for 10, 20, 30, 40, 50, 60, and 70 min. GC analysis conditio ns: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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137 3.3.5.1 CME-GC-FID of polycyclic aromatic hydrocarbons using sol-gel CN-PDMS coated microextraction capillaries Polycyclic aromatic hydrocarbons are among the most common environmental pollutants found in air, water, and soil in the USA and other industrialized countries where petroleum products are heavily used. Due to their potential or proven carcinogenic activities, US Environmental Protection Agency (EPA) has placed 16 unsubstituted PAHs in its list of 129 priority polluta nts [41]. Among the 16 EPA promulgated unsubstituted PAH, 4 were extracted and analyzed using sol-gel CN-PDMS coated microextraction capillaries. Table 3.3 provides a list of 4 selected unsubstituted PAHs, their chemical structures as well as pert inent physico-chemical properties. Figure 3.9 represents a gas chromat ogram of unsubstituted polycyclic aromatic hydrocarbons extracted using a sol-gel CN-PDMS microextra ction capillary from an aqueous sample (12 g/L concentration of each). As can be s een from Table 3.4 and Table 3.5 the run-torun and capillary-to-capillary p eak area relative standard de viation (RSD) values for solgel CN-PDMS capillary were under 5% and 7%, respectively. The detection limits of ng/L were obtained for PAHs in the CME– GC–FID experiments us ing sol-gel CN-PDMS coated microextraction capillaries (Table 3.6). These values are better than the detection limits reported in the literature. For instan ce, detection limits obtained for fluorene (3.0 ng/L) and phenanthrene (3.1 ng/L) in our CM E-GC-FID experiments were lower than those reported by Zeng and co-workers [42] for same compounds (i.e. fluorene (5.6 ng/L) and phenanthrene (8.0 ng/L)) in HS-SPME-GC -FID experiments using sol-gel C{4}-OH-

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138 TSO coating. Also, Doong and co-workers [ 43] obtained a detection limit of 250 ng/L for fluoranthene by SPME-GC-FID on a commercial PDMS (100 m) coated fiber, which is much higher than the value 4.1 ng/L obtained for the same compound on sol-gel CNPDMS coated microextraction capillary in CME-GC-FID experiments. All data for detection limits were calculated us ing a signal-to-noi se ratio of 3.

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139 Table 3.3 Chemical structures and pertinent physic al properties of polycyclic aromatic hydrocarbons (PAHs) extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Acenaphthene 152.20 92.5 150 0.8987 Fluorene 166.22 114.8 295 1.203 Phenanthrene 178.23 99.2 340 0.9800 Fluoranthene 202.26 107.8 384 1.252

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140 Figure 3.9 CME–GC analysis of an aqueous samp le of PAHs. Extraction conditions: sol– gel CN-PDMS coated microextr action capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperat ure programmed from 35 oC to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) acenaphthene; (2) fluorene; (3) phenanthrene; and (4) fluoranthene.

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141 Table 3.4 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of PAHs extracted on a sol-gel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2 Run #3 Run #4 Run #5 RSD (%) Acenaphthene 6.6 6.3 6.5 6.6 6.3 2.4 Fluorene 5.9 5.6 5.8 6.0 5.8 2.3 Phenanthrene 6.9 6.3 6.7 6.9 6.3 4.2 Fluoranthene 5.9 5.4 5.7 5.7 5.6 3.6 Extraction conditions: Sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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142 Table 3.5 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary peak ar ea reproducibility for a mixture of PAHs extracted on a sol-gel CNPDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Acenaphthene 6.3 6.0 5.5 6.6 Fluorene 5.6 5.4 5.2 3.4 Phenanthrene 6.3 6.3 5.8 4.5 Fluoranthene 5.4 5.6 5.5 1.8 Extraction conditions: Sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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143 Table 3.6 Limits of detection (LOD) data for PAHs in CME-GC-FID using sol-gel CNPDMS microextraction capillaries. Measured Noise (V) : 1.523 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Acenaphthene 12 19.1 2.9 Fluorene 12 18.4 3.0 Phenanthrene 12 17.9 3.1 Fluoranthene 12 13.3 4.1 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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144 3.3.5.2 CME-GC-FID of aldehydes and keto nes using sol-gel CN-PDMS coated microextraction capillaries Aldehydes and ketones are known to have toxic and carcinogenic properties, and therefore, their presence in the environment is of great concern [44]. They are formed as by-products in the drinking water disinfection processes. Many of these by-products have been shown to be carcinogens or carcinogen suspects [45,46]. Due to the polar nature of these compounds, they are often derivatized [ 47] for GC analysis to avoid undesirable adsorption that leads to peak tailing and anal yte loss. Although analyt ical derivatizations are effective, they involve additional step s in the sample preparation scheme. These reactions may not be quantitative, especi ally for samples containing ultra trace concentrations of the analytes. They ma y also produce side products capable of interfering with the analysis. For these r easons, it is not always desirable to use derivatization of th e target analyte. We extracted four underivatized al dehydes using sol-gel CN-PDMS coated microextraction capillaries. List of these aldehydes is provided in Table 3.7. Figure 3.10 is a gas chromatogram representing CME-GC -FID analysis of a mixture of four underivatized aldehydes. Experimental data on replicate CME-GC-FID have been presented in Table 3.8, Table 3.9. It demons trates remarkable ab ility of sol-gel CNPDMS capillaries to reproducibly extract aldehydes from aqueous medium. We were also able to achieve detection limits (e.g., 0.002 g/L for nonanal and 0.005 g/L for dodecanal) lower than those reported in the literature for the same compounds (e.g., 0.33

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145 g/L for nonanal and 0.05 g/L for dodecanal) [38]. Table 3.10 represents the calculated detection limits for underivatized aldehydes. Table 3.11 provides a list of 5 ketones that were extracted from aqueous samples using sol-gel CN-PDMS coated capillaries. As can be seen from Figure 3.11, the sol-gel CN-PDMS coated capillaries were found to be effective in extracting four underivatized ketones from an aqueous sample. CME-GC-F ID results are presented in Table 3.12, Table 3.13. Excellent reproducibility for the cap illary microextraction of ketones (RSD values for run-to-run and capillary-to-capillary reproducibility were under 5 %) demonstrates the versatility of the sol–gel CN-PDMS coatings and the sol-gel procedure used to prepare the extraction capillaries. Als o, the detection limits of ng/L were obtained for ketone in the CME–GC–FID experi ments using sol–gel CN-PDMS coated microextraction capillaries (Table 3.14). These va lues are better than the detection limits reported in the literature. For instance, de tection limits obtained for hexanophenone (2.3 ng/L) and anthraquinone (4.7 ng/L) using sol-gel CN-PDM S coated microextraction capillaries were lower than those reported for same compounds (i.e. hexanophenone (109 ng/L) and anthraquinone (32 ng/L)) using sol-gel PDMS coated microextraction capillaries [30].

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146 Table 3.7 Chemical structures and pertinent physi cal properties of al dehydes extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Nonanal 142.24 -18 93 at 23 mm Hg 0.823 O 4-isopropyl benzaldehyde 148.20 235236 0.977 O 4-tertbutylbenzaldehyde 162.23 130 at 25 mm Hg 0.970 O Dodecanal 184.32 12 240 0.829 O

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147 Figure 3.10 CME–GC analysis of aldehydes. Ex traction conditions: sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) nonanal, (2) 4isopropylbenzaldehyde, (3) 4-tert-but ylbenzaldehyde, and (4) dodecanal.

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148 Table 3.8 Experimental data of CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of aldehydes extracted by CME on a sol-gel CNPDMS microextraction capillary. Name of Analyte GC Peak Area (arbitrary unit) Run #1Run #2 Run #3 Run #4 Run #5 RSD (%) Nonanal 5.9 6.2 6.0 5.9 5.9 2.2 4-isopropylbenzaldehyde 4.3 4.9 4.4 4.4 4.3 4.8 4-tert-butylbenzaldehyde 8.9 9.4 8.8 8.6 8.7 3.6 Dodecanal 6.8 7.0 7.0 6.5 6.4 4.2 Extraction conditions: sol–gel CN-PDMS co ated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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149 Table 3.9 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary peak area reproduc ibility for a mixture of aldehydes extracted on a sol-gel CN-PDMS microextr action capillary. Name of Analyte GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Nonanal 6.2 6.5 6.3 2.8 4-isopropylbenzaldehyde 4.9 5.0 5.3 4.6 4-tert-butylbenzaldehyde 9.4 10.0 9.7 3.3 Dodecanal 7.0 6.5 6.2 5.5 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm). extraction time, 30 min., GC analysis c onditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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150 Table 3.10 Limits of detection (LOD) data fo r aldehydes in CME-GC-FID experiments using sol-gel CN-PDMS micr oextraction capillaries. Measured Noise (V) : 1.134 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Nonanal 80 16.2 16.8 4-isopropylbenzaldehyde 100 15.2 22.4 4-tert-butylbenzaldehyde 80 20.7 13.1 Dodecanal 40 11.3 12.0 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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151 Table 3.11 Chemical structures and pe rtinent physical properties of ketones extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Butyrophenone 148.20 11 13 220222 0.988 O Valerophenone 162.23 -9 105 107 at 5 mm Hg 0.988 O Hexanophenone 176.26 25 26 265.1 0.958 O Benzophenone 182.22 48.5 305.4 1.11 O Anthraquinone 208.22 286 380 1.438 O O

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152 Figure 3.11 CME–GC analysis of ketones. Extraction conditions: sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) butyrophenone, (2) valerophenone, (3) hexanophenone, (4) benzopheno ne, and (5) anthraquinone.

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153 Table 3.12 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of ketones extracted on a sol-gel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) Butyrophenone 3.4 3.4 3.3 3.3 3.4 1.9 Valerophenone 5.5 5.6 5.5 5.4 5.0 4.0 Hexanophenone 8.7 9.1 9.2 8.7 8.1 5.0 Benzophenone 5.8 5.9 5.8 5.7 5.4 3.2 Anthraquinone 5.3 5.4 5.7 5.7 5.9 4.0 Extraction conditions: sol–gel CN-PDMS co ated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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154 Table 3.13 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary peak area reproduc ibility for a mixture of ket ones extracted on a sol-gel CNPDMS microextraction capillary. Name of Analytes Peak Area from capillary-to-capillar y (arbitrary units) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Butyrophenone 3.4 3.6 3.4 4.0 Valerophenone 5.6 5.5 6.0 3.8 Hexanophenone 9.1 8.5 8.6 4.0 Benzophenone 5.9 6.2 6.4 4.2 Anthraquinone 5.4 5.9 5.6 4.5 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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155 Table 3.14 Limits of detection (LOD) data for ketones in CME-GC-FID experiments using sol-gel CN-PDMS micr oextraction capillaries. Measured Noise (V) : 1.152 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Butyrophenone 30 14.7 7.0 Valerophenone 20 25.7 2.7 Hexanophenone 20 29.9 2.3 Benzophenone 20 20.3 3.4 Anthraquinone 30 21.9 4.7 Extraction conditions: sol–gel CN-PDMS co ated extraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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156 3.3.5.3 CME-GC-FID of Aromatic amines using sol-gel CN-PDMS coated microextraction capillaries Aromatic amines are used as intermedia tes in the pharmaceu tical, photographic, dye, and pesticide industries [48-50]. They have also been employed in rubber industry as antioxidants and antiozonants [51]. Many of the aromatic amines found in air, water and soil [52-55], have been classi fied as mutagenic and carc inogenic [56,57]. This makes quantitative detection of arom atic amines very important. In our study, various aromatic amines were directly extracted from aqueous samples (Table 3.15). Figure 3.12 represents a gas chromatogram of a mixture of four underivatized aromatic amines extracted from an aqueous sample. CME–GC–FID experiments using sol–gel CN-PDMS microextr action capillaries provided excellent runto-run (Table 3.16) and capillar y-to-capillary (T able 3.17) extraction repeatability characterized by RSD values of less than 5% We were also able to achieve lower detection limits (e.g., 0.11 g/L for N,N-dimethylaniline and 0.03 g/L for benzanilide, by CME-GC-FID) compared to othe r literature reports (e.g., 1.2 g/L for N,Ndimethylaniline, by HS-SPME-GC-FID [58] and 0.005 g/L for benzanilide, by CMEGC-FID [30]). LOD results for the aroma tic amines are provided in Table 3.18.

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157 Table 3.15 Chemical structures and pertinent phys ical properties of aromatic amines extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound N,Ndimethylaniline 121.18 2.45 194 0.956 N N-butylaniline 149.24 -12 241 0.931 NH Acridine 179.22 107 346 N Benzanilide 197.24 163 117 at 10 mm Hg N H O

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158 Figure 3.12 CME–GC analysis of aromatic amin es. Extraction conditions: sol–gel CNPDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) N,N-dimethylaniline, (2) Nbutylaniline, (3) acridine, and (4) benzanilide.

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159 Table 3.16 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of ar omatic amines extracted on a sol-gel CNPDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) N,N-dimethylaniline 8.9 8.5 8.3 8.5 8.4 2.4 N-butylaniline 11.3 11.1 11.0 10.9 11.1 1.3 Acridine 8.5 8.2 8.2 8.2 8.3 1.6 Benzanilide 9.8 9.6 10.3 10.4 10.3 3.6 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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160 Table 3.17 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary peak area reproducibility for a mixture of arom atic amines extracted on a solgel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary units) Capillar y #1 Capillary #2 Capillary #3 RSD (%) N,N-dimethylaniline 8.3 8.7 9.1 4.1 N-butylaniline 11.0 11.9 11.6 3.8 Acridine 8.2 9.0 8.7 5.0 Benzanilide 10.3 10.8 11.1 3.9 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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161 Table 3.18 Limits of detection (LOD) data for aromatic amines in CME-GC-FID experiments using sol-gel CN-PDM S microextracti on capillaries. Measured Noise (V) : 1.046 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) N,N-dimethylaniline 800 21.9 114.9 N-butylaniline 100 27.4 11.4 Acridine 100 30.1 10.4 Benzanilide 300 26.2 35.9 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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162 3.3.5.4 CME-GC-FID of chlorophenols using sol-gel CN-PDMS coated microextraction capillaries Chlorophenols (CPs) have been widely used as preservatives, pesticides, antiseptics, and disinfectants [59]. They are also used in producing dyes, plastics and pharmaceuticals. In the environment, CPs ma y also form as a result of hydrolysis, oxidation, and microbiological degr adation of chlorinated pesticides. As a result, CPs are often found in waters [60], soils, and sedime nts [61]. CPs constitute an important group of priority toxic pollutants li sted by EPA [41] because of their possible carcinogenic properties. In our study, four CPs were extracted using sol-gel CN-PDMS coated capillaries (Table 3.19). CPs are highly polar compounds with signifi cant affinity toward water. CN-PDMS coated capillaries were eff ective in extracting four underivatized CPs from an aqueous sample. A gas chromatogram obtained in these experiments is shown in Figure 3.13. Run-to-run and capillary-to-capillary microextraction reproducibility results are provided in Table 3.20 and Table 3.21, re spectively. We were able to achieve detection limits (e.g., 0.1 g/L for 2,4-dichlorophenol, by CM E-GC-FID) comparable to other literature reports (e.g., 0.1 g/L for the same compound, by SPME-GC-FID) [35,62,63]. In one instance, the detection limits were much lower than (e.g., 0.2 g/L for 2,4,6-trichlorophenol and 0.06 g/L for 4-chloro-3-methylphenol, by CME-GC-FID) the reported literature values (e.g., 60 g/L for 2,4,6-trichlorophenol and 53 g/L for 4chloro-3-methylphenol, by SPME-GC -FID) using commercial PA (85 m) coated fiber [64]. LOD results for CPs are provided in Table 3.22.

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163 Table 3.19 Chemical structures a nd pertinent physical prope rties of chlorophenols extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound 2,4dichlorophenol 163.0 45 210 1.383 C l Cl OH 2,4,6trichlorophenol 197.45 69.5 244.5 1.49 Cl C l Cl OH 4-chloro-3methylphenol 142.58 67 235 1.271 C l OH Pentachloro phenol 266.34 174 310 1.979 Cl Cl C l Cl Cl OH

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164 Figure 3.13 CME–GC analysis of chlorophenols Extraction conditio ns: sol–gel CNPDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 2,4-di chlorophenol, (2) 2,4,6trichlorophenol, (3) 4-ch loro-3-methylphenol, and (4) pentachlorophenol.

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165 Table 3.20 Experimental data on CME-GC replicat e measurements for run-to-run peak area reproducibility for a mixture of ch lorophenols extracted on a sol-gel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) 2,4-dichlorophenol 5.9 5.6 5.7 5.6 5.3 4.1 2,4,6-trichlorophenol 5.1 5.1 4.7 4.9 4.7 4.0 4-chloro-3-methylphenol6.8 6.8 6.1 6.9 6.6 5.0 Pentachlorophenol 5.7 5.2 5.5 5.9 5.2 4.5 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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166 Table 3.21 Experimental data on CME-GC replicates measurements illustrating capillary-to-capillary peak ar ea reproducibility for a mixture of chlorophenols extracted on a sol-gel CN-PDMS micr oextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) 2,4-dichlorophenol 5.7 6.0 6.2 4.6 2,4,6-trichlorophenol 4.7 4.6 4.2 5.8 4-chloro-3-methylphenol6.1 6.5 6.8 5.8 Pentachlorophenol 6.5 7.0 6.5 3.7 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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167 Table 3.22 Limits of detection (LOD) data for chlorophenols in CME-GC-FID experiments using sol-gel CN-PDM S microextracti on capillaries. Measured Noise (V) : 1.016 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) 2,4-dichlorophenol 600 13.4 136.9 2,4,6-trichlorophenol 500 9.4 161.5 4-chloro-3-methylphenol 300 16.1 56.9 Pentachlorophenol 200 15.6 39.1 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 10 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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168 3.3.5.5 CME-GC-FID of alcohols using solgel CN-PDMS coated microextraction capillaries Figure 3.14 represents a ga s chromatogram for a mixture of alcohols. These highly polar analytes were extracted from aqueous samples without any derivatization, pH adjustment or salting-out procedures. The presented data shows excellent affinity of the sol–gel CN-PDMS coating toward these highl y polar analytes that are often difficult to extract from aqueous media in underivatiz ed form using commercial coatings. Small RSD values for run-to-run (Table 3.24) and capillary-to -capillary (Table 3.25) peak area repeatability (< 6%) demonstrate outstanding performance of the sol–gel CN-PDMS coating. Moreover, the detection limits of low ng/L achieved in CME-GCFID experiments are quite remarkable (Table 3.26). Thes e values (e.g., 0.06 g/L for 1heptanol and 0.004 g/L for 1-octanol, by CME-GC-FID) were comparable to the values reported in the li terature (e.g., 0.02 g/L for 1-heptanol and 0.01 g/L for 1-octanol, by HS-SPME-GC-FID) [65]. Excellent symmetrical peak shapes and lo w limits of detecti on are indicative of outstanding performance of the used sol-ge l CN-PDMS coating in CME and excellent deactivation characteristics of sol-gel PDMS column used in the GC analysis of the extracted alcohols.

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169 Table 3.23 Chemical structures and pertinent phys ical properties of alcohols extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound 1-heptanol 116.20 -36 176 0.823 OH 1-octanol 130.23 -15 195 0.826 OH 1-nonanol 144.26 -8 to -6 215 0.828 OH 1-decanol 158.28 6 230 0.829 OH

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170 Figure 3.14 CME–GC analysis of alcohols. Ex traction conditions: sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 1-heptanol, (2) 1-octanol, (3) 1-nonanol, and (4) 1-decanol.

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171 Table 3.24 Experimental data on CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of alcohols extracted on a sol-gel CN-PDMS coated microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) 1-heptanol 2.8 2.9 2.6 2.8 2.6 5.2 1-octanol 3.9 4.0 3.6 3.8 3.8 4.2 1-nonanol 5.4 5.6 5.4 5.1 5.5 3.5 1-decanol 3.9 4.1 3.6 3.7 4.0 5.3 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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172 Table 3.25 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary peak area reproducib ility for a mixture of alcohols extracted on a sol-gel CNPDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) 1-heptanol 2.6 2.8 2.8 4.6 1-octanol 3.6 3.3 3.2 5.3 1-nonanol 5.4 5.1 5.5 4.4 1-decanol 3.6 3.9 3.5 5.9 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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173 Table 3.26 Limits of detection (LOD) data for alcohols in CME-GC-FID experiments using sol-gel CN-PDMS micr oextraction capillaries. Measured Noise (V) : 1.032 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) 1-heptanol 400 20.5 60.3 1-octanol 100 72.6 4.3 1-nonanol 40 78.8 1.6 1-decanol 20 44.4 1.4 Extraction conditions: so l-gel CN-PDMS coated microext raction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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174 3.3.5.6 CME-GC-FID of free fatty acid s using sol-gel CN-PDMS coated microextraction capillaries The determination of free fatty acids in va rious matrices such as blood plasma and urine is of great importance because they are key metabolites and intermediates in biological processes [66]. They are widely dispersed in nature and are often produced from humic substances during water tr eatment [67]. Being very hydrophilic, underivatized short-chain fatty acids are usually difficult to extract from aqueous atrices. In the present study, sol-gel CN-PDMS microextraction ca pillaries provided efficient extraction of fatty acids from aqueous samples without requiring any derivatization, pH adjust ment or salting-out procedures. A list of these free fatty acids is given in Table 3.27. A gas chromatogram obtained in these experiments is shown in Figure 3.15. Experimental data for free fatt y acids is presente d in Table 3.28, 3.29, and 3.30. It demonstrates remarkable ability of sol-gel CN-PDMS capillaries to reproducibly extract fatty acids from aqueous medium. Detection limits of 0.2 g/L and 0.01 g/L were obtained in CME-GC-FID experime nts for underivatized hexanoic acid and decanoic acid, respectively. These values are lo wer than those reported in the literature using in situ derivatization of fatty acids on polyacrylate coated SPME fiber (e.g., 0.5 g/L for hexanoic acid and 0.02 g/L for decanoic acid, by SPME-GC-FID) [5] and using sol-gel C[4] open chain crown et her/OH-TSO coated SPME fibers (e.g., 0.4 g/L for hexanoic acid and 0.03 g/L for decanoic acid, by SPME-GC-FID) [65].

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175 Table 3.27 Chemical structures and pertinent phys ical properties of free fatty acids extracted by CME using sol-gel CN-PDMS coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Hexanoic acid 116.16 -3 202 203 0.927 O OH Nonanoic acid 158.24 9 254 0.906 O OH Decanoic acid 172.27 31 32 268 270 0.901 O OH Undecanoic acid 186.29 28 31 228 at 160 mm Hg O OH

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176 Figure 3.15 CME–GC analysis of free fatty aci ds. Extraction conditions: sol–gel CNPDMS coated microextract ion capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. so l–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) hexanoic acid, (2) nonanoic acid, (3) decanoic acid, and (4) undecanoic acid.

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177 Table 3.28 CME-GC replicate measurements illustrating run-to-run peak area reproducibility for a mixture of free fatty acids extracted on a sol-gel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) Hexanoic acid 4.6 4.8 5.0 4.4 4.8 4.6 Nonanoic acid 6.1 6.2 5.9 6.3 5.9 3.2 Decanoic acid 4.2 4.1 4.6 4.5 4.1 5.1 Undecanoic acid 5.1 5.2 4.9 5.5 4.9 5.3 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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178 Table 3.29 CME-GC replicates measurements illu strating capillary-to-capillary peak area reproducibility for a mixture of free fatty acids extracted on a sol-gel CN-PDMS microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Hexanoic acid 5.1 4.9 5.3 4.0 Nonanoic acid 5.9 6.2 5.7 4.4 Decanoic acid 4.6 4.9 4.9 4.1 Undecanoic acid 4.9 5.4 5.2 4.2 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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179 Table 3.30 Limits of detection (LOD) data for free fatty acids in CME-GC-FID experiments using sol-gel CN-PDM S microextracti on capillaries. Measured Noise (V) : 1.011 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Hexanoic acid 600 9.2 197.2 Nonanoic acid 200 15.7 38.7 Decanoic acid 50 11.3 13.4 Undecanoic acid 50 16.3 9.3 Extraction conditions: sol–gel CN-PDMS coat ed microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC anal ysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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180 3.3.5.7 CME-GC-FID of a mixture of nonpolar, moderately polar and highly polar organic compounds using a sol-gel CN-PD MS coated microextraction capillary A mixture containing analytes from different chemical classes representing a wide polarity range was extracted from an aqueous sample using a sol-gel CN-PDMS coated capillary. As is revealed from the chro matogram (Figure 3.16), a sol-gel CN-PDMS coated capillary can be effectively used to simultaneously extrac t nonpolar, moderately polar, and highly polar compounds from an aqueous matrix. 3.3.5.8 Performance of sol-gel CN-PDMS capillary in CME Finally, the extraction performance of sol-gel CN-PDMS capillary was compared with the sol-gel PDMS capillary. Figures 3.17 and 3.18 compares the extraction of an aqueous sample containing two alcohols and two free fatty acids obtained on two sol-gel coated microextraction capillaries: a solgel CN-PDMS capillary [Figure 3.17] and a solgel PDMS capillary [Figure 3.18]. It is evident from these figur es that in the absence of highly polar moieties (such as cyanopropyl), the sol-gel PDMS coating alone cannot compete with water to provide extraction of hi ghly polar analytes like free fatty acids and alcohols.

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181 Figure 3.16 CME–GC analysis of a mixture of nonpolar, moderately polar and highly polar organic compounds. Extraction conditions: sol–gel CN-PDMS coated microextraction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 300 oC at a rate of 15 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 1-heptanol, (2) 2,4-dichlorophenol, (3) decanal, (4) nonanoic acid, (5) fluorene, and (6) acridine.

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182 Figure 3.17 CME–GC analysis of a mixture of two alcohols and two free fatty acids using a sol-gel CN-PDMS microext raction capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperat ure programmed from 35 oC (5 min) to 300 oC at a rate of 15 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 1-heptanol, (2) 1-octanol, (3) octanoic acid, (4) nonanoic acid.

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183 Figure 3.18 CME–GC analysis of a mixture of two alcohols and two free fatty acids using a sol-gel PDMS microextr action capillary (12 cm x 250 m i.d.), extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 300 oC, programmed at a rate of 60 oC/min; GC oven temperat ure programmed from 35 oC (5 min) to 300 oC at a rate of 15 oC/min; helium carrier gas; FID temperature 350 oC.

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184 3.4 Conclusion For the first time, sol–gel CN-PDMS coat ed microextraction capillaries were developed for effective preconcentration a nd trace analysis of polar and non-polar compounds. In such coatings, the cyanopropyl moieties are primarily responsible for the extraction of polar analytes and the PDMS moieties are mainly responsible for the extraction of nonpolar analytes. In conjunc tion with GC-FID, th e sol-gel CN-PDMS coated microextraction capillaries provided lo w ng/L level detection limits for polar and nonpolar analytes directly extr acted from aqueous media wi thout requiring derivatization, pH adjustment, or salting out procedur es. The sol-gel CN-PDMS microextraction coatings possess remarkable performance repeatability. The run-to-run and capillary-tocapillary peak area RSD values for thes e coatings were lowe r than 5% and 6%, respectively. The sol-gel CN-PDMS coatings showed excellent thermal and solvent stability. The integrity of the sol-gel CN -PDMS coatings and hence their extraction abilities for polar analytes was fully preserved even after conditioning at 330 oC.

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185 3.5 References to chapter 3 [1] J. Pawliszyn, Solid Phase Microextr action: Theory and Practice, Wiley-VCH, New York, 1997. [2] L.G. Blomberg, J. Microcol. Sep. 2 (1990) 62. [3] S.L. Chong, D. Wang, J.D. Hayes, B.W. Wilhite, A. Malik, Anal. Chem. 69 (1997) 3889. [4] D. Wang, S.L. Chong, A. Ma lik, Anal. Chem. 69 (1997) 4566. [5] L. Pan, M. Adams, J. Pawliszyn, Anal. Chem. 67 (1995) 4396. [6] B.J. Hall, J.S. Brodbelt, J. Chromatogr. A 777 (1997) 275. [7] S.-P. Yo, Chemosphere 38 (1999) 823. [8] M. Abalos, J.M. Bayona, J. Pawliszyn, J. Chromatogr. A 873 (2000) 107. [9] O.E. Mills, A.J. Broome ACS Symp. Ser. 705 (1998) 85. [10] V. Mani, Applications of Solid Phase Microextraction, Royal Society of Chemistry, Cambridge, UK, 1999. [11] M. Liu, Z. Zeng, B. Xiong, J. Chromatogr. A 1065 (2005) 287. [12] M. Liu, Z. Zeng, Y. Tian, Anal. Chim. Acta 540 (2005) 341. [13] K. Markides, L. Blomberg, J. Buijten, T. Wannman, J. Chromatogr. 254 (1983) 53. [14] L. Blomberg, K. Markides, T. Wannman, J. Chromatogr. 203 (1981) 217. [15] P. Sandra, M. Van Roelenbosch, I. Temmerman, M. Verzele, Chromatographia 16 (1982) 63. [16] B.A. Jones, J.C. Kuei, J.S. Bradshaw, M.L. Lee, J. Chromatogr. 298 (1984) 389. [17] B.E. Rossiter, S.L. Reese, S. Morga n, A. Malik, J.S. Bradshaw, M.L. Lee, J. Microcol. Sep. 4 (1993) 521. [18] A. Malik, I. Ostrovsky, S.R. Sumpter, S. L. Reese, S. Morgan, B.E. Rossiter, J.S. Bradshaw, M.L. Lee, J. Microcol. Sep. 4 (1993) 529.

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186 [19] R.K. Gilpin, W.R. Si sco, Anal. Chem. 50 (1978) 1337. [20] C. Dewaele, M. Verzele, J. Chromatogr. 197 (1980) 189. [21] E. Gaetani, C.F. Laureri, A. Mangia, Ann. Chim. 69 (1979) 181. [22] A. Darin, E.R. Ziad, J. Chromatogr. A 1029 (2004) 239. [23] G. Musch, D.L. Massart, J. Chromatogr. 432 (1988) 209. [24] J.W. Kelly, L. He, J.T. Stew art, J. Chromatogr. 622 (1993) 291. [25] N.B. Smith, S. Mathialagan, K.E. Brooks, J. Anal. Toxicol. 17 (1993) 143. [26] W. Noll, Chemisty and Technology of Silicones, Academic press, New York, 1968. [27] B.W. Wright, P.A. Peaden, M.L. Lee, J. High Resolut. Chromatogr. Chromatogr. Commun. 5 (1982) 413. [28] S. Kulkarni, L. Fang, K. Alhooshani A. Malik, J. Chro matogr. A 1124 (2006) 205–216. [29] J.D. Hayes, A. Malik, J. Chromatogr. B 695 (1997) 3. [30] S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Alli, A. Malik, Anal. Chem. 74 (2002) 752. [31] C. Shende, A. Kabir, E. Townsend, A. Malik, Anal. Chem. 75 (2003) 3518. [32] A. Kabir, in, University of South Florida, Tampa, 2005, p. 299. [33] J. Fricke, R. Caps, Ultrastructure Processing of Advanced Ceramics, Wiley, New York, 1988. [34] A. Malik, S.L. Chong, Applications of Solid Phase microextraction, Royal Society of Chemistry, Cambridge, UK, 1999. [35] Z. Zeng, W. Qiu, Z. Hu ang, Anal. Chem. 73 (2001) 2429. [36] A. Kabir, C. Hamlet, K.S. Yoo, G.R. Newkome, A. Malik, J. Chromatogr. A 1034 (2004) 1.

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187 [37] T.Y. Kim, K. Alhooshani, A. Kabir, D.P. Fries, A. Mali k, J. Chromatogr. A 1047 (2004) 165. [38] K. Alhooshani, T.-Y. Kim, A. Kabir, A. Malik, J. Chromatogr. A 1062 (2005) 1. [39] C. Brinker, G. Schere r, Sol–Gel Science. The Physics and Chemistry of Sol–Gel Processing, Academic Press, San Diego, CA, 1990. [40] Supelco catalog (2006) 317. [41] L.H. Keith, W.A. Telliard, Environ. Sci. Technol. 13 (1979) 416. [42] X. Li, Z. Zeng, S. Gao, H. Li, J. Chromatogr. A 1023 (2004) 15. [43] R.-a. Doong, S.-m. Chang, Y.-c. Sun, J. Chromatogr. A 879 (2000) 177. [44] WHO, Air Quality Guidelines fo r Europe, WHO European, Copenhagen, 1987. [45] N.R. Council, Formaldehyde and Ot her Aldehydes: Board on Toxicology and Environmental Health Hazards, Nationa l Academy Press, Washington, DC, 1981. [46] G.D. Leikauf, Environmental Toxi cants:Human Exposures and Their Health Effects, Van Nostrand Reinhold, New York, 1992. [47] J. Nawrocki, I. Kalkowska, A. Dabrowska, J. Chromatogr. A 749 (1996) 157. [48] M.S. Reisch, Chem. Eng. News 66 (1988) 7. [49] J. Szadowski, J. Dyes Pigments 14 (1990) 217. [50] G. Sabbioni, H.-G. Neuma nn, Carcinogenesis 11 (1990) 111. [51] Encyclopedia of Occupa tional Health and Safety, International Labour Office, Geneva, 1983. [52] P.D. Santo, G. Moneti, M. Salvadori, C. Saltutti, A.D. Rosa, P. Dolara, Cancer Lett. 60 (1991) 245. [53] E. Ward, A. Carpenter, S. Markowitz, D. Roberts, W. Halperin, J. Natl. Cancer Inst. 83 (1991) 501. [54] G. Birner, H.G. Neuman n, Arch. Toxicol. 62 (1988) 110.

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188 [55] P.L. Skipper, X. Peng, C.K. Soohoo, S.R. Tannen-baum, Drug Metab. Rev. 26 (1994) 111. [56] ACGIH, Threshold Limit Values and Biological Exposure Indices, ACGIH-Press, Cincinnati, OH, 1999. [57] D.-D. Forschungsgemeinschaft, MAKand BATValues, VCH, Weinheim, 2000. [58] Y.-l. Fu, Y.-l. Hu, Y.-j. Zheng, G.-K. Li, J. Sep. Sci. 29 (2006) 2684. [59] V.H. Kitunen, R.J. Valo, M.S. Sa lkainoja-Salonen, Environ. Sci. Technol. 21 (1987) 96. [60] D. Puig, D. Barcelo, Tr ends Anal. Chem. 15 (1996) 362. [61] M.R. Lee, Y.C. Yeh, W.S. Hsia ng, B.H. Hwang, J. Chromatogr. A 806 (1998) 317. [62] D. Wang, J. Xing, J. Peng, C. Wu, J. Chromatogr. A 1005 (2003) 1. [63] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [64] M. Portillo, N. Prohibas, V. Salvad, B.M. Simonet, J. Chromatogr. A 1103 (2006) 29. [65] M. Liu, Z. Zeng, Y. Lei, H. Li, J. Sep. Sci. 28 (2005) 2306. [66] E. Fogelqvist, B. Josefsson, C. Roos J. High Resolut. Chromatogr. Chromatogr. Commun. 3 (1980) 568. [67] J.H. Brill, B.A. Narayanan, J.P. McCormick, Appl. Spectrosc. 45 (1991) 1617.

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189 CHAPTER 4 SOL-GEL IMMOBILIZE D SHORT CHAIN PO LYETHYLENE GLYCOL COATING FOR CAPILLA RY MICROEXTRACTION 4.1 Introduction Polyethylene glycols (PEGs) have long been used as polar stationary phases in gas chromatography (GC) [1-4]. The polar na ture of PEG makes it an excellent sorbent for extraction of the polar analytes that ar e usually difficult to extract from aqueous matrices using silicone-based coatings. In solid-phase microextraction (SPME), PEGs have been used to prepare composite coatin gs [5,6]; however, low thermal stability [7], susceptibility to degradation by oxygen [7], and narrow useful temperature range for GC operation (~ 70 C – 270 C) of widely used high molecular weight PEGs (e.g., Carbowax 20M) [7,8] are the major shortc omings. Often, free radical cross-linking reactions are employed to immobilize PEG coat ings on the substrate [9,10]. However, in many instances, only partial immobilization has been achieved [11]. When such coatings with lower thermal stability are coupled to GC, it may lead to problems like incomplete desorption and sample carryover. In recent years, sol-gel technology has pr oven effective in the immobilization of PEGs for their use in SPME [12-14], capillar y microextraction (CME also called in-tube

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190 SPME) [15], and GC stationary phase [16]. Th e key to the effective immobilization is the chemical anchoring of PEGs onto the fused silica surface. Thanks to this chemical bonding, sol-gel coatings possess high thermal a nd solvent stability [17]. In addition to this, sol-gel coatings usually give a porous structure which significantly increased the surface area of the extracting phase allowing the use of thinner coatings to achieve faster extraction and desired level of sample capac ity [18]. Also, sol-gel technology provides tunable selectivity of a sol-gel coating by changing th e relative proportions of organic and inorganic components of the used sol solution. Although, sol-gel technology has great prom ise for the preparation of thermally stable coatings, to date only high molecu lar weight PEGs have been successfully immobilized [12,14-16]. PEGs with higher molecular weights have lower polarity compared to their low molecular weight counter parts, which limits their ability to extract highly polar analytes from aque ous matrix at room temperature. Considering this problem, the goal of this research was to immobili ze low molecular weight PEG coatings using sol-gel chemistry. Here, we de scribe a sol-gel method for in situ immobilization of low molecular weight (short chain) PEG to provide a stable coating using N(triethoxysilylpropyl)-O-polyethylene oxide urethane (TESP) and demonstrate the effectiveness of the developed sol-gel PEG coatings for capill ary microextraction of polar analytes from aqueous samples.

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191 4.2 Experimental section 4.2.1 Equipment All the CME-GC experiments with sol-gel PEG coated capillaries were performed on a Shimadzu Model 17A GC (Shimadzu, Kyoto, Japan) equipped with a flame ionization detector (FID) and a split-splitless injector. A homebuilt, gas pressure-operated capillary filling/purging device [19] was used to perform a number of operations: (a) rinse the fused silica capillary with solvents (b) fill the extractio n capillary with sol solution, (c) expel the sol soluti on from the capillary at the end of sol-gel coating process, and (d) purge the capillary with helium A Barnstead Model 04741 Nanopure deionized water system (Barnstead/Thermolyne, Dubuque, IA) was used to obtain ~16.0 M water. An in-house designed liquid sample dispen ser [15] was used to perform CME via gravity-fed flow of the aqueous samples th rough the sol-gel PEG coated capillary. A model G-560 (Scientific Industr ies, Bohemia, NY) vortex sh aker was used to mix the coating solution ingredients. A ThermoIEC model Micromax microcentrifuge (Needham Heights, MA) was used to separate the sol solu tion from the precipitate (if any) at 14 000 rpm (~ 15 915 g). A JEOL model JSM-35 scan ning electron microscope (SEM) was used to investigate the surface morphology of sol-gel PEG coated capillaries. 4.2.2 Materials and chemicals N-(triethoxysilylpropyl)-Opolyethylene oxide urethane (TESP, 95%) was

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192 purchased from Gelest (Morrisville, PA). Fused silica capillary ( 250 m i.d.) with a protective polyimide coating on the external surface was purchased from Polymicro Technologies (Phoenix, AZ). HPLC-grade so lvents (dichloromethane, methanol, and tetrahydrofuran (THF)), Kimwipes tissue pa per, polypropylene microcentrifuge tubes (2.0 mL), and 7.0 mL borosilicate vials (used to store standard solutions) were purchased from Fisher Scientific (Pittsburgh, PA). Aldehydes (nonanal, decanal, undecanal, and dodecanal), ketones (4’-chloroacetophenone, valerophenone, hexanophenone, benzophenone, 2,3-dichloro-1,4-naphthoquinone), aniline derivatives (2-chloroaniline, 3ethylaniline, 3-bromoaniline, N-butylanilin e, N-phenylaniline), substituted phenols (2,4dimethylphenol, 3,4-dichlorophenol, 2,4,6-trichlorophenol, 2-tert-butyl-4methoxyphenol), fatty acids (octanoic acid, nonanoic acid, decanoic acid, undecanoic acid), methyltrimethoxysilane (MTMOS, 98%), and trifluoroacetic acid (TFA, 99%) were purchased from Aldrich (Milwaukee, WI). Alcohols (1-heptanol, 1-octanol, 1nonanol, 1-decanol) were purchased from Acros (Pittsburgh, PA). 4.2.3 Preparation of sol-gel PEG coated microextraction capillaries Preparation of sol-gel coat ed extraction capillaries involved following operations: (1) preparation of the sol solu tion, (2) pretreatment of fuse d silica capillary, (3) coating the fused silica capillary w ith the sol solution, and (4 ) post-coating treatment.

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193 4.2.3.1 Preparation of sol solution A sol solution designed to prepare a hybr id sol-gel organicinorganic coating consisted of an alkoxide precursor, a sol-ge l co-precursor with a bonded PEG moiety, an appropriate organic solvent (dichloromethane), and a sol-gel catalyst (trifluoroacetic acid). Table 4.1 presents the names, functions, and chemical structures of different chemical ingredients used to prepare the sol solu tion for creating the sol-gel PEG coated microextraction capillaries. A sol-gel coating solution was prepared as follows: First 100 L MTMOS (sol-gel precursor) and 50 mg of TESP (sol-gel co -precursor) were dissolved in 500 L dichloromethane (solvent) contained in a polypropylene micr ocentrifuge vial. Subsequently, 100 L of TFA (sol-gel cataly st) containing 10 % wate r was added to the microcentrifuge vial and mixed for 2 minutes using a vortex shaker. The resulting solution was centrifuged at 14 000 rpm (~ 15 91 5 g) for 5 min. The clear supernatant of the sol solution was transferred to another clean vial, and was further used to coat fused silica capillaries for use in capillary microextraction. 4.2.3.2 Pretreatment of fused silica capillary The main purpose of pretreatment of the fu sed silica capillary is to clean its inner walls and enhance the content of the surf ace silanol (Si-OH) groups, and thereby facilitate effective covalent bonding of the sol-gel sorbent materials to the fused silica substrate. For this, the fused silica capillary (~ 2 m) was first rins ed sequentially with

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194 Table 4.1 Names, functions, and chemical struct ures of sol–gel PEG coating solution ingredients. Name of chemical Function Structure Methyltrimethoxysilane (MTMOS) Sol-gel precursor Si OCH3 OC H 3 H3CO C H 3 N-(triethoxysilylpropyl)-Opolyethylene oxide urethane (TESP) Sol-gel active coprecursor with a bonded PEG moiety NH C O O (CH2CH2O)4-6 H SiOC2H5OC2H5 C2H5O Trifluroacetic acid / 10 % water (v/v) Catalyst and source of water CF3COO H Solvent Dichloromethane C H 2Cl2

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195 dichloromethane (1 mL) and methanol (1 mL) using gas pressure-operated capillary filling/purging device (Figure 2.3) to clean th e capillary inner surface off any organic contaminants. The rinsed capillary was then purged with helium (50 psi) for 30 min followed by hydrothermal treatment. To perf orm hydrothermal treatment, the cleaned fused silica capillary was filled with deionized water using the filling/purging device and after 15 min of in-capillary residence time the water was flushed out of the capillary with the aid of helium gas pressure (50 psi). The capillary was then purged with helium gas for 30 min so that only a thin layer of water rema ined on the inner surface of the capillary. At this point, both the ends of the fused sili ca capillary were sealed with an oxy-acetylene torch and the sealed cap illary was heated at 250 C in a GC oven for 2 hours. Under these conditions, additional silanol gr oups are generated on the fused silica capillary surface as a result of the hydrolysis of siloxane bridge s. Following this, bo th the ends of the capillary were cut open with a ceramic wafer. One end of th e fused silica capillary was then connected to the GC in jection port with the help of a graphite ferrule and the capillary was heated again in the GC oven at 250 C for 2 hours under continuous helium flow (1 mL/min) through the cap illary. After this, the capilla ry was ready for coating. 4.2.3.3 Coating of the fused silica capillary with sol solution A hydrothermally treated [16] fused sili ca capillary (2 m) was filled with the freshly prepared sol solution using a helium (50 psi) pressure-operated filling/purging device (Figure 2.4). The sol solution was allowe d to stay inside the capillary for 15

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196 minutes. During this residence period of th e sol solution inside the capillary, a sol-gel hybrid organic-inorganic polymeric network e volved within the sol solution, and part of it ultimately became bonded to the fused sili ca capillary inner surface via condensation reaction with surface silanol groups. The resi dence time of the sol solution inside the capillary must be carefully controlled. A systematic study on the gelation time of sol solution was conducted to optimize the reside nce time of sol soluti on inside the fused silica capillary (Appendix B). After keeping th e sol solution inside the capillary for the optimized period of time (~ 15 min), the unbonded portion of the solution was expelled from the capillary under helium pressure ( 50 psi), leaving behind a surface-bonded solgel coating within the capillary. The sol-gel PEG coated capillary was subsequently dried by purging with helium (50 psi) for an hour. The helium gas flow facilitated the evaporation of liquids asso ciated with the coating. 4.2.3.4 Post-coating treatment The purpose of post-coating tr eatment is to physically and chemically stabilize the sorbent coating on the fused silica capillar y surface and remove any residual non-bonded portion of sol solution from the capillary. For th is, the coated capillary was installed in a GC oven with one end of the capillary connect ed to the injection po rt and the other end left open in the GC oven. The sol-gel coated capillary was then thermally conditioned in the GC oven using temperatureprogrammed heating from 35 oC to 340 oC at 1 oC/min, holding it at 340 oC for 60 min under helium flow (1 mL/min).

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197 Before using in extraction, the coated capillary was rinsed with 1 mL dichloromethane/methanol (1:1 v/v) mixtur e followed by purging with helium for 30-45 min to remove any residual solvent. Rinsing the capillary with the organic solvent helps clean the sol-gel coating surf ace. After rinsing, the capillary was conditioned again from 35 oC to 340 oC at 5 oC/min, holding it at 340 oC for 30 min under helium flow (1 mL/min). The conditioned capillary was then cu t into 12 cm long pieces that were further used in capillary microextraction. 4.2.4 Preparation of the standard sample solutions for CME Stock solutions (10 mg/mL) of the selected analytes were prepared in methanol or THF and stored in surface-deactivated [15] amber glass vials. For extraction, fresh aqueous samples were prepared by further d iluting these stock solutions to ng/mL level concentrations. 4.2.5 Capillary microextraction of analytes on sol-gel PEG coated capillaries A Chromaflex AQ column (Knotes Gla ss, Vineland, NJ) was modified as described in ref. [15] and used for grav ity-fed sample delivery to the sol-gel PEG capillary for preconcentration by CME (Fi gure 3.1). A 12-cm long piece of thermally conditioned sol-gel PEG coated microextractio n capillary (250 m i. d.) was vertically connected to the lower end of the gravity-fed sample dispen ser. The aqueous sample (50 mL) was poured into the disp enser from its top end and allowed to flow through the

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198 microextraction capillary under gravity. The extraction was carried out for 30-40 min for the analyte concentration equilibrium to be established between the sol-gel coating and the sample matrix. The capillary was then de tached from the dispenser and the residual sample droplets were removed by touching one of the ends of micr oextraction capillary with a piece of Kimwipes tissue. 4.2.6 GC analysis of the extracted analytes The extracted analytes were transferred fr om the microextraction capillary to the GC column via thermal desorption. The capillary was installed in the previously cooled (35 C) GC injection port, keepi ng ~ 3 cm of its lower end protruding into the GC oven (Figure 3.2). This end was then interfaced with the inlet of a GC capillary column using a deactivated two-way press–fit quartz connector Under splitless conditions, the extracted analytes were then thermally desorbed from the capillary by rapidly raising the temperature of the in jection port (from 30 oC to 340 oC at 60 oC/min), while keeping the GC oven temperature at 35 oC. Such a rapid temperature program of the injection port facilitated effective desorption of the extracted analytes from the sol-gel PEG microextraction capillary and their focusing at the GC analysis column inlet. Following this, the GC oven was temper ature programmed from 35 oC to 320 oC at rate of 20 oC/min to achieve separation of the focused analytes on the GC column. A flame ionization detector (FID) maintained at 350 oC was used for analyte detection.

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199 4.2.7 Calculation of the limit of detect ion (LOD) for the extracted analytes The LOD is related to both the signal and the noise of the analytical instrument and usually is defined as the concentration of the test analyte which gives a signal (S) three times the noise (N) of the analytical instrument (i.e. concentration for which S/N ratio is 3:1). In order to calculate LOD, each analyte was extr acted individually under same extraction conditions and the peak height (signal) of the anal yte was measured in mV. The noise was measured in V from the baseline of the chromatogram using the ChromPerfect for Windows (Version 3.5) co mputer software (Justice Laboratory Software, Mountain Views, CA). The limit of detection of the compound was calculated using the equation 3.1. 4.2.8 Analyte enhancement factor for short chain sol-gel PEG coated microextraction capillaries Analyte enhancement factor [20] of the short chain sol-gel PEG coated capillary was measured using 1-undecanol as a test anal yte. The procedure has been described in chapter 3 (section 3.2.8). The analyte enha ncement factor was found to be 32,500 for a (12-cm x 250 m i.d.) sol-gel PEG coated microextraction capilla ry with a coating volume of 0.094 L. 4.3 Results and discussion Sol–gel chemistry provides an effective synthetic pathway for creating organic–

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200 inorganic hybrid materials of de sired properties. Due to it’s versatility, in recent years, it has been effectively utilized to create surface-bonded coatings on the outer surface of conventional SPME fibers [18,21,22] as well as on the inner walls of fused silica capillary for use in CME or in-tube SPME [15,23-26]. In the present work, sol-gel chemistry was used to immobilize a low molecular weight PEG on fused silica capillary inner surface creating sol-gel PEG coating which provided efficient extraction of moderately pol ar and highly polar aque ous trace analytes. 4.3.1 Reactions leading to the formation of a chemically immobilized sol-gel PEG network It is well-known from the basic princi ples of sol-gel chemistry [27] that alkoxysilane compounds are capable of un dergoing hydrolytic polycondensation reactions in the presence of a sol-gel catalyst. As can be s een in Table 4. 1, the used sol solution contained MTMOS (sol-gel precu rsor) and N-(triethoxysilylpropyl)-Opolyethylene oxide urethane (TESP) (sol-gel co-precursor with PEG moiety). TESP, which carries triethoxysilane groups at one end and hydroxyl terminated polyethylene oxide chain at other end, is th e key sol-gel active ingredient. The creation of sol-gel PEG coating invol ved following processe s: (1) hydrolysis of the alkoxysilane compounds, MTMOS and TESP (Scheme 4.1); (2) polycondensation of the hydrolyzed species with themselves and other sol-gel active ingredients in the sol solution (Scheme 4.2); and (3) chemical anchor ing of the evolving sol-gel network to the

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201 capillary inner surface via condensation with the surface silanol groups, leading to the formation of a surface-bonded sol–gel coating on the capillary inner walls (Scheme 4.3). In this research, trifluoroacetic acid wa s used to catalyze th e sol-gel reactions. 4.3.2 Determination of the thickness of the sol-gel PEG coating in a CME capillary using scanning electron microscopy The thickness of sol-gel PEG coatings in microextraction capillaries was investigated using scanning el ectron microscopy. Figure 4.1 represents side view of a scanning electron microscopic image of a sol-gel PEG coated capillary at 10,000x magnification. From Figure 4.1 it is evident th at coating thickness is uniform, and was estimated at 0.5 m.

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202 Si (OCH3)3 CH3 n CH3OH Si(OH)nC H 3 n H2O N-(triethoxysilylpropyl)-Opolyethylene oxide urethane Methyltrimethoxysilane Si(OH)n (OC2H5)3 NH C O O (CH2CH2O)4-6H Si (OC2H5)3 TFA TFA n H2O n (OCH3)3 n NH C O O (CH2CH2O)4-6H n C2H5OH where, n = 1, 2, or 3 (A) (B) Scheme 4.1 Hydrolysis of methyltrim ethoxysilane (precursor) and N(triethoxysilylpropyl)-O-polyethyl ene oxide urethane (sol-gel co-precursor with bonded PEG moiety).

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203 Si(OH)nCH3 n (OCH3)3 Si(OH)n (OC2H5)3 n NH C O O ( C H 2C H 2O)4-6 H l H2O j C2H5OH k CH3OH y x where, n = 1, 2, or 3 x, y l, j k, p q = p osi t ivei n t e g e r s O Si O Si O q O O p NH C O O (CH2CH2O)4-6H CH3 (B) (A) Scheme 4.2 Growth of sol-gel polymeric network within the sol solution filling a fused silica capillary via polycondensation of a hydrolyzed sol-gel precursor (A) and a hydrolyzed sol-gel co-precursor wi th a bonded PEG moiety (B).

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204 O Si O Si O q O HO p NH C O O ( CH2CH2O)4-6H CH3 S iO Si O Si O O Si O OH s H2O Inner wall of fused silica capillary O O where, p, q, s = positive integers S iO Si O Si O O Si O O O O O Si O Si O q O p NH C O O (CH2CH2O)4-6H CH3 Scheme 4.3 Sol-gel PEG coating chemically anchored to the inner walls of a fused silica capillary.

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205 Figure 4.1 Scanning electron microscopic image of a sol-gel PEG coating on the inner surface of a fused silica capilla ry (250 m i.d.) used in CME illustrating uniform coating thickness; magnification: 10,000x. Coating thickness Sol-gel PEG coating Magnification: 10,000x

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206 4.3.3 Thermaland solvent stabilities of sol-gel PEG coating The thermal stability of a sol–gel PEG coated microextraction capillary was evaluated using 1-octanol, 2,4-dimethylphe nol, decanal, and naphthylamine as test analytes. A sol-gel PEG coated capillary was stepwise condi tioned for 1 h at 290-, 300-, 310-, 320-, 330-, 340-, 350-, and 360 oC in the GC oven under helium flow (1 mL/min). As it can be seen from Figure 4.2, the GC pe ak areas of the extracted test analytes showed no significant changes even after the sol-gel PEG capillary was conditioned at 340 oC. The enhanced thermal stability can be attributed to the strong chemical bonding between sol-gel PEG coating and the inner wa lls of the fused silica capillary. Since the PEG moieties in the sol-gel coating are mainly responsible for the extraction of these analytes, the reduction in GC peak ar eas of extracted analytes above 340 oC can be attributed to degradati on of these PEG moieties. Sol–gel PEG coating showed excellent st ability toward organic solvents. Table 4.2 illustrates solvent stability of the sol–gel PEG coating. The performance of the sol– gel PEG coated capillary in CME remained practically unchanged after rinsing it with 50 mL of dichloromethane/methanol mi xture (1:1, v/v) over a 24 h period.

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207 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 290300310320330340350360 Temperature (oC)Average Peak Area (arbitrary unit) 1-octanol 2,4-dimethylphenol Decanal Naphthylamine Figure 4.2 Effect of conditioning temperatur e on the performance of sol–gel PEG microextraction capillary. CME-GC conditi ons: extraction time, 30 min.; 5 m 250 m i.d. sol–gel PDMS column; splitless injec tion; injector temperature: initial 30 oC, final (mentioned on x-axis), programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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208 Table 4.2 GC peak area repeatability data (n = 3) for alcohols obtained in CME-GC experiments conducted before and after rinsin g the sol-gel PEG coated microextraction capillary with a mixture (50 mL) of dichlo romethane/methanol (1:1, v/v) for 24 hours. Peak area Name of the analyte Before rinsing A1 (arbitrary unit) After rinsing A2 (arbitrary unit) Relative change in peak area (A) = | (A2-A1)/A1| • 100 (%) 1-Heptanol 6.5 6.7 3.1 1-Octanol 9.5 9.6 1.1 1-Nonanol 10.2 10.5 2.9

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209 4.3.4 Extraction profile of organic compounds on sol-gel PEG coated CME capillary Figure 4.3 illustrates extraction profile of two moderately polar compounds (nonanal and hexanophenone) and two highly pol ar compounds (1-octanol and nonanoic acid) on a sol-gel PEG coated microextract ion capillary. Both moderately polar and highly polar analytes reached equilibria with sol-gel PEG coating within 30 min indicating fast diffusion and high affinity of the used sol-gel PEG coating toward polar analytes. Based on these kinetic data, further experiments in this work were carried out using a 30 min extraction time. 4.3.5 CME-GC analysis of moderately pola r and highly polar organic compounds using sol-gel PEG microextraction capillaries Sol-gel PEG coated capillari es were used to extract moderately polar and highly polar analytes which usually are difficult to extract from aqueous matrices and of great importance in industrial, biomedical, and en vironmental areas. Test analytes included aldehydes, ketones, aromatic amines, phenol s, alcohols, and free fatty acids. The extracted solutes were fu rther analyzed by GC-FID.

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210 0.0E+00 1.0E+04 2.0E+04 3.0E+04 4.0E+04 5.0E+04 6.0E+04 7.0E+04 8.0E+04 9.0E+04 010203040506070Extraction time (min)Peak area (arbitrary unit) Nonanal Hexanophenone 1-octanol Nonanoic acid Figure 4.3 Illustration of the extraction profile s of moderately polar (nonanal and hexanophenone) and polar (1-nonanol and nonanoi c acid) analytes extracted on a 12 cm 250 m i.d. sol–gel PEG coated capillary from aqueous sa mples. Extraction conditions: triplicate extraction for 10, 20, 30, 40, 50, 60, and 70 min. GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless inj ection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temper ature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier ga s; FID temperature 350 oC.

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211 4.3.5.1 CME-GC-FID of aldehydes and ketones using sol-gel PEG coated microextraction capillaries Aldehydes and ketones (carbony l compounds) play an impor tant role in aquatic oxidation processes. They can form in wate r by the photodegradation of dissolved natural organic matter [28]. They are also major di sinfection by products formed as a result of chemical reaction between disinfectant (ozone or chlorine) and natura l organic matter in drinking water [29]. Several of these by-products have been shown to be carcinogens or carcinogen suspects [30,31]. This makes quan titative detection of carbonyl compounds very important. Analytical determination of aldehydes is often performed through derivatization into less polar or easy-to-detect forms [3 2]. In this work, aldehydes were extracted and analyzed without derivatization. We extracted four underivatized aldehydes using sol-gel PEG coated microextraction capi llary. List of these underivatized aldehydes is provided in Table 4.3. Figure 4.4 is a ga s chromatogram repres enting a mixture of 4 underivatized aldehydes. Microextraction result s have been presented in Table 4.4, Table 4.5. Table 4.6 represents the calculated detec tion limits for these underivatized aldehydes. We obtained detection limits of 20.4 ng/L, 11.8 ng/L, and 16.1 ng/L for nonanal, decanal, and undecanal, respectively, in CME-GC-FID experiments using sol-gel PEG coated microextraction capillaries. By comparison, these LOD values are better than those reported in the literature for the same com pounds extracted using sol-gel PDMS coated microexrtaction capillaries (i.e. 40.4 ng/L, 28.3 ng/L, and 50.4 ng/L for nonal, decanal, and undecanal, respectively) [15].

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212 Table 4.3 Chemical structures and pertinent physi cal properties of al dehydes extracted by CME using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Nonanal 142.24 -18 93 at 23 mm Hg 0.823 O Decanal 156.27 -6 207 209 0.825 O Undecanal 170.29 7-8 223 0.827 O Dodecanal 184.32 12 240 0.829 O

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213 Figure 4.4 CME–GC analysis of aldehydes. Extr action conditions: sol–gel PEG coated microextraction capillary (12 cm x 250 m i .d.); extraction time, 30 min; GC analysis conditions: 5 m x 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) nonanal, (2) decanal, (3) undecanal, and (4) dodecanal.

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214 Table 4.4 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak area reproducibility for a mixture of aldehydes extracted on a sol-gel PEG microextraction capillary. Name of Analyte GC Peak Area (arbitrary unit) Run #1Run #2 Run #3 Run #4 Run #5 RSD (%) Nonanal 5.5 5.7 5.8 5.2 5.5 4.1 Decanal 4.8 4.4 4.7 4.6 4.6 3.3 Undecanal 3.9 4.1 4.1 3.8 4.1 3.0 Dodecanal 3.2 2.9 3.1 3.0 2.9 3.4 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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215 Table 4.5 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary GC peak area re producibility for a mixture of aldehydes extracted on a solgel PEG microextraction capillary. Name of Analyte GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Nonanal 5.8 6.2 6.3 4.2 Decanal 4.4 4.6 4.7 3.5 Undecanal 4.1 4.0 4.3 3.9 Dodecanal 2.9 3.1 3.2 4.5 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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216 Table 4.6 Limits of detection (LOD) data fo r aldehydes in CME-GC-FID experiments using sol-gel PEG microe xtraction capillaries. Measured Noise (V) : 1.033 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Nonanal 100 15.3 20.4 Decanal 50 13.1 11.8 Undecanal 50 9.6 16.1 Dodecanal 100 6.6 46.9 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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217 Table 4.7 provides a list of 5 ketones that were extracted an d analyzed using sol-gel PEG coated capillaries. Figure 4.5 represents a gas chromat ogram of the mixture of 5 underivatized ketones extracted from an a queous solution. CME–GC–FID experiments using sol–gel PEG microextraction capillaries provided excellent ru n-to-run (Table 4.8) and capillary-to-capillary (Table 4.9) extr action repeatability characterized by RSD values under 5%. We were also able to achieve detection limits (e.g., 8.1 ng/L for valerophenone and 9.7 ng/L for hexanophenone by CME-GC-FID) significantly lower than those reported in the literat ure for the same compounds (e.g., 0.92 g/L for valerophenone and 0.33 g/L for hexanophenone, by CME-GC-FID) [23].

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218 Table 4.7 Chemical structures and pertinent phy sical properties of ketones extracted by CME using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound 4-Chloro acetophenone 154.59 20 232 1.192 O C l Valerophenone 162.23 -9 105 107 at 5 mm Hg 0.988 O Hexanophenone 176.26 25 26 265.1 0.958 O Benzophenone 182.22 48-49 305 1.11 O 2,3-Dichloro1,4naphthoquinone 227.05 193 275 at 2 mm Hg O O Cl Cl

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219 Figure 4.5 CME–GC analysis of ketones. Extr action conditions: sol–gel PEG coated microextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 4-chloroace tophenone, (2) valerophenone, (3) hexanophenone, (4) benzophenone, a nd (5) 2,3-dichloro-1,4-naphthoquinone.

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220 Table 4.8 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak area reproducibility for a mixtur e of ketones extracted on a sol-gel PEG microextraction capillary. Name of Analyte GC Peak Area (arbitrary unit) Run #1Run #2 Run #3 Run #4 Run #5 RSD (%) 4-Chloroacetophenone 5.8 5.9 5.9 5.8 6.2 2.9 Valerophenone 4.7 4.4 4.7 4.8 4.8 3.3 Hexanophenone 3.3 3.6 3.6 3.4 3.5 3.8 Benzophenone 5.3 5.1 5.6 5.7 5.4 4.1 2,3-Dichloro-1,4naphthoquinone 6.7 6.5 6.2 6.7 6.5 3.1 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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221 Table 4.9 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary GC peak area reproducibility for a mixture of ketones ex tracted on a sol-gel PEG microextraction capillary. Name of Analyte GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) 4-Chloroacetophenone 5.9 6.0 5.6 3.6 Valerophenone 4.4 4.6 4.8 4.9 Hexanophenone 3.6 3.8 3.5 4.4 Benzophenone 5.1 5.3 5.6 4.5 2,3-Dichloro-1,4-naphthoquinone 6.5 6.4 6.9 3.9 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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222 Table 4.10 Limits of detection (LOD) data fo r ketones in CME-GC-FID experiments using sol-gel PEG microe xtraction capillaries. Measured Noise (V) : 1.152 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) 4-Chloroacetophenone 500 14.4 119 Valerophenone 25 10.7 8.1 Hexanophenone 25 8.8 9.7 Benzophenone 25 11.9 7.2 2,3-Dichloro-1,4naphthoquinone 300 12.9 80.5 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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223 4.3.5.2 CME-GC-FID of Aromatic amines usin g sol-gel PEG coated microextraction capillaries Many aromatic amines are of industria l importance because of their use as intermediates in the synthesis of azo dyes, antioxidants in rubber products, and other commercial materials [33,34]. During producti on, use, and disposal of these goods, emissions of aromatic amines may occur. Epid emiological observations of the toxicity of aromatic amines were first reported in aniline dye factor ies by Rehn [35] in 1895, with the report that German and Swiss workers su ffered urinary bladder tumors [34]. A major toxicological issue is reaction with DNA and induction of carcinomas, primarily in the urinary bladder, liver, or other tissues in humans and experimental animals [36]. Many of these aromatic amines, have been classi fied as mutagenic and carcinogenic [37,38]. Therefore, accurate analysis of trace-level contents of aromatic amines in the environment and in drinking water is necessary. In our study, various aromatic amines were extracted from aqueous samples (Table 4.11). Figure 4.6 (a) and (b) repres ent gas chromatograms of a mixture of underivatized aromatic amines extracted from aqueous samples. As can be seen from Table 4.12 and Table 4.13 the run-to-run and cap illary-to-capillary relative standard deviation (RSD) values for GC peaks result ing from analytes extracted on sol-gel PEG coated capillaries were under 5%. We were able to obtain detection limits of 0.10 g/L and 0.39 g/L for N,N -dimethylaniline and 2,4-dimethylaniline, respectively (Table 4.14). These LODs were significantly lower compared to the reported literature values for the

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224 same compounds (1.06 g/L for N,N -dimethylaniline and 1.02 g/L for 2,4dimethylaniline) obtained in SPME-GC-FID experiments using 50 m thick polyaniline coatings with temperature and pH adjust ment of aqueous samples [39]. No such adjustments were needed in our CME-GC -FID experiments. Also, detection limit obtained for diphenyl amine (0.005 g/L) in our CME-GC-FID experiments was much lower than the reported literature values for the same compound (i.e. 5 g/L using PA coating and 0.5 g/L using commercial CW-DVB coating) in SPME-GC-FID experiments [40].

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225 Table 4.11 Chemical structures and pertinent phys ical properties of aromatic amines extracted by CME using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound N,N -dimethyl aniline 121.18 2.45 194 0.956 N 2,4-dimethyl aniline 121.18 16 218 0.98 NH2 Naphthyl amine 143.18 111.5 306.1 N H2 Acridine 179.22 107 346 N 2-chloroaniline 127.57 -1.94 208 1.213 Cl H2N 3-ethylaniline 121.18 -8 212 0.975 H2 N 3-bromoaniline 172.02 16.8 251 1.58 Br N H2 N -butylaniline 149.24 -12 241 0.931 NH Diphenyl amine 169.23 52 302 1.16 H N

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226 Figure 4.6-A CME–GC analysis of aromatic amin es. Extraction conditions: sol–gel PEG coated microextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) N,N-dimethylaniline, (2) 2,4dimethylaniline, (3) naphthylamine, and (4) acridine.

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227 Figure 4.6-B CME–GC analysis of aromatic amin es. Extraction conditions: sol–gel PEG coated microextraction capilla ry (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 2-chloroaniline, (2) 3-ethylaniline, (3) 3bromoaniline, (4) N-butylaniline, and (5) diphenylamine.

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228 Table 4.12 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak area reproducibility for a mixture of aromatic amines extracted on a sol-gel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) N,N -dimethylaniline 6.6 6.4 6.8 6.2 6.8 3.9 2,4-dimethylaniline 3.8 4.0 3.6 3.8 3.7 4.1 Naphthyl amine 3.7 3.9 4.1 3.6 3.9 4.9 Acridine 4.1 3.9 4.2 3.9 4.0 2.7 2-chloroaniline 3.5 3.7 3.6 3.4 3.6 3.3 3-ethylaniline 5.9 6.1 6.0 5.6 5.7 3.8 3-bromoaniline 4.7 4.3 4.4 4.8 4.5 4.4 N -butylaniline 6.8 6.4 6.9 6.5 6.7 2.9 Diphenyl amine 4.5 4.8 4.7 4.9 4.5 3.6 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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229 Table 4.13 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary GC peak area repr oducibility for a mixture of aromatic amines extracted on a sol-gel PEG microext raction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) N,N -dimethylaniline 6.8 6.8 7.4 4.6 2,4-dimethylaniline 3.6 3.7 4.0 4.8 Naphthyl amine 4.1 3.9 3.7 4.9 Acridine 4.2 4.0 4.4 4.3 2-chloroaniline 3.6 3.5 3.8 4.1 3-ethylaniline 6.1 5.8 6.2 4.2 3-bromoaniline 4.4 4.6 4.9 5.0 N -butylaniline 6.9 6.5 6.9 3.4 Diphenyl amine 4.7 4.9 5.1 4.2 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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230 Table 4.14 Limits of detection (LOD) data for aromatic amines in CME-GC-FID experiments using sol-gel PEG microextraction capillaries. Measured Noise (V) : 1.043 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) N,N -dimethylaniline 500 14.7 106 2,4-dimethylaniline 900 7.1 398 Naphthyl amine 250 7.9 98.5 Acridine 30 10.6 8.9 2-chloroaniline 900 10.0 281 3-ethylaniline 900 14.7 192 3-bromoaniline 900 7.8 363 N -butylaniline 35 12.8 8.6 Diphenyl amine 15 9.1 5.2 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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231 4.3.5.3 CME-GC-FID of phenol deriva tives using sol-gel PEG coated microextraction capillaries Phenols derivatives are produced as a resu lt of various processe s in pesticides-, dyes-, plastics-, paper-, and petrochemical industries [41-44]. Many of these phenol derivatives are often found in waters [45,46], soils [47], and sediments [47]. Because of their toxicity, US Environmental Protec tion Agency has classified 11 phenolic compounds as major pollutants [48]. Among the phenol derivatives extracte d, 2-tert-butyl-4-methoxyphenol (BHA) has been considered a possible carcinogen [ 49,50]. BHA is a chemical antioxidant used since 1947 as a preservative in some edible fa ts and oils, fat-contai ning or oil-containing foods such as baked goods and pork sausage, chewing gum, cosmetics, pharaceuticals, animal feed, food packaging, and in rubber and petroleum products. It prevents spoilage by reacting with oxygen, thus keeping the oxygen from reacting with fats and oils. It slows the development of off-flavors, odors and color changes caused by oxidation. In the present work, four phenol deriva tives were extracted using sol-gel PEG coated capillaries (Table 4.15). As can be seen from Figure 4.7, the sol-gel PEG coated capillaries were found to be effective in extracting four underiva tized phenols from an aqueous sample. Capillary microextraction re sults are presented in Table 4.16 and Table 4.17. The detection limits on the order of ng/L were obtained for aromatic amines in the CME–GC–FID experiments using sol–gel PEG co ated microextraction capillaries (Table 4.18). These values are better than the detection limits repor ted in the li terature. For

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232 instance, detection limits obtai ned for 2,4-dimethylphenol (0.07 g/L) and 2,4,6trichlorophenol (0.02 g/L) in our CME-GC-FID experi ments were lower than those reported in HS-SPME-GC-FID experiments for the same compounds using sol-gel DOHB15C5/OH-TSO coating (i.e 2,4-dimethylphenol (0.25 g/L) and 2,4,6-trichlorophenol (0.05 g/L)) [51] and using sol-gel PEG coating (i.e. 2,4-dimethylphenol (1.0 g/L) and 2,4,6-trichlorophenol (0.1 g/L)) [52].

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233 Table 4.15 Chemical structures and pertinent phys ical properties of phenol derivatives extracted by CME using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound 2,4dimethylphenol 122.17 27.5 210.9 0.965 OH 3,4dichlorophenol 163.0 67 145 146 Cl C l HO 2,4,6trichlorophenol 197.45 69.5 244.5 1.49 Cl C l Cl OH 2-tert-butyl-4methoxyphenol 180.25 57-62 OH O

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234 Figure 4.7 CME–GC analysis of phe nol derivatives. Extraction conditions: sol–gel PEG coated microextraction capilla ry (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 2,4-dimethylphenol, (2) 3,4dichlorophenol, (3) 2,4,6-tr ichlorophenol, and (4) 2-tert-butyl-4-methoxyphenol.

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235 Table 4.16 Experimental data on CME-GC replicat es measurements illustrating run-torun GC peak area reproducibility for a mixture of phenol derivatives extracted on a solgel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4 Run #5 RSD (%) 2,4-dimethylphenol 6.4 6.6 6.5 6.3 6.9 3.4 3,4-dichlorophenol 5.1 5.1 5.3 5.4 4.9 3.6 2,4,6-trichlorophenol 5.3 5.5 5.1 5.4 4.9 4.3 2-tert-butyl-4-methoxyphenol 6.7 6.9 7.1 6.9 6.9 2.6 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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236 Table 4.17 Experimental data on CME-GC replicates measurements illustrating capillary-to-capillary GC peak area reproducib ility for a mixture of phenol derivatives extracted on a sol-gel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) 2,4-dimethylphenol 6.5 6.9 6.8 3.4 3,4-dichlorophenol 5.3 5.9 5.8 4.5 2,4,6-trichlorophenol 5.1 5.3 5.6 4.9 2-tert-butyl-4-methoxyphenol 7.1 6.9 6.5 4.8 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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237 Table 4.18 Limits of detection (LOD) data fo r phenol derivatives in CME-GC-FID experiments using sol-gel PEG microextraction capillaries. Measured Noise (V) : 1.014 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) 2,4-dimethylphenol 300 13.0 70.3 3,4-dichlorophenol 500 9.6 159 2,4,6-trichlorophenol 80 10.4 23.3 2-tert-butyl-4methoxyphenol 170 11.8 43.7 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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238 4.3.5.4 CME-GC-FID of alcohols using so l-gel PEG coated microextraction capillaries In the present work, four alcohols we re extracted using sol-gel PEG coated capillaries (Table 4.19). Extraction of alc ohols from aqueous matrices often poses difficulty due to their high polar ity and pronounced affinity towa rd water. As can be seen from Figure 4.8, the sol-gel PEG capillaries were found to be effective in extracting underivatized alcohols from an aqueous sample without requiring any derivatization, pH adjustment or salting-out procedures. Run-to-run (Table 4.20) and capillary-to-capi llary (Table 4.21) peak area relative standard deviation (RSD) values for GC peak areas resulting from alcohols extracted on a sol-gel PEG coated capillaries were under 5% It demonstrates outstanding performance of the sol–gel PEG coating. We were also able to achieve detection limits of 0.02 g/L and 0.008 g/L for 1-octanol and 1-decanol, re spectively (Table 4.22). These LOD values were comparable to repo rted literature values of 0.01 g/L and 0.01 g/L for the same compounds obtained on sol-gel open chai n crown ether/OH-TSO coatings in HSSPME-GC-FID experiments with sample matr ix temperature and pH adjustments [53].

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239 Table 4.19 Chemical structures and pertinent phys ical properties of alcohols extracted by CME using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound 1-heptanol 116.20 -36 176 0.823 OH 1-octanol 130.23 -15 195 0.826 OH 1-nonanol 144.26 -8 to -6 215 0.828 OH 1-decanol 158.28 6 230 0.829 OH

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240 Figure 4.8 CME–GC analysis of alcohols. Extraction conditions: sol–gel PEG coated microextraction capillary (12 cm x 250 m i .d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 1-heptanol, (2) 1-octanol, (3) 1-nonanol, and (4) 1-decanol.

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241 Table 4.20 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak area reproducibility for a mixtur e of alcohols extracted on a sol-gel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) 1-heptanol 7.7 7.5 7.9 7.8 7.6 2.5 1-octanol 6.6 6.7 6.2 6.0 6.4 4.2 1-nonanol 6.5 6.1 6.2 6.0 6.4 3.1 1-decanol 3.9 4.0 3.9 3.7 4.1 3.9 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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242 Table 4.21 Experimental data on CME-GC replicates measurements illustrating capillary-to-capillary GC peak area reproducibility for a mixture of alcohols extracted on a sol-gel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) 1-heptanol 7.9 8.2 7.7 3.2 1-octanol 6.2 6.4 6.8 4.7 1-nonanol 6.2 6.3 6.9 3.5 1-decanol 3.9 3.9 3.6 4.9 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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243 Table 4.22 Limits of detection (LOD) data for alcohols in CME-GC-FID experiments using sol-gel PEG microe xtraction capillaries. Measured Noise (V) : 1.030 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) 1-heptanol 700 16.2 134 1-octanol 100 13.8 22.4 1-nonanol 40 13.3 9.3 1-decanol 20 7.6 8.1 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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244 4.3.5.5 CME-GC-FID of free fatty acids usin g sol-gel PEG coated microextraction capillaries Free fatty acids are the key metabolites and intermediates in biological processes [54]. Fatty acids have also received considerable attention in the scientific as well as popular press because of its linkage to several chronic diseases, such as insulin resistance [55,56], coronary artery diseas e [57] and certain types of cancer [58,59]. Hence, the determination of these fatty acids in various matrices such as blood plasma and urine is of great importance. The hydrophilic nature of fatty acids makes their extraction from aqueous matrices an extremel y difficult analytical task. Table 4.23 lists the free fatty acids th at were extracted using sol-gel PEG microextraction capillaries. Sol-gel PEG co ated capillaries were able to efficiently extract underivatized free fatty acids from aqueous samples wi thout requiring any derivatization, pH adjustment or salting-out procedures. A typical gas chromatogram obtained from these experiments is shown in Fi gure 4.9. It must be no ted that this was the first time a small molecular weight PEG was successfully used to extract free fatty acids without any modification to the analytes or the sa mple matrix. CME–GC–FID experiments using sol–gel PEG microextracti on capillaries provided excellent run-to-run (Table 4.24) and capillary-to-capillary (Table 4.25) extraction repeat ability characterized by RSD values of less than 4% and 5%, resp ectively. We were also able to achieve detection limits (e.g., 0.07 g/L for octanoic acid and 0.02 g/L for decanoic acid, by CME-GC-FID) comparable to those reported in the literature usi ng sol-gel open chain

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245 crown ether/OH-TSO coated SPME fiber (e.g., 0.03 g/L for octanoic acid and 0.03 g/L for decanoic acid, by SPME-GC-FID) [53] and using in situ derivatization of fatty acids on polyacrylate coated SPME fiber (e.g., 0.04 g/L for octanoic acid and 0.02 g/L for decanoic acid, by SPME-GC-FID) [60]. LOD resu lts for the fatty acids are provided in Table 4.26.

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246 Table 4.23 Chemical structures and pertinent phys ical properties of free fatty acids extracted by using sol-gel PEG coating. Name of Compound Molecular Weight (g/mol) Melting Point ( C) Boiling Point ( C) Density (g/mL) Structure of Compound Octanoic acid 144.21 16 237 0.911 O OH Nonanoic acid 158.24 9 254 0.906 O OH Decanoic acid 172.27 31 32 268 270 0.901 O OH Undecanoic acid 186.29 28 31 228 at 160 mm Hg O OH

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247 Figure 4.9 CME–GC analysis of free fatty aci ds. Extraction condi tions: sol–gel PEG coated microextraction capilla ry (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) octanoic acid, (2) nonanoic acid, (3) decanoic acid, and (4) undecanoic acid.

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248 Table 4.24 Experimental data on CME-GC replicate measurements illustrating run-to-run GC peak area reproducibility for a mixture of free fatty acids extracted on a sol-gel PEG microextraction capillary. Name of Analytes GC Peak Area (arbitrary unit) Run #1Run #2Run #3Run #4Run #5 RSD (%) Octanoic acid 10.3 10.5 10.3 10.0 9.8 2.5 Nonanoic acid 7.2 7.5 7.4 7.0 6.8 3.7 Decanoic acid 7.4 7.5 7.7 7.5 7.3 2.2 Undecanoic acid 11.0 10.5 10.9 10.7 10.9 1.9 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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249 Table 4.25 Experimental data on CME-GC replicate measurements illustrating capillaryto-capillary GC peak area re producibility for a mixture of free fatty acids extracted on a sol-gel PEG microext raction capillary. Name of Analytes GC Peak Area (arbitrary unit) Capillar y #1 Capillary #2 Capillary #3 RSD (%) Octanoic acid 10.3 10.6 9.9 3.1 Nonanoic acid 7.4 7.7 7.0 4.6 Decanoic acid 7.7 8.4 8.0 4.3 Undecanoic acid 10.9 10.7 11.4 3.7 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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250 Table 4.26 Limits of detection (LOD) data for free fatty acids in CME-GC-FID experiments using sol-gel PEG microextraction capillaries. Measured Noise (V) : 1.012 Name of analyte Concentration ( g/L) Measured peak height (mV) Limit of detection (ng/L), (S/N = 3) Octanoic acid 400 17.9 67.8 Nonanoic acid 140 13.7 31.1 Decanoic acid 100 15.3 19.7 Undecanoic acid 150 17.9 25.5 Extraction conditions: sol–gel PEG coated mi croextraction capillary (12 cm x 250 m i.d.); extraction time, 30 min; GC analysis conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; in jector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 20 oC/min; helium carrier gas; FID temperature 350 oC.

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251 4.3.5.6 CME-GC-FID of mixture of moderate ly polar and highly polar compounds using sol-gel PEG coated microextraction capillary A mixture containing analytes from different chemical classes representing a wide polarity range was extracted from an aqueous sample using a sol-gel PEG coated capillary. As is revealed from the chroma togram (Figure 4.10), a sol-gel PEG coated capillary can be effectively used to simulta neously extract moderately polar, and highly polar compounds from an aqueous matrix. 4.3.5.7 CME performance of sol-gel capillari es prepared with and without TESP Finally, the extraction performance of sol-gel PEG capillary was compared to a capillary coated without TESP (sol-gel co-precursor with a bonded PEG moiety). Figures 4.11 and 4.12 compares the extraction of an aqueous sample contai ning two alcohols and two free fatty acids obtained on two sol-gel co ated microextraction capillaries: a sol-gel PEG capillary [Figure 4.11] and a capillary coated withou t TESP [Figure 4.12]. It is evident from these figures that in the abse nce of polar PEG moieties, the methyl groups (from MTMOS precursor) cannot compete with water to provide extraction of highly polar analytes like free fa tty acids and alcohols.

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252 Figure 4.10 CME–GC analysis of a mi xture of moderately polar and highly polar organic compounds. Extraction conditions: sol–gel PEG co ated extraction capi llary (12 cm 250 m i.d.). extraction time, 30 min., GC analys is conditions: 5 m 250 m i.d. sol–gel PDMS column; splitless injection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5 min) to 320 oC at a rate of 15 oC/min; helium carrier gas; FID temperature 350 oC. Peaks: (1) 1-octanol, (2) 2,4-dimethylphenol, (3) decanal, (4) N-butylaniline, and (5) heptanophenone.

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253 Figure 4.11 CME–GC analysis of mixture of two alcohols and two free fatty acids extracted on a sol-gel microextraction capilla ry (12 cm x 250 m i.d.) prepared by using TESP in the coating sol solution; Extraction time, 30 min; GC anal ysis conditions: 5 m x 250 m i.d. sol–gel PDMS column; splitless inj ection; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temper ature programmed from 35 oC (5 min) to 320 oC at a rate of 15 oC/min; helium carrier ga s; FID temperature 350 oC. Peaks: (1) 1-heptanol, (2) 1-octa nol, (3) octanoic aci d, (4) nonanoic acid.

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254 Figure 4.12 CME–GC analysis of mixture of two alcohols and two free fatty acids on a sol-gel coated microextraction capillary (12 cm x 250 m i.d.) prepared without TESP in the coating sol solution; Extr action time, 30 min; GC anal ysis conditions: 5 m x 250 m i.d. sol–gel PDMS column; splitless injec tion; injector temperature: initial 30 oC, final 340 oC, programmed at a rate of 60 oC/min; GC oven temperature programmed from 35 oC (5min) to 320 oC at a rate of 15 oC/min; helium carrier gas; FID temperature 350 oC.

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255 4.4 Conclusion For the first time, low molecular weight PE G was used to prepare sol-gel coatings for capillary microextraction. The used sol-ge l PEG coated microextraction capillaries were very effective in preconcentration and tr ace analysis of modera tely polar and highly polar compounds. Using sol-gel PEG coated mi croextraction capillaries, low ng/L level detection limits were achieved for both mode rately polar and highly polar analytes directly extracted from aque ous media without requiring deri vatization, pH adjustment, or salting out procedures. The sol-gel PEG mi croextraction coatings showed remarkable performance repeatability evident from their run-to-run and capillary -to-capillary peak area RSD values of lower than 5%. Since lo w molecular weight sol–gel PEG extraction phase shows excellent thermal (340 C) and solvent stability, the sol–gel PEG coatings are suitable for coupling with both GC and HPLC.

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256 4.5 References to chapter 4 [1] J.A. Yancey, J. Chromatogr. 23 (1985) 161. [2] P. Sandra, F. David, M. Proot, G. Diri cks, M. Verstappe, M. Verzele, J. High Resolut. Chromatogr. Chromatogr. Commun. 8 (1985) 782. [3] W.R. Supina, L.R. Rose, J. Chromatogr. Sci. 8 (1970) 214. [4] L. Rohrschneider, Advances in Ch romatography, Marcel Dekker, New York, 1967. [5] B.J. Hall, J.S. Brodbelt, J. Chromatogr. A 777 (1997) 275. [6] V. Mani, Applications of Solid Ph ase Microextraction, Royal Society of Chemistry, Cambridge, UK, 1999. [7] M. Ciganek, M. Dressler, J. Teply, J. Chroma togr. 588 (1991) 225. [8] J. de Zeeuw, J. Luong, TrAc, Trends Anal. Chem. 21 (2002) 594. [9] M. Horka, V. Kahle, K. Janak, K. Tesarik, J. High. Resolut. Chromatogr. Chromatogr. Commun. 8 (1985) 259. [10] M. Horka, V. Kahle, K. Janak, K. Tesarik, Chromatographia 21 (1986) 454. [11] L. Bystricky, J. High. Resolut. Chromatogr. Chromatogr. Commun. 9 (1986) 240. [12] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [13] R.G.d.C. Silva, F. Augusto, J. Chromatogr. A 1072 (2005) 7–12. [14] M. Cai, W. Wang, J. Xing, Y. Fe ng, C. Wu, Fenxi Huaxue 34 (2006) 91. [15] S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Alli, A. Malik, Anal. Chem. 74 (2002) 752. [16] C. Shende, A. Kabir, E. Townsend, A. Malik, Anal. Chem. 75 (2003) 3518. [17] D. Wang, S.L. Chong, A. Ma lik, Anal. Chem. 69 (1997) 4566. [18] S.L. Chong, D. Wang, J.D. Hayes, B.W. Wilhite, A. Malik, Anal. Chem. 69 (1997) 3889.

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257 [19] J.D. Hayes, A. Malik, J. Chromatogr. B 695 (1997) 3. [20] A. Kabir, in "Polytetrahydrofuran-a nd Dendrimer-Based Novel Sol-Gel Coatings for Capillary Microextraction (CME) Provi ding Parts Per Trillion (ppt) and Parts Per Quadrillion (ppq) Level Detectio n Limits in Conjunction With Gas Chromatography and Flame Ionization Det ection (FID)", Univ ersity of South Florida, Tampa, 2005, p. 299. [21] Z. Zeng, W. Qiu, Z. Hu ang, Anal. Chem. 73 (2001) 2429. [22] A. Malik, S.L. Chong, Applications of Solid Phase microextraction, Royal Society of Chemistry, Cambridge, UK, 1999. [23] K. Alhooshani, T.-Y. Kim, A. Kabir, A. Malik, J. Chromatogr. A 1062 (2005) 1. [24] T.Y. Kim, K. Alhooshani, A. Kabir, D.P. Fries, A. Mali k, J. Chromatogr. A 1047 (2004) 165. [25] A. Kabir, C. Hamlet, K.S. Yoo, G.R. Newkome, A. Malik, J. Chromatogr. A 1034 (2004) 1. [26] S. Kulkarni, L. Fang, K. Alhooshani A. Malik, J. Chro matogr. A 1124 (2006) 205–216. [27] C. Brinker, G. Schere r, Sol–Gel Science. The Physics and Chemistry of Sol–Gel Processing, Academic Press, San Diego, CA, 1990. [28] R.J. Kieber, K. Mopper, E nviron. Sci. Technol. 24 (1990) 1477. [29] M.L. Bao, F. Pantani, O. Griffini, D. Burrini, D. Santianni, K. Barbieri, J. Chromatogr. A 809 (1998) 75. [30] G.D. Leikauf, Environmental Toxi cants:Human Exposures and Their Health Effects, Van Nostrand Reinhold, New York, 1992. [31] N.R. Council, Formaldehyde and Ot her Aldehydes: Board on Toxicology and Environmental Health Hazards, Nationa l Academy Press, Washington, DC, 1981. [32] J. Nawrocki, J. Chromatogr. A 749 (1996) 157. [33] J.L. Radomski, Annu. Rev. Pharmacol. 19 (1979) 129–157. [34] R.C. Garner, C.N. Martin, D.B. Clayson, Chemical Carcinogens, Amer. Chem. Soc., Washington, DC, 1984.

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258 [35] L. Rehn, Archiv. Clin. Chirgurie 50 (1895) 588–600. [36] D. Kim, F.P. Guengerich, Ann. Rev. Pharmacol. Toxicol. 45 (2005) 27. [37] ACGIH, Threshold Limit Values and Biological Exposure Indices, ACGIH-Press, Cincinnati, OH, 1999. [38] D.-D. Forschungsgemeinschaft, MAKand BATValues, VCH, Weinheim, 2000. [39] M. Huang, T. Chao, Q. Zhou, G. Jiang, J. Chromatogr. A 1048 (2004) 257. [40] H. Van Doom, C.B. Grabanski, D.J. Miller, S.B. Hawthorne, J. Chromatogr. A 829 (1998) 223. [41] M. Molder, S. Schrader, U. Franc k, P. Popp, Fresen., J. Anal. Chem. 357 (1997) 326. [42] E. Gonzalez-Toledo, M.D. Part, M.F. Alpendurada, J. Chromatogr. A 923 (2001) 45. [43] A. Penalver, E. Pocurull, F. Borrull R.M. Marce, J. Chromatogr. A 953 (2002) 79. [44] K.J. James, M.A. Stack, Fres en, J. Anal. Chem. 358 (1997) 833. [45] D. Puig, D. Barcelo, Tr ends Anal. Chem. 15 (1996) 362. [46] M. Llompart, M. Lourido, P. Land n, C. Garc a-Jares, R. Cela, J. Chromatogr. A 963 (2002) 137. [47] M.R. Lee, Y.C. Yeh, W.S. Hsia ng, B.H. Hwang, J. Chromatogr. A 806 (1998) 317. [48] US, Environmental, Protection, Agen cy, in, EPA method 625 Fed. Reg., part VIII, 40 CFR part 136, 1981, p. 58. [49] N. Ito, S. Fukushima, A. Hagiwara, M. Shibata, T. Ogiso, J. Natl Cancer Inst. 70 (1983) 343–352. [50] IARC, Monographs on the Evaluation of the Carcinogenic Risks of Chemicals to Humans 40 (1986) 123. [51] D. Wang, J. Xing, J. Peng, C. Wu, J. Chromatogr. A 1005 (2003) 1.

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259 [52] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [53] M. Liu, Z. Zeng, Y. Lei, H. Li, J. Sep. Sci. 28 (2005) 2306. [54] E. Fogelqvist, B. Josefsson, C. Roos J. High Resolut. Chromatogr. Chromatogr. Commun. 3 (1980) 568. [55] L.H. Storlien, E.W. Kraegen, D.J. Chisholm, Science 237 (1987) 885. [56] J. Yang, G.W. Xu, Q.F. H ong, J. Chromatogr. B 813 (2004) 53. [57] P. Franck, M. Jean, D. Marie, Int. J. Cardiol. 78 (2001) 27. [58] Y. Xu, Z. Shen, D. Wiper, J. Am. Med. Assoc. 280 (1998) 719. [59] J.D. Potter, J. Am. Med. Assoc. 268 (1992) 1573. [60] L. Pan, M. Adams, J. Pawliszyn, Anal. Chem. 67 (1995) 4396.

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260 APPENDICES

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261 Appendix A

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262 Appendix A (Continued)

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273 Appendix B Quantitative Analysis in CME In CME, first experiment s should be performed to determine extraction time profile of target analyte(s) (i.e., minimum ti me required for the extraction of equilibrium concentration of target analyte(s) from the sample matrix) since the extraction process is based on distribution of target analyte(s) between extracting phase (coating) and sample matrix. The initial experiments give an estim ate about the effectiven ess of a CME coating in extracting target analyte(s) from sample matrix, and indicate if there is a need for further optimization of experimental parame ter(s) (e.g., sample flow rate, temperature, pH, salt concentration, etc.). It also gives a good estimate of the detection limits that are to be expected. The choice of the quantitation method depends primarily on the nature of sample matrix. Simple matrices (e.g., drinking water) ususally do not have interferences that might hinder the equilibrium extr action of target analyte(s). Th erefore, a calibration curve prepared using known concentration of target analyte(s) can be used for quantitative analyses of analyte(s) of unknown concentrat ion. Based on the principles of SPME (or CME) [1], the amount of analyte(s) extrac ted from the sample at equilibrium (and under set conditions like sample temperature, pH, and salt concentration) will be directly proportional to the initial concen tration of the analyt e(s) in the sample Therefore, it is obvious that a linear calibration curve can be obtained (Figure B-1). The concentrations

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274 Appendix B (Continued) used to prepare linear calibration curve must cover the concentration range of the target analyte(s). After extraction, the analytical response fo r the unknown sample can be measure and, using the calibration curve (equatio n of line, y = mx + b), the analyst can interpolate to find the unknown concentration of analyte(s) in the sample. In case of complex matrices (e.g., river wa ter, waste water, etc.), some of the matrix components (e.g., suspended matter) ar e likely to interfere with the extraction process or modify the properties of the coa ting (e.g., surfactants). Th erefore, a standard addition method is recommended for quantitativ e analyses of target analyte(s) of unknown concentration. In this method, the sample containing unknown concentration of target analyte(s) is divided into several portio ns. A series of samples are then prepared by adding known amount (concentration) of an anal yte (a standard) to th e sample containing unknown concentration of target analyte(s). Af ter equilibrium extraction by CME, each of these samples can then be analyzed. Since the analytical response will be directly proportional to the analyte concen tration, a standard addition curve can be prepared and the analyst can extrapolate to find the unknown concentration of analyte(s) in the sample (Figure B-2). In practice, a small volume of concentrated standard is added to avoid significant changes in the sample matrix composition.

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275 Appendix B (Continued) Figure B-1 Calibration curve for target analyte of known concentration. Analytical Signal Concentration 0 1 2 3 4567 8 y = mx + b

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276 Appendix B (Continued) Figure B-2 Standard addition curve for target analyte Reading obtained with added standard Reading of unknown without added standard Concentration Concentration of Unknown 01234 5 6 7 1 2 3 4 5 Analytical Signal

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277 Appendix B (Continued) Reference: [1] J. Pawliszyn, Solid Phase Microextr action: Theory and Practice, Wiley-VCH, New York, 1997, p. 15.

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278 Appendix C Optimization of Sol-gel Coating Solution Composition An important step in the preparation of a sol-gel coating for both fiber SPME and CME is the optimization of the sol soluti on composition. The successf ul creation of the desired sol-gel sorbent depe nds upon proper selection a nd optimization of relative proportions of the sol solution ingredients. Th e sol solution ingredie nts typically include sol-gel precursor(s), a solven t system, a catalyst, water, and a sol-gel active organic ligand/polymer. In our work, concentration of sol-gel precursor(s) and solgel active organic ligand/polymer was chosen in a way that give s polarity to the CME coating necessary for effective extraction of polar as well as nonpolar analytes fr om aqueous matrix. Since the total amount of sol solution used to prepare CME coatings was less than 1 mL the amount of sol-gel active components (i.e. sol-ge l precursor(s) and sol-gel active organic ligand/polymer), containing orga nic groups or side chains (responsible for the extraction of organic analyte(s) from a queous matrix), used were limited to 50 mg or less. Increase in the amount of any one of the components (i.e. sol-gel precurso r(s) or sol-gel active organic polymer) led to increase in the amount of catalyst and solvent required to achieve a reasonable gelation time (~ 1 – 2 h). During the optimization of sol-gel process, catalyst (trifluoroacetic acid (TFA)) with low concentrations of water (usually 5-10 %) served as a controlled source of water fo r the sol-gel hydrolys is reaction. Keepi ng the amount of

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279 Appendix C (Continued) sol-gel precursor(s) and sol-gel active orga nic polymer constant, catalyst and solvent amounts were varied to achieve a gelation time of ~ 1 h. The 1 h gelation is necessary to give an analyst enough time to insert a vial containing sol soluti on into the capillary filling/purging device, fill th e capillary under helium gas flow, allow enough time (15 30 min) for the growing sol-ge l network to form chemical bonds with the fused silica capillary inner wall, and purge the excess unreacted sol solution before the gel fills the entire volume of the capillary blocking it. Figure C-1 demons trates the progress of sol-gel reaction. Figure C-1 Progress of sol-gel reactions: (A) just after addition of all the sol-gel ingredients (i.e. precursors, polymer, catalyst containing water, and solvent); (B) after 35 minutes; (C) after 1 hour. (A) (B) (C)

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280 Appendix D Limit of Detection Data for Various Organ ic Analytes Extrac ted using Sol-gel CNPDMS, Short Chain Sol-gel PEG, and Oth er SPME/CME Coatings reported in the Literature Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 2.9 Sol-gel CN-PDMS Chapter 3 3.6 Sol-gel dendrimer [1] 0.6 Sol-gel polyTHF [2] Acenaphthene 160 Sol-gel zirconia PDMDPS [3] 3.0 Sol-gel CN-PDMS Chapter 3 2.3 Sol-gel dendrimer [1] 0.5 Sol-gel polyTHF [2] 90 Sol-gel zirconia PDMDPS [3] 0.4 Sol-gel PDMS [4] Fluorene 5.6 Sol-gel C(4)-OH-TSO [5] 3.1 Sol-gel CN-PDMS Chapter 3 2.1 Sol-gel dendrimer [1] 0.4 Sol-gel polyTHF [2] 60 Sol-gel zirconia PDMDPS [3] 0.9 Sol-gel PDMS [4] Phenanthrene 8.0 sol-gel C(4)-OH-TSO [5] 4.1 Sol-gel CN-PDMS Chapter 3 2.2 Sol-gel dendrimer [1] 0.3 Sol-gel polyTHF [2] 0.4 Sol-gel PDMS [4] PAHs Fluoranthene 250 Commercial PDMS [6] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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281 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 16.8 Sol-gel CN-PDMS Chapter 3 20.4 Sol-gel PEG Chapter 4 19.4 Sol-gel dendrimer [1] 1.0 Sol-gel polyTHF [2] 330 Sol-gel zirconia PDMDPS [3] Nonanal 40.4 Sol-gel PDMS [4] 11.8 Sol-gel PEG Chapter 4 3.3 Sol-gel dendrimer [1] 0.6 Sol-gel polyTHF [2] 80 Sol-gel zirconia PDMDPS [3] Decanal 28.4 Sol-gel PDMS [4] 16.1 Sol-gel PEG Chapter 4 3.5 Sol-gel dendrimer [1] 0.8 Sol-gel polyTHF [2] 100 Sol-gel zirconia PDMDPS [3] Undecanal 50.5 Sol-gel PDMS [4] 12.0 Sol-gel CN-PDMS Chapter 3 46.9 Sol-gel PEG Chapter 4 0.9 Sol-gel polyTHF [2] Aldehydes Dodecanal 50 Sol-gel zirconia PDMDPS [3] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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282 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 7.0 Sol-gel CN-PDMS Chapter 3 44.3 Sol-gel dendrimer [1] Butyrophenone 1.0 Sol-gel polyTHF [2] 2.7 Sol-gel CN-PDMS Chapter 3 8.1 Sol-gel PEG Chapter 4 11.7 Sol-gel dendrimer [1] 0.5 Sol-gel polyTHF [2] 920 Sol-gel zirconia PDMDPS [3] Valerophenone 215 Sol-gel PDMS [4] 2.3 Sol-gel CN-PDMS Chapter 3 9.7 Sol-gel PEG Chapter 4 3.7 Sol-gel dendrimer [1] 0.6 Sol-gel polyTHF [2] 330 Sol-gel zirconia PDMDPS [3] Hexanophenone 109 Sol-gel PDMS [4] 3.4 Sol-gel CN-PDMS Chapter 3 7.2 Sol-gel PEG Chapter 4 Benzophenone 15.2 Sol-gel dendrimer [1] 4.7 Sol-gel CN-PDMS Chapter 3 Ketones Anthraquinone 32.7 Sol-gel PDMS [4] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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283 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 115 Sol-gel CN-PDMS Chapter 3 106 Sol-gel PEG Chapter 4 1200 Sol-gel PDMS/ CD [7] N,N -Dimethylaniline 1060 Polyaniline [8] 35.9 Sol-gel CN-PDMS Chapter 3 Benzanilide 5.9 Sol-gel PEG [4] 398 Sol-gel PEG Chapter 4 66.8 Sol-gel C(4)-OHTSO [5] 4.3 Sol-gel diglycidyloxy C(4)OH-TSO [9] 380 Sol-gel titania-OHTSO [10] 2,4-dimethylaniline 1020 Polyaniline [8] 5.2 Sol-gel PEG Chapter 4 5000 Polyacrylate [11] Diphenyl amine 500 CW-PDVB [11] 98.5 Sol-gel PEG Chapter 4 Aromatic amines Naphthyl amine 11 PDMS/PDVB [12] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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284 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 70.3 Sol-gel PEG Chapter 4 600 Sol-gel C(4)-crown-OHTSO [13] 1300 Polyaniline [14] 250 Sol-gel B15C5/OH-TSO [15] 2,4Dimethylphenol 1000 Sol-gel PEG [16] 137 Sol-gel CN-PDMS Chapter 3 85 Sol-gel polyTHF [2] 200 Sol-gel C(4)-crown-OHTSO [13] 100 Sol-gel B15C5/OH-TSO [15] 100 Sol-gel PEG [16] 2,4dichlorophenol 3700 Polyaniline [17] 161 Sol-gel CN-PDMS Chapter 3 23.3 Sol-gel PEG Chapter 4 220 Sol-gel dendrimer [1] 81 Sol-gel polyTHF [2] 1300 Polyaniline [17] 50 Sol-gel B15C5/OH-TSO [15] 2,4,6trichlorophenol 100 Sol-gel PEG [16] 56.9 Sol-gel CN-PDMS Chapter 3 260 Sol-gel dendrimer [1] 4-chloro-3methyl phenol 30 Sol-gel polyTHF [2] 39.1 Sol-gel CN-PDMS Chapter 3 18 Sol-gel polyTHF [2] 690 Polyaniline [17] 5000 Polyacrylate [11] Phenols Pentachloro phenol 20000 CW-PDVB [11] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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285 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 60.3 Sol-gel CN-PDMS Chapter 3 134 Sol-gel PEG Chapter 4 13 Sol-gel polyTHF [2] 1-Heptanol 20 Sol-gel C(4)-crownOH-TSO [13] 4.3 Sol-gel CN-PDMS Chapter 3 22.4 Sol-gel PEG Chapter 4 11.2 Sol-gel dendrimer [1] 5.0 Sol-gel polyTHF [2] 1-Octanol 10 Sol-gel C(4)-crownOH-TSO [13] 1.6 Sol-gel CN-PDMS Chapter 3 9.3 Sol-gel PEG Chapter 4 2.3 Sol-gel dendrimer [1] 1-Nonanol 0.7 Sol-gel polyTHF [2] 1.4 Sol-gel CN-PDMS Chapter 3 8.1 Sol-gel PEG Chapter 4 1.0 Sol-gel dendrimer [1] 0.6 Sol-gel polyTHF [2] Alcohols 1-Decanol 10 Sol-gel C(4)-crownOH-TSO [13] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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286 Appendix D (continued) Chemical class of analyte Name of analyte Detection limits (ng/L) SPME/CME Coating References 197 Sol-gel CN-PDMS Chapter 3 523 Sol-gel OH-TSO-BMADVB [18] 270 Sol-gel TMSPMA-OHTSO [19] 400 Sol-gel C(4)-crown-OHTSO [13] Hexanoic acid 500 Polyacrylate [20] 67.8 Sol-gel PEG Chapter 4 91.5 Sol-gel OH-TSO-BMADVB [18] 20 Sol-gel TMSPMA-OHTSO [19] 30 Sol-gel C(4)-crown-OHTSO [13] Octanoic acid 40 Polyacrylate [20] 38.7 Sol-gel CN-PDMS Chapter 3 31.1 Sol-gel PEG Chapter 4 Nonanoic acid 30 Polyacrylate [20] 13.4 Sol-gel CN-PDMS Chapter 3 19.7 Sol-gel PEG Chapter 4 50.4 Sol-gel OH-TSO-BMADVB [18] 10 Sol-gel TMSPMA-OHTSO [19] 30 Sol-gel C(4)-crown-OHTSO [13] Free fatty acids Decanoic acid 20 Polyacrylate [20] S. Kulkarni, L. Fang, K. Alhooshani, A. Malik, J. Chromatogr. A 1124 (2006) 205.

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287 Appendix D (continued) References: [1] A. Kabir, C. Hamlet, K.S. Yoo, G.R. Newkome, A. Malik, J. Chromatogr. A 1034 (2004) 1. [2] A. Kabir, C. Hamlet, A. Malik, J. Chromatogr. A 1047 (2004) 1. [3] K. Alhooshani, T.-Y. Kim, A. Kabir, A. Malik, J. Chromatogr. A 1062 (2005) 1. [4] S. Bigham, J. Medlar, A. Kabir, C. Shende, A. Alli, A. Malik, Anal. Chem. 74 (2002) 752. [5] X. Li, Z. Zeng, S. Gao, H. Li, J. Chromatogr. A 1023 (2004) 15. [6] R.A. Doong, S.M. Chang, Y.C. Sun, J. Chromatogr. A 879 (2000) 177. [7] Y.-l. Fu, Y.-l. Hu, Y.-j. Zheng, G.-K. Li, J. Sep. Sci. 29 (2006) 2684. [8] M. Huang, T. Chao, Q. Zhou, G. Jiang, J. Chromatogr. A 1048 (2004) 257. [9] X. Li, S. Gong, Z. Zeng, Chromatographia 62 (2005) 519. [10] X. Li, J. Gao, Z. Zeng, Anal. Chim. Acta 590 (2007) 26. [11] H. Van Doom, C.B. Grabanski, D.J. Miller, S.B. Hawthorne, J. Chromatogr. A 829 (1998) 223. [12] T. Zimmermann, W.J. Ensinger, T.C. Schmidt, Anal. Chem. 76 (2004) 1028. [13] M. Liu, Z. Zeng, Y. Lei, H. Li, J. Sep. Sci. 28 (2005) 2306. [14] M. Mousavi, E. Noroozian, M. Jalali-H eravi, A. Mollahosseini, Anal. Chim. Acta. 581 (2007) 71. [15] D. Wang, J. Xing, J. Peng, C. Wu, J. Chromatogr. A 1005 (2003) 1. [16] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [17] H. Bagheri, A. Mir, E. Babanezhad, Anal. Chim. Acta 532 (2005) 89.

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288 [18] M. Liu, Z. Zeng, Y. Tian, Anal. Chim. Acta 540 (2005) 341. [19] M. Liu, Z. Zeng, B. Xiong, J. Chromatogr. A 1065 (2005) 287. [20] L. Pan, M. Adams, J. Pawliszyn, Anal. Chem. 67 (1995) 4396.

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ABOUT THE AUTHOR Sameer M. Kulkarni was born in Mumb ai (Bombay), India. He received a Bachelor of Science degree in Chemistry from University of Mumbai in 1999. He continued his studies at the same University and received Master of Science degree in Inorganic Chemistry in 2001. Later, he came to United States and joined the Department of Chemistry, Eastern Michigan University, as a Master’s student. However, later, he decided to transfer to University of Sout h Florida to pursue a Doctorate Degree in Analytical Chemistry. He joined Dr. Abdul Malik’s research group in 2002 and worked on developing polar sol-gel coatings for cap illary microextraction. He has 1 publication and 2 manuscripts submitted to international journals.