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Germania-based sol-gel organic-inorganic hybrid coatings for capillary microextraction

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Title:
Germania-based sol-gel organic-inorganic hybrid coatings for capillary microextraction
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English
Creator:
Fang, Li
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University of South Florida
Place of Publication:
Tampa, Fla.
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Subjects / Keywords:
Sol-gel germania coating
CME
SPME
In-tube SPME
Gas chromatography
Stationary phase
Dissertations, Academic -- Chemistry -- Doctoral -- USF   ( lcsh )
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bibliography   ( marcgt )
non-fiction   ( marcgt )

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Summary:
ABSTRACT: For the first time, germania-based hybrid organic-inorganic sol-gel materials were developed for analytical sample preparation and chromatographic separation. Being an isostructural analog of silica (SiO₂), germania (GeO₂) is compatible with silica network. This structural similarity, which is reflected by the relative positions of germanium and silicon in the periodic table, stimulated our investigation on the development of germania-based sol-gel hybrid organic-inorganic coatings for analytical applications. Sol-gel sorbents and stationary phases reported to date are predominantly silica-based. Poor pH stability of silica-based materials is a major drawback. In this work, this problem was addressed through development of germania-based organic-inorganic hybrid sol-gel materials.For this, tetramethoxygermane (TMOG) and tetraethyoxygermane (TEOG) were used as precursors to create a sol-gel network via hydrolytic polycondensation reactions to provide the inorganic component (germania) of the organic-inorganic hybrid coating. The growing sol-gel germania network was simultaneously reacted with an organic ligand that contained sol-gel-active sites in its chemical structure. Hydroxy-terminated polydimethylsiloxane (PDMS) and 3-cyanopropyltriethoxysilane (CPTES) served as sources of nonpolar and polar organic components, respectively. The sol-gel reactions were performed within fused silica capillaries. The prepared sol-gel germania coatings were found to provide excellent pH and thermal stability. Their extraction characteristics remained practically unchanged after continuous rinsing of the sol-gel germania-PDMS capillary for 24 hours with highly basic (pH=13) and/or acidic (pH = 1.3) solution.They were very efficient in extracting non-polar and moderately polar analytes such as polycyclic aromatic hydrocarbons, aldehydes, ketones. Possessing the polar cyanopropyl moiety, sol-gel germania cyanopropyl-PDMS capillaries were found to effectively extract polar analytes such as alcohols, fatty acids, and phenols. Besides, they also showed superior thermal stability compared with commercial cyano-PDMS coatings thanks to the covalent attachment of the coating to capillary surface achieved through sol-gel technology. Their extraction characteristics remained unchanged up to 330°C which is significantly higher than the maximum operation temperature (<280°C) for commercial cyano-PDMS coatings. Low ng/L detection limits were achieved for both non-polar and polar test solutes. Our preliminary results also indicated that sol-gel hybrid germania coatings have the potential to offer great analytical performance as GC stationary phases.
Thesis:
Dissertation (Ph.D.)--University of South Florida, 2009.
Bibliography:
Includes bibliographical references.
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Mode of access: World Wide Web.
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by Li Fang.
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Title from PDF of title page.
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Document formatted into pages; contains 183 pages.
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Includes vita.

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aleph - 002220459
oclc - 645289577
usfldc doi - E14-SFE0002853
usfldc handle - e14.2853
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SFS0027170:00001


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ABSTRACT: For the first time, germania-based hybrid organic-inorganic sol-gel materials were developed for analytical sample preparation and chromatographic separation. Being an isostructural analog of silica (SiO), germania (GeO) is compatible with silica network. This structural similarity, which is reflected by the relative positions of germanium and silicon in the periodic table, stimulated our investigation on the development of germania-based sol-gel hybrid organic-inorganic coatings for analytical applications. Sol-gel sorbents and stationary phases reported to date are predominantly silica-based. Poor pH stability of silica-based materials is a major drawback. In this work, this problem was addressed through development of germania-based organic-inorganic hybrid sol-gel materials.For this, tetramethoxygermane (TMOG) and tetraethyoxygermane (TEOG) were used as precursors to create a sol-gel network via hydrolytic polycondensation reactions to provide the inorganic component (germania) of the organic-inorganic hybrid coating. The growing sol-gel germania network was simultaneously reacted with an organic ligand that contained sol-gel-active sites in its chemical structure. Hydroxy-terminated polydimethylsiloxane (PDMS) and 3-cyanopropyltriethoxysilane (CPTES) served as sources of nonpolar and polar organic components, respectively. The sol-gel reactions were performed within fused silica capillaries. The prepared sol-gel germania coatings were found to provide excellent pH and thermal stability. Their extraction characteristics remained practically unchanged after continuous rinsing of the sol-gel germania-PDMS capillary for 24 hours with highly basic (pH=13) and/or acidic (pH = 1.3) solution.They were very efficient in extracting non-polar and moderately polar analytes such as polycyclic aromatic hydrocarbons, aldehydes, ketones. Possessing the polar cyanopropyl moiety, sol-gel germania cyanopropyl-PDMS capillaries were found to effectively extract polar analytes such as alcohols, fatty acids, and phenols. Besides, they also showed superior thermal stability compared with commercial cyano-PDMS coatings thanks to the covalent attachment of the coating to capillary surface achieved through sol-gel technology. Their extraction characteristics remained unchanged up to 330C which is significantly higher than the maximum operation temperature (<280C) for commercial cyano-PDMS coatings. Low ng/L detection limits were achieved for both non-polar and polar test solutes. Our preliminary results also indicated that sol-gel hybrid germania coatings have the potential to offer great analytical performance as GC stationary phases.
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Germania Based Sol Gel Org anic Inorganic Hybrid Coatings f or Capillary Microextraction by Li Fang 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, Ph.D. Jennifer Lewis, Ph.D. Robert Potter, Ph.D. Date of Approval: April 1, 2009 Keywords: Sol Gel Germania Coat ing, CME, SPME, In Tube SPME, Gas Chromatography, Stationary Phase Copyright 2009 Li Fang

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DEDICATION To my parents Duohui Li and Fengshan Fang my sister Ying Fang who made this possible, for their endless love and support.

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ACKNOWLEDGEMENT I would like to express my gratitude to many people who gave me the possibility to complete this thesis I am deeply grateful to my major professor, Dr. Abdul Malik, for his supervision, patience and encouragement in the past five years I also want to present my sincere thanks to my dissertation committee members: Dr. Milton D. Johnston, Dr. Jennifer Lewis, and Dr. Robert Potter for their valuable advice, thoughtful comments and support. I would like to thank all my former and current colleagues Dr. Khalid Alhooshani, Dr. Abuzar Kabir, Dr. Tae Young Kim, Dr. Sameer M. Kulkarni, Dr. We n Li, Anne M Shearrow, Erica Turner and Scott Segro for their continuous assistance, encoura gement, and friendship. I also want to extend thanks to the Department of Chemistry for financial support over the past five years

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i TABLE OF CONTENTS LIST OF TABLES ................................ ................................ ................................ ............ v i i LIST OF FIGURES ................................ ................................ ................................ ........... i x LIST OF SCHEMES ................................ ................................ ................................ ......... x ii LIST OF S YMBOL S AND ABBREVIATIONS ................................ ............................ xiii ABSTRACT ................................ ................................ ................................ ....................... x v CHAPTER ONE : BACKGROUND OF SOLID PHASE MICROEXTRACTION (SPME) ................................ ................................ ................................ ....................... 1 1.1 Introduction to sample preparation ................................ ................................ ....... 1 1.2 Introduction to classical sample preparation approaches ................................ ...... 2 1.2.1 Liquid liquid extraction (LLE) ................................ ................................ .... 2 1.2.2 Soxhlet extraction ................................ ................................ ........................ 3 1.3 Solvent free extraction ................................ ................................ .......................... 3 1.3.1 Gas phase extraction ................................ ................................ .................... 5 1.3. 2 Supercritical fluid extraction (SFE) ................................ ............................. 6 1.3. 3 Membrane extraction ................................ ................................ ................... 7 1.3. 4 Solid phase extraction (SPE) ................................ ................................ ....... 8 1.4 Introduction of exhaustive extraction and no n exhausive extraction techniques ................................ ................................ ................................ ............. 8 1 .5 Introduction to solid phase microextraction ................................ ....................... 1 0

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ii 1. 5 .1 SPME device and application ................................ ................................ .... 1 1 1. 5 2 Theoretical aspect of SPME ................................ ................................ ....... 1 3 1.6 Conventional SPME coating ................................ ................................ ............... 1 6 1. 6 1 Homegeneous polymers ................................ ................................ ............. 19 1. 6 2 Composite extraction media ................................ ................................ ...... 2 0 1. 6 3 Emerging extraction medi a ................................ ................................ ........ 2 0 1.7 Different formats of SPME ................................ ................................ ................. 2 1 1. 7 1 Fiber SPME ................................ ................................ ................................ 2 1 1. 7 1.1 Direct immersion SPME (DI) ................................ ......................... 2 2 1. 7 1.2 Headspace fiber SPME (HS SPME) ................................ ............... 2 2 1. 7 2 In tube SPME (also termed capillary microextraction (CME)) ................. 2 3 1. 7 2.1 Comparison of fiber SPME and in tube SPME .............................. 24 1. 7 2.2 Theoretical aspect of in tube SPME ................................ ............... 3 0 1. 7 2.3 Parameters influencing in tube SPME ................................ ............ 32 1. 7 3 Stir bar sorptive extraction (SBSE) ................................ ............................ 32 1. 8 References for chapter one ................................ ................................ .................. 3 4 CHAPTER TWO : SOLID PHASE MICROEXTRACTION AND SOL GEL TECHNOLOGY ................................ ................................ ................................ ....... 3 9 2.1 Introduction to sol gel process and some basic definitions ................................ 3 9 2.2 Historical background of sol gel technology ................................ ...................... 4 2 2.3 The potential of sol gel chemistry in co ating technology for analytical microextraction ................................ ................................ ................................ 4 3 2.3.1 Problems with traditio nal SPME coati ng technology ................................ 4 3

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iii 2.3.2 The advantages sol gel technology for use in analytical microextraction ................................ ................................ .......................... 4 4 2.4 Fundamentals of sol gel technology ................................ ................................ ... 4 6 2.5 Creation of sol gel CME sorbents ................................ ................................ ....... 49 2.5.1 Pre treatment of the fused silica capillary ................................ ................. 49 2.5.2 Preparation of the sol solution ................................ ................................ ... 52 2.5.3 Sol gel coating process ................................ ................................ .............. 55 2.5.4 Further treatment of sol gel coated CME capillay ................................ .... 55 2.6 Charac terization of sol gel extracting phase and its morphology ....................... 5 6 2.7 Reported sol gel coating materials in SPME and CME ................................ ...... 5 7 2.8 Drawbacks of silica based sol gel materials ................................ ....................... 6 2 2.9 Sol gel process using transition metal alkoxide ................................ .................. 62 2.10 Non silica sol gel materials in analytical microextraction and chromatographic separation ................................ ................................ .............. 67 2.11 Reference s for chapter two ................................ ................................ ............... 7 1 CHAPTER THREE : GERMANIA BASED SOL GEL HYBRID ORGANIC INORGANIC COATINGS FOR CAPILLARY MICROEXTRACTION AND GAS CHROMATOGR A PHY ................................ 8 0 3.1 Introduction of germanosilicate glasses material ................................ ................ 80 3.2 Preparation of sol gel GeO 2 /ormosil organic inorganic hybrid material ............ 82 3.3 Ormosi l precursors at low treatment temperature ................................ ............... 8 3 3.4 Problems of germanosilicate material during sol gel process ............................ 85

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iv 3.5 Introduction of Germania based s ol gel organic inorganic hybrid coatings for capillary microextraction and gas chromatography ........................ 86 3.6 Exp erimental ................................ ................................ ................................ ....... 91 3.6.1 Equipment ................................ ................................ ................................ .. 91 3.6.2 Chemicals and materials ................................ ................................ ............ 92 3.6.3 Preparation of sol gel germanis PDMS coated capillaries for CME ......... 92 3.6.4 Preparation of silica based sol gel PDMS columns for GC analysis ........ 9 4 3.6.5 Preparation of aqueous sampl es for CME GC ................................ ........... 9 4 3.6.6 Gravity fed sample dispenser for capillary microextraction ..................... 9 4 3.6.7 Sol gel capillary microextraction ................................ ............................... 95 3.6.8 Safety precautions ................................ ................................ ...................... 96 3.7 Results and discussion ................................ ................................ ........................ 96 3.7.1 Chemical reactions involved in the preparation of sol g el g ermania coatings ................................ ................................ ................................ ...... 96 3.7.2 IR Characterization ................................ ................................ .................. 1 03 3.8 CME profile for sol gel Germania coated capillaries ................................ ....... 1 03 3.9 Extraction characteristics of sol gel germania coatings in CME ...................... 106 3.9.1 Extraction of non polar and moderately polar compounds by so l gel g ermani a PDMS coated capillary for CME GC analysis ........................ 1 06 3.9.2 pH stability of sol gel germania PDMS coated capillary ........................ 1 1 3 3.9.3 Extraction of polar compounds by sol gel g ermania CME GC ............... 1 14 3.9.4 GC separation of sol gel g ermania PDMS coated column ...................... 1 19 3.10 Conclusion ................................ ................................ ................................ ...... 1 22

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v 3.11 Reference s for chapter four ................................ ................................ ............. 1 22 CHAPTER FOUR : MIXED GERMANIA SILICA SOL GEL CYANOPROPYL POLY(DIMETHYLSILOXANE) COATING FOR CAPILLARY MICROEXTRACTION OF POLAR ORGANIC TRACE CONTAMINANTS IN AQUEOUS MEDIA ................................ ......................... 1 28 4.1 Introduction ................................ ................................ ................................ ....... 1 28 4.2 Experimental ................................ ................................ ................................ ..... 1 32 4.2.1 Equipment ................................ ................................ ................................ 1 32 4.2.2 Chemicals and materials ................................ ................................ .......... 155 4.2.3 Preparation of sol gel germanis CN/PDMS coated capillaries for CME ................................ ................................ ................................ ......... 133 4.2.4 Preparation of aqueous samples for CME GC ................................ ......... 1 34 4.2.5 Sol gel capillary microextraction by an in lab gravity fed sample dispenser ................................ ................................ ................................ .. 1 35 4.3 Results and discussion ................................ ................................ ...................... 136 4.3.1 Chemical reactions involved in the preparation of sol gel g ermania CN/PDMS coatings ................................ ................................ 1 36 4.3.2 Extraction profiles for sol gel germania CN/PDMS capillarie s .............. 1 40 4.3.3 Extraction characteristics of sol gel germania CN/PDMS in CME ........ 1 44 4.3.4 Thermal stability of sol gel germania coatings in CM ............................ 1 54 4.4 Conclusion ................................ ................................ ................................ ........ 1 56 4.5 Reference s for chapter five ................................ ................................ ............... 1 56 APPENDICES ................................ ................................ ................................ ................. 1 60

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vi Appendix A: Germia based, sol gel hybird organic inorganic c o ating s for capillary microextraction and gas chromatography ................................ .......... 1 6 1 Appendix B: Sol gel immobilized cyano polydimethylsiloxane coatings for capillary microextraction of aqueous trace analytes ranging from polycyclic aromatic hydrocarbons to free fatty acids ................................ ....... 1 7 2 ABOUT THE AUTHOR ................................ ................................ ................... END PAGE

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vii LIST OF TABLES Table 1.1 Commercial SPME coating s and their properties ................................ .............. 18 Table 2 .1 O rganic sorbents and their applications ................................ ............................. 5 8 Table 3 .1 Chemical ingredients of the coating solu tion used in preparing sol gel g e rmania organic inorganic hybrid coatings ................................ ............................ 9 8 Table 3 2 GC p eak area and retention time repeatability data for PAHs, aldehydes, and ketones extracted from aqueous samples by CME using a sol gel germania PDMS coated microextraction capillary ................................ ................. 1 07 Table 3 3 D etection limit data for PAHs, aldehydes, and ketones extracted from aqueous samples by CME GC using a sol gel germania PDMS coated microextraction capillary ................................ ................................ ........................ 1 08 Table 3 4 Capillary to capillary reproducibility (n=3) data for extracted amounts in CME GC ex periments conducted on sol gel germania PDMS coated capillaries using a PAH (phenanthrene), an aldehyde (undecanal), and a ketone (hexanophenone) as test solutes ................................ ................................ .............. 1 09 Table 4 1 Chemical ingredients of the coating solution used in preparing sol gel germania organic inorganic hybrid coatings chemically anchored to the inner surface of a fused silica capillary ................................ ................................ ............ 1 38

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viii Table 4 2 GC p eak area and retention time repeatabilit y data (n= 4 ) for chlorophenols alcohols, free fatty acids and ketones extracted from aqueous samples by CME using sol gel germania CN/PDMS coated microextraction capillary ................................ ................................ ................................ ................... 1 45 Table 4 3 GC FID d etection limit data (n=4) for chlo rophenols, alcohols, free fatty acids and ketones extracted from aqueous samples by CME using sol gel germania CN/PDMS c oated microextraction capillary ................................ .......... 146 Table 4 4 Capillary to capillary reproducibility (n=3) data for extracted amounts in CME GC experiments conducted on sol gel germania CN/PDMS coated capillaries using a chlorophenol (pentachlorophenol), an alcohol (unde canol), a free fatty acid (undecanoic acid) and a ketone (heptanophenone) as test solutes ................................ ................................ ................................ ..................... 1 47

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ix LIST OF FIGURES Figure 1.1 Classification of Solvent free extraction techniques ................................ .......... 5 Figure 1.2 Classification of the extraction techniques ................................ ....................... 1 0 Figure 1.3 Schematic of a SPME device ................................ ................................ ........... 1 2 Figure 1.4 Extraction step for SPME ................................ ................................ ................. 1 3 Figure 1.5 Principle of SPME ................................ ................................ ............................ 14 Figure 1.6 Modes of SPME operation ................................ ................................ ............... 2 3 Figure 1.7 Comparison SPME fiber with in tube SPME ................................ ................... 2 4 Figure 1.8 Comparison of extraction process for the tra nsf er of analytes in fiber SPME and in tube SPME ................................ ................................ ......................... 25 Figure 1.9 Illustration of extraction procedure of extraction by fiber SPME and analyte desorption for HPLC analysis ................................ ................................ ...... 2 8 Figure 1. 10 Schematic diagrams of in tube SPME LC MS systems ................................ 2 9 Figure 1.11 Distribu tion of analyte between sample matrix and the extraction phase ...... 3 0 Figure 1. 12 Schematic of a stir bar of SBSE ................................ ................................ ..... 3 3 Figure 2.1 Overview of the Sol gel process ................................ ................................ ....... 4 1 Figure 2.2 Homemade capillary filling/purging device ................................ ..................... 5 1 Figure 3.1 A FTIR spectra representing: p ure PDMS ................................ ..................... 1 04 Figure 3.1 B FTIR spectra represent ing: sol gel germania PDMS hybrid material used as a sorbent in capillary microextraction ................................ ........................ 1 04

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x Figure 3.2 Capillary microextraction profiles of pyrene and heptanophenone on a sol gel germania coated capillar y ................................ ................................ ........... 1 05 Figure 3.3 CME GC trace analysis of a mixture of PAHs using a sol gel germania PDMS coated microextraction c apillary ................................ ................. 1 11 Figure 3.4 CME GC tr ace analysis of a mixture of aldehydes and ketones using a sol gel germania PDMS coated microextraction c ap illary ................................ ..... 1 1 2 Figure 3.5 CME GC trace analysis of alcohols using a sol gel germania APTMS coated microextraction c apillary ................................ ................................ ............. 1 15 Figure 3.6 Excellent stability of sol gel germania PDMS coating under highly basic conditions demonstrated through CME GC analysis of a mixture of PAHs using a sol gel germania PDMS coated microextraction capillary before ( 3.6 A) and after ( 3.6 B) continuously rinsing the capil lary with a 0.1 M NaOH solution (pH = 13) for 24h ................................ ................................ ........... 1 1 6 Figure 3.7 Excellent stability of sol gel germania P DMS coating under highly acidic conditions demonstrated through CME GC analysis of aldehydes using a germania PDMS coated microextraction capillary before ( 3.7 A) and after ( 3.7 B) continuously rinsing the capillary with a 0.05 M HCl solution for 24 h ................................ ................................ ................................ .................... 1 1 7 Figure 3.8 CME GC trace analysis of 2, 4, 6 Trichlorophenol using a sol gel germania PDMDPS coated microextraction capillary ................................ ............ 1 18 Figure 3.9 CME GC analysis of free fatty acids using a sol gel germania APTMS coated microextraction capillary ................................ ................................ ............. 1 20

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xi Figure 3.10 Gas chromatogram of a natural gas sample separated on sol gel germania PDMS stationary phase ................................ ................................ ........... 1 21 Figure 4.1 Capillary microextraction profiles of undecanol, heptanophenone, pentachlorophenol on a sol gel germania CN/PDMS coated capillary .................. 1 43 Figure 4. 2 CME GC analysis of a mixture of alcohols using a sol gel germania CN/PDMS coated microextraction capillary ................................ .......... 1 49 Figure 4.3 CME GC analysis of a mixture of acids using a sol gel germania CN/PDMS coated microextraction capillary ................................ .......... 151 Figure 4.4 CME GC analy sis of a mixture of chlorophenols using a sol gel germania CN/PDMS coated microextraction capillary ................................ .......... 1 52 Figure 4.5 CME GC analysis of a mixture of ketones using a sol gel germania CN/PDMS coated microextraction capillary ................................ .......... 1 53 Figure 4.6 Effect of conditioni ng temperature on the performance of sol gel germania CN / PDMS microextraction capillary in the extraction of nonanol ........ 1 55

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xii LIST OF SCHEMES Scheme 2.1 Illustration of hydrolysis and condensation of tetramethoxysilane (TMOS) ................................ ................................ ................................ ..................... 49 Scheme 2.2 Deactiv ating reagents ................................ ................................ ..................... 5 3 Scheme 2.3 Deactivation of silica surface with HMDS ................................ .................... 54 Scheme 2.4 General sol gel process for transitional metal alkoxides ............................... 64 Scheme 2.5 Mechanisms of sol gel hydrolysis and condensation reactions of metal alkoxides ................................ ................................ ................................ ................... 65 Scheme 3.1 Typical hydrolytic ploycondensation of g ermanium alkoxide to form g ermania ................................ ................................ ................................ .................... 8 2 Scheme 3.2 Hydrolysis of sol gel germania precursor TMOG ................................ ........ 9 9 Scheme 3.3 Polycondensation of the hydrolyzed precursor and chemical bonding of the sol gel active organic ligand (Y) to th e evolving sol gel network ............... 1 00 Scheme 3.4 Chemical anchoring of the evolving sol gel germania hybrid organic inorganic polymer to the inner walls of a fused silica capillary ................ 101 Scheme 4.1 Hydrolysis of sol gel germania precursor (TEOG) ................................ ...... 1 40 Scheme 4.2 Poly condensation of the hydrolyzed precursor and chemical bonding of the sol gel active organic ligand (Y) to the evolving sol gel network ............... 1 4 1 Scheme 4.3 Chemical anchoring of the evolving sol gel germania hybrid organic inorganic polymer to the inner walls of a fused silica capillary ................ 1 42

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xiii LIST OF SYMBOLS AND ABBREVIATIONS A N N ucleophilic A ddition AFM A tomic F orce M icroscopy AMTEOS Anilinemethyltriethoxysilane APTMS 3 A minopropyltrimethoxysilane BMA Butyl methacrylate C 8 TEOS n Octyltriethoxy silane CE C apillary E lectrophoresis CEC C apil lary E lectrochromatography CME C apillary M icroextrac tion CME GC Capillary Microextraction Gas Chromatography CPs Chlorophenols CPTES 3 C yanopropyltriethoxysilane CVD C hemical V apour D eposition CW/DVB C arbowax/divinylbenzene CW/TPR C arbowax/templated resin CW C arbowax DCCA D rying C ontrol C hemical A dditive DEOS D iethylorthosilicate DHS D ynamic H eadspace DVB Divinyl benzene EPA Environmental Protection Agency EVP ICP MS Environmental Vaporiza tion Inductively Coupled Plasma Mass Spectrometry FA F ormic A cid FID F lame I onization D etector GC G as C hromatography GC MS Gas Chromatography Mass Spectrometry GLYMO G lycidoxypropyltrimethoxysilane GODC Germanium O xygen D eficient C enters HMDS 1,1,1,3,3,3 Hexamethyldisilazane HPLC H igh P erforma nce L iquid C hromatography HS SPME Headspace Solid Phase Microextraction ICP MS Inductively Coupled Plasma Mass Spectrometry INC AT I nside N eedle C apillary A dsorption T rap LC MS Liquid Chromatography Mass Spectrometry LLE L iquid L iquid E xtraction MA Methyl acrylate MMA Methyl methacrylate

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xiv MS Mass S pectrometry MSDS M aterial S afety D ata S heet MTES Methyltrimethoxysilane MTMOS M ethyltrimethoxysilane NMR N uclear M agnetic R esonan ce OH TSO H ydroxyl terminated polydimethylsiloxane ppq Parts Per Quadrillion ppt Parts P er T rillion poly THF Polyt etrahydrofuran PA P olyacrylate PAHs Polycyclic A romatic H ydrocarbons PDMDPS P olydimethyldiphenylsiloxane PDMS P olydimethylsiloxa ne PDMS/DVB P olydimethylsiloxane/divinylbenzene PEG P olyethylene glycol PheDMS P henyldimethylsiane PMHS P oly(methylhydrosiloxane) PMPS Polymethylphenylsiloxane PMPVS P oly (methylphenylvinylsiloxane) PTFPMS Poly(trifluoropropyl)methylsiloxane PVA P oly (vinyl alcohol) R.S.D Relative Standard Deviation S N N ucleophilic S ubstitution SBSE Stir B ar S orptive E xtraction SCF S upercritical F luids SEM Scanning E lectron M icroscopy SFE S upercritical F luid E xtraction SHG S econd H armonic G ener ation SHS S tatic H ead space SPE S olid P hase E xtraction SPME Solid P hase M icroextraction SPME GC Solid Phase Microextraction Gas Chromatography SPME HPLC Solid Phase Microextraction H igh P erforma nce L iquid Chromatography SPME HP LC MS Solid Phase Microextraction H igh P erforma nce L iquid Chromatography Mass Spectrometry TEOG T etraethyoxygermane TEOS T etraethoxysilane TFA T rifluoroacetic A cid THF T etrahydrofuran TMOG T etramethoxygermane TP i OG G ermanium iso propoxide TPO G T etrapropyloxygermane VOCs V olatile O rganic C ompounds XPS X ray P hotoelectron S pectroscopy

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xv G ERMANIA BASED SOL GEL ORGANIC INORGANIC HYBRID COATINGS FOR CAPILLARY MICROEXTRACTION Li Fang ABSTRACT For the first time germania based hybr id organi c inorganic sol gel materials were developed for analy tical sample preparation and chromatographic separation. Being an isostructural analog of silica ( SiO 2 ) germania ( GeO 2 ) is compatible with silica network. This structural similarity, which is reflecte d by the relative positions of germanium and silicon in the periodic table, stimulated our investiga tion on the development of g ermania based s ol gel hybrid organic inorganic coatings for analytical applications Sol gel sorbents and stationary phases re ported to date are predominantly silica based. Poor pH stability of silica based materials is a major drawback. In this work, this problem was addressed through development of germania based organic inorganic hybrid sol gel materials. For this, t etramethox ygermane (TMOG) and t etraethyoxygermane (TEOG) w ere used as precursor s to create a sol gel network via hydrolytic polycondensation reactions to provide the inorganic component (g ermania ) of the organic inorganic hybrid coating. The growing sol gel germani a network was simultaneously reacted with an organic ligand that contained sol gel active sites in i ts chemical structure. H ydroxy terminated polydimethylsiloxane ( PDMS ) and

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xvi 3 c yanopropyltriethoxysilane ( CPTES ) served as sources of nonpolar and polar orga nic component s, respectively T he sol gel reactions were performed within fused silica capillar ies The prepared sol gel germania coatings were found to provide excellent pH and thermal stability Their e xtraction characteristics remained practically unc hanged after continuous rinsing of the sol gel germania PDMS capillary for 24 hours with highly basic (pH = 13) and/or acidic (pH = 1.3) solution They were very efficient in extracting non polar and moderately polar analytes such as polycyclic aromatic hy drocarbons, aldehydes, ketones Possessing the polar cyanopropyl moiety, sol gel germania c yanopropyl PDMS capillaries were found to effectively extract polar analytes such as alc ohols, fatty acids, and phenols Besides, they also showed superior thermal stability compared with commercial cyano PDMS coatings thanks to the covalent attachment of the coating to capillary surface achieved through sol gel technology. Their extraction characteristics remained unchanged up to 330 C which is significantly high er than the maximum operation temperature (< 280 C ) for commercial cyano PDMS coatings Low ng/L detection limits were achieved for both non polar and polar test solutes. Our preliminary results also indicate d that sol gel hybrid germania coatings have the potential to offer great analytical performance as GC stationary phases

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1 CHAPTER ONE BACKGROUND OF SOLID PHASE MICROEXTRACTION (SPME) 1.1 Introduction to sample preparation The analytical procedure for complex samples consists of several typica l steps: sampling, sample preparation, separation, quantification, statistical evaluation, and decision making. These analytical steps follow one after another, and a subsequent step cannot begin until the preceding one has been completed. Therefore, the s lowest step determines the overall speed of the analytical process, and each step is critical for obtaining correct and informative results. To improve analysis speed, all the steps should be considered. Sample preparation as a part of the analysis takes about 80 % of analysis time for complex samples [1]. One reason is the difficulty to couple sampling and sample Chromatography/Mass Spectrometry (GC/MS) or Liquid Chromatography/Mass Spec trometry (LC/MS). Those sophisticated instruments, can separate and quantify complex mixtures and automatically apply chemometric methods to statistically evaluate results. D espite the advances in separation and quantitation techniques, many sample prepara tion techniques are based on classical technologies such as Soxhlet extraction method are time consuming and involve multi step procedures that are prone to los e analyte loss use of the toxic organic solvents. These characteristics make it extremely diffic ult to integrate such methods sophisticated separation and quantitation

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2 instruments for the purpose of automation. Another reason is that often one has to deal with real world complex or natural samples, therefore the fundamentals of extractio n techniques involving them are much less well developed and understood compared well defined physicochemical principles governing instrument used in separation and quantification steps. Lastly, a new awareness of the hazards has resulted in international initiatives [2] to develop new sample preparation techniques aimed at complete elimination of using organic solvents that we used in large volume by classical sample preparation techniques 1.2 Introduction to classical sample preparation approaches It is not an exaggeration to say that choice of sample preparation method greatly influences the analytical reliability, efficiency and accuracy. Soxhlet extraction for solid samples [ 3 ] and liquid liquid extraction (LLE) for liquid samples [ 4 6 ] are two most c ommonly used classical sample preparation approaches 1.2.1 L iquid liquid extraction (LLE) L iquid liquid extraction involves the use of an organic solvent to extract analytes from aqueous samples in reparatory funnels or other vessels. It is one of the ol dest techniques and still is widely used. Many of the US EPA standard methods for organic trace analysis still utilize LLE. The main disadvantage of the technique is the use of large quantity of organic solvents, which might be expensive to buy and dispose of, and cause environmental problem and potential health concerns. It is also very difficult to couple LLE technique with any other instrumental analysis systems. LLE is not easily automated.

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3 Lastly, the enrichment fact or is quite limited and for many sam ple types there are problems with emulsion formation and precipitation. 1.2.2 Soxhlet extraction Soxhlet extraction technique has been the most widely used method for exhaustive extraction analytes from solid samples. Typically, a Soxhlet extraction is us ed where the target analyte has a limited solubility in a solvent and the matrixes are possible impur ities are insoluble in that solvent. Because a simple filtration can be used to separate the compound easily from the insoluble su bstance it is desirable that the target analytes has a high solubility in the solvent. Soxhlet extraction normally involves placing the solid sample in the porous cellulous thimble placed in a holder. During operation the thimble is filled with fresh warm organic solvent from a distillation flask. During the process of extraction, the extracted analytes accumulate in the solvent and are automatically siphoned into the distillation flask regularly. These steps are repeated until exhaustive extraction of the target is achieved. Although the soxhlet technique uses inexpensive equipment to operate, the processes involved are quite slow and may require the use of large amounts of hazardous solvent s causing concerns about the environment and human health At the s ame time, the used solvents are highly costly to be disposed of. 1.3 Solvent free extraction Classical sample preparation technique s consume large amounts of solvents. During the volume reduction step, waste solvents are often disposed into the environme nt. Solvent disposal into the atmosphere causes pollution and contributes to unwanted

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4 atmospheric effects such as smog and ozone holes. In addition, solvent disposal adds extra cost to the overall analytical process by complicating work of the regulatory a gencies, and it increases health hazards to laboratory personnel. The desire for efficient extractions while consuming less solvent has led to a trend on increased research on new and practical solvent free alternatives A few of these research areas inclu de Gas phase extractions [7 8] supercritical fluid extraction (SFE) [9 11] membrane extraction [ 12 13 ] and solid phase extraction (SPE ) [14 17] Solvent free extraction techniques [6] [18] have been an important direction to address the problems associate d with classical sample preparation methods. Solvent free sample preparation techniques use little or no organic solvent. This direction not only addresses health and pollution prevention issues, but also in most cases provides an easier way to implement o n site monitoring in field conditions. This direction has been creating a lot of interests and research opportunities recently and it is expected to continue to be a very active area in the near future. Solvent free extraction techniques can be broadly cla ssified as shown in the Figure 1 1 into gas phase, membrane and sorbent extraction techniques

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5 Figure 1 1 Classification of Solvent free extraction techniques [ 19 ] 1.3.1 Gas phase extraction Gas phase extraction s can be carried out in two different modes static head space (SHS) and dynamic head space (DHS) ( also known as purge and trap) [ 7, 8 ] In s tatic head space mode the volatile analytes in the sample matrix diffuse into the headspace in a vial, and the conc entration of the analyte in the headspace reaches equilibrium with the concentration in the sample matrix After the equilibrium is established a small volume of the head space gas is injected into a GC. Using static headspace method has the advantages of simplicity. It is more convenient for qualitative analysis since the sample can be placed directly into the headspace vial and analyzed with no additional preparation. However, t his technique suffers from low sensitivity because there is no mechanism of s ample preconcentration DHS potentially provides improved sensitivity when compared with SHS, due to the constant depletion of the analytes from the sample. In dynamic head Solvent Free Sample Preparation Methods Membrane Extraction Gas Phase extraction Sorbent Extraction SPE SPME Cartridge Disk Direct Headspace In tube Headspace Dynamic Static Dynamic Stat ic SFE

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6 space, carrier gas is bubbled through solid or liquid sample s containing volatile o rganic compounds (VOCs), are subsequently in a sorbent trap The carrier gas sweeps volatile organic compounds into the sorbent trap. Desorption of trapped analytes for subsequent analysis can be performed either with small volumes of appropriate solvent s or using an on line automated thermal desorption device, the la t ter is suitable for routine procedures. 1.3.2 Supercritical fluid extraction (SFE) Supercritical fluid extraction [ 9 11 ] is an attractive technique because it is fast and selective This extr action technique is based on the fact that near critical conditions of the solvent, its properties change rapidly with only slightly variations of pressure. A supercritical fluid extractor typically consists of a tank of the extracting fluid usually liqui d CO 2 a pump to pressurize CO 2 an oven containing the extraction vessel, a restrictor to maintain a high pressure in the extraction line, and a trapping vessel. Analytes are trapped by letting the solute containing supercritical fluid decompress into an empty vial, through a solvent, or onto a solid sorbent material. Ex tractions are done in dynamic static or combination modes. In a dynamic SFE, the supercritical fluid continuously flows through the sample in the extraction vessel and out the restricto r to the trapping vessel. In static mode the supercritical fluid circulates in a loop containing the extraction vessel for some period of time before being released through the restrictor to the trapping vessel. In the combination mode, a static extraction is performed for so me period of time, followed by dynamic extraction. Several compounds have been examined as SFE solvents. For example, hydrocarbons such as hexane, pentane and butane, nitrous oxide, sulphur hexafluoride and fluorinated hydrocarbons [20] However, carbon dioxide

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7 (CO 2 ) is the most popular SFE solvent because it is safe, readily available in highly pure form and has a low cost. It allows supercritical operations at relatively low pressures and at near room temperatures. The main drawback of CO 2 is its lack of polarity for the extraction of polar analytes [ 21 ] Compared with other traditional extraction techniques, it is a flexible process due to the possibility of continuous modulation of the solvent power/selectivity of the supercritical fl uids (SCF), and it is also environmental friendly than organic solvents and avoids the expensive post processing of the extracts for solvent elimination B ecause of these advantages, carbon dioxide (CO 2 ) is the most widely used supercritical solvent. A ser ious drawback of SFE is the higher investment costs compared to traditional atmospheric pressure extraction techniques. The interest in SFE has dramatically declined because of the dependence of the extraction on sample condition. This dependency makes the technique difficult for routine analysis due to the tedious optimization procedure which is required to overcome this problem. Furthermore, SFE requires liquid like compressed CO 2 as the extraction medi um The high cost of pure CO 2 and overall design of S FE makes the technique incompatible with field analyses [ 22 24 ] 1.3.3 Membrane extraction Membr ane extraction [12, 13] can be divided into two categories, por ou s and non po rou s membrane techniques. The por ou s membrane techniques involve filtration and dia lysis in different formats. In these techniques the solutions on both sides of the membrane are in physical contact through the membrane pores, so this is in fact a one phase system. Non pores membrane techniques involve a membrane that is either a polymer ic material or a liquid separating the donor and acceptor. In these techniques, it

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8 could be two phase or three phase system. Membr ane extraction consist s of two simultaneous process es. In the first step, a membrane is used to extract analyte from the matri x. This step is followed by extracting the analyte from the membrane surface with a stripping phase. This method is only suitable for non polar volatile and semivolatile compounds. The major limitations of membrane extraction include slow response, carryov er, and difficulty in interfacing the techni que with other instrumentation [17, 18, 25, 26] 1.3.4 Solid phase extraction (SPE) Solid phase extraction [14 17] is based on the selective accumulation of target analytes from a liquid matrix onto a sorbent be d. SPE has several formats including cartridge tube, flat disk membrane, monolithic bed, and flow through membrane containing a sorbent on a particulate support. The major advantages of the technique are the significant reduction in the use of organic solv ent, ease in operation, and low cost. However, in some cases the extraction solvent may not be compatible with an analytical system. To overcome this, the solvent is evaporated and the remaining residue is dissolved in a compatible solvent. Furthermore, SP E has poor reproducibility and high carry over problem. 1.4 Introduction of e x haustive extraction and no n ex haustive extraction techniques The objective of exhaustive technique is to completely remove analytes from a sample matrix and transfer them to the extract ing phase. The fundamental advantage of exhaustive methods is that, in principle, they do not require calibration since the vast

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9 majority of analytes are transferred to the extracti ng phase. To reduce the amounts of solvents and time required to ac complish exhaustive removal, batch equilibrium techniques (for example, liquid liquid extractions) are frequently replaced by flow through techniques. SPE is an example in this category. Alternatively, a sample (typically a solid sample) can be packed in t he bed and the extraction phase can be used to remove and transport the analytes to the collection point. In SFE, supercritical fluid is used to wash analytes from the sample matrix, and in Soxhlet, the solvent continuously removes the analytes from the ma trix at the boiling point of solvent. On the other hand, non exhaustive approaches can be designed based on equilibrium, pre equilibrium and permeation principles. Equilibrium non exhaustive techniques are fundamentally analogues to equilibrium exhaustive techniques; however, the capacity of the extract ing phase is smaller, and in most cases is not sufficient to remove the majority of analytes from the sample matrix. This is caused by the use of a small volume of the extracting phase relative to sample volu me. Microextraction, such as solvent microextraction or solid phase microextraction is in this category. Pre equilibrium conditions are accomplished by breaking the contact between the extract ing phase and sample matrix before the point of equilibrium with the extracting phase has been reached. The devices frequently used are identical to the microextraction system, but extraction times are shorter. The general classification of the extraction techniques based on the se fundamental principles is in Figure 1 2 [19]

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10 Figure 1 2 Classification of the extraction techniques [19] 1.5 Introduction of solid phase m icroextraction Solid phase micr oextraction (SPME) is an important and practical approach to sampling and sample preparation. It was developed in 1989 by Belardi and Pawliszyn [27] to overcome the limitations inherent in solid phase extraction (SPE) and liquid liquid extraction (LLE). SPME facilitates rapid sample preparation for both laboratory and field analyses. SPME has been successfully applied to a variety of analytes in environmental [28 30] biological [31 33] food [34] drug [35 37] flavor [38] and other types of samples in hyphenation with gas chromatography (GC) [39] high performance liquid chromatogra phy (HPLC) [40] capillary electrophoresis (CE) [41] and Mass Extraction techniques Batch equilibrium and Pre equilibrium Flow through Equilibrium and Pre equilibrium Steady State Exhaustive and non Exhaustive Exhaustive Non Exhaustive LLE Soxhlet Sorbents Headspace LLME SPME Exhausti ve Purge and Trap Solvent SPE HSE SFE Non Exhaustive In tube SPME Membrane

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11 spectrometry (MS) [42]. Solid phase microextraction provides many advantages over other sample preparation techniques including: (1) It wa s a simple device which enables in situ sampling Low set up cost (2) SPME techniques eliminate the use of toxic organic solvents (green chemistry) ( 3 ) SPME is shorten the analysis time integrating sampling, extraction, sample preconcentration, and sample introduction into a single step (no intermediate ste p is necessary between extraction and analysis). ( 4 ) High sensitivity (detection limit down to part per quadrillion (ppq) level) can be easily achieved using SPME ( 5 ) SPME extraction is an equilibrium process that requires small (sample volume require) ( 6 ) The technique can be easily automated with analytical instruments (GC, HPLC, and CE) ( 7 ) SPME is portable which makes it attractive for field sampling 1.5.1 SPME d evice and application In SPME, the extracting phase is coated on the surface of a fused silica fiber (fiber format) or capillary (in tube format) The extraction in SPME is an equilibrium process of analyte distribution between the extracting phase and sample matrix. The conv entional SPME devi ce (Figure 1 3 ) is very simple; i t is based on a f iber which is housed in a specially designed syringe like apparatus. The retractable metal rod, serving as the syringe piston, is replaced by stainless steel microtubing to hold and protect the

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12 SPME fiber. Typically, 1.5 cm l ong silica rod (fiber) is used. The protective extern al coating of this SPME fiber is removed from about 0.5 cm length of the fiber of one end, and this end is attached to the syringe plunger using epoxy glue. The microtubing (needle of the syringe) protects the SPME fiber coating from mechanical damage and provides a suitable way for SPME fiber insertion and withdrawing during extraction and analysis. Sampling and sample injection occur in a manner which is identical to typical syringe injections. Figure 1 3 Schematic of a SPME devic e Adapted from [43] The fiber solid phase microextraction technique is best suited for GC (SPME GC). SPME GC generally consists of two steps: (1) extraction: the needle of the SPME device at first pierces the septum of the sample container. Af ter adjusting the depth of needle to a

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13 proper position the fiber is exposed to the sample matrix for a certain time D uring this period the analytes are extracted by the SPME coating on the outer surface of the fiber (F igure 1 4) ; (2) Injection: the analy tes are thermally desorbed from the fiber and are transferred by the carrier gas (mobile phase) to the GC separation column for further separation and analysis. In liquid chromatography, the extracted analytes are desorbed by the organic solvents (LC mobil e phase) and passed into the separation solution Figure 1 4 Extraction step for SPME [44] 1.5.2 Theoretical a spects of SPME The transport of analytes from the matrix into the coating begins as soon as the coated fiber has been place d in co ntact with the sample (Figure 1 5). SPME is a non exhaustive extraction technique, and it is based on an equilibrium distribution A nalytes continue to sorb onto the SPME coating until the equilibrium between the sample matrix and the SPME fiber coa ting is achieved Typically, SPME extraction is considered to be

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14 completed when the distribution equilibrium has been reached. In practic e this means that once equilibrium is reached, the extracted amount is constant within the limits of experimental erro r and it is independent of further increase of extraction time. The thermodynamic and kinetic fundamental s of solid phase extraction have detailed by Pawliszyn and co workers [45 48] SPME can be used for extraction from both gas and liquid samples. In bot h cases, analyte molecules are distributed between the sample matrix and the sorbent coating on the SPME fiber. Figure 1. 5 Principle of SPME [45] The distribution constant represents the ratio of analyte concentrations in the sorbent coat ing and in the sample. The analyte distribution equilibrium for liquid polymeric sorbent extraction phase is represented as:

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15 The distribution constant can be described mathematically as: (1 1) where, K fs is distribution constant between fiber coating and sample matrix, C f is analyte concentration in the sorbent coating, C o is analyte concentration in the sample. The amount of analyte in the sorbent coatin g (n f ) at equilibrium condition is as follows [45] : (1 2) Where, Vs is the volume of the sample, V f is the volume of the sorbent coating on the fiber Sinc e V f is very small (L), generally ( K fs V f << Vs ) the amount of analyte in the sorbent coating can be written as : ( 1 3) This equation ( 1 3) shows that the amount of the extracted analyte in the sorbent coating for direct SPME (no head space) is independent of the sample volume. SPME is a non exhaustively extract target analytes existing in the sample matrix, and the extraction is based on the equilibrium. This is also

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16 a theoretical basis for SPME to be used as a portable extraction technique in field analysis. In practice, there is no need to collect a defined sample prior to analyses as the fiber can be exposed directly to the ambient air, water, production steam, etc. T he amount of extracted analytes will correspond directly to its concentration in the matrix, without being dependent on the sample volume. When the sampling step is eliminated, the whole analytical process can be accelerated, and errors associated with ana lyte losses through decomposition or adsorption on the sampling container walls will be prevented. This advantage of SPME still needs to be explored practically, by developing portable field device on a commercial scale. This equation also shows that there is a direct proportionality between the sample concentration and the amount of analyte extracted, and this is the basis for analyte quantification. Furthermore, it implies that the extraction efficiency and sensitivity depend on the distribution constant. Thus, a high distribution constant, K fs is desirable to enhance selectivity and sensitivity. This can be achieved by careful selection of the fiber coating material, changing sample pH, and through the derivatization of target analyte (s). 1.6 Conven tional SPME coating Equation (1 3) indicates that the efficiency of the extraction process is dependent on the distribution constant. D istribution constant is an important parameter that characterizes properties of a certain coating and its selectivity tow ard a class of analyte with certain polarity over other s Coating volume is also related with method sensitivity, for example, thicker coating s will increase the sample load and increase the extraction

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17 sensitivity, however sometimes that will result in lon ger extraction times. Therefore, it is important to use the appropriate coating for a given application. Coating selection and design can be based on chromatographic experience, and specific coatings can be and should be designed for specific applications. Conventional sorbents for SPME can be divided into two groups [45] (a) homogeneous polymers and (b) composite extraction media consisting of a partially cross linked polymers embedded with porous particles of a second component H owever the new ly emerge d polymers such as sol gel polymer s and molecular imprinted polymer s etc can be classified as new categor ies of SPME sorbents To achieve good selectivity for the analytes of interest, the choice of most suitable coating can be based on the principle polarity will provide a better affinity. Therefore from the polarity point, it is also useful to classify conventional SPME coatings into four categories: (1) non polar, (2) moderately polar, (3) polar, and (4) highly polar. Table 1 1 shows some c ommercial SPME coating and their properties [49]

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18 Table 1 1 C ommercial SPME coating s and their properties Fibre coating Film thickness (m) Polarity Coating method Maximum opera ting temperature (C) Technique Compounds to be analysed PDMS 100 Non polar Non bonded 280 GC/HPLC Volatiles PDMS 30 Non polar Non bonded 280 GC/HPLC Non polar semivolatiles PDMS 7 Non polar Bonded 340 GC/HPLC Medium to non polar semivolatiles PDMS DVB 65 Bipolar Cross linked 270 GC Polar volatiles PDMS DVB 60 Bipolar Cross linked 270 HPLC General purpose PDMS DVB a 65 Bipolar Cross linked 270 GC Polar volatiles PA 85 Polar Cross linked 320 GC/HPLC Polar semivolatiles (phenols) Carboxen PDMS 75 Bipolar Cross linked 320 GC Gases and volatiles Carboxen PDMS a 85 Bipolar Cross linked 320 GC Gases and volatiles Carbowax DVB 65 Polar Cross linked 265 GC Polar analytes (alcohols) Carbowax DVB a 70 Polar Cross linked 265 GC Polar analytes (alcohols ) Carbowax TPR 50 Polar Cross linked 240 HPLC Surfactants DVB PDMS Carboxen a 50/30 Bipolar Cross linked 270 GC Odors and flavors a Stableflex type is 2 cm length fiber

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19 1.6.1 Homogeneous polymers PDMS coated SPME fibers are commercially available in t hree different thickness es (7, 30, and 100 m), and commercial polyacrylate (PA) fibers have a coating thickness of 85 m [50, 51] These coatings extract analytes through an absorption mechanism, where the analytes dissolve and diffuse onto the coating ma terial. PDMS fibers are the most popular and frequentl y used polymer in SPME because of its inherent versatility, ruggedness, and high thermal stability The PDMS fiber with 7 m coating thickness is cross linked, while the other two are not. This is beca use it is very difficult to stabilize thick coatings through cross linking reactions. Compared with maximum operating temperature ( 280 C ) of 30 and 100 m PDMS coatings, 7 m PDMS coating possesses higher operating temperature ( 340 C ). Cross linked SPME fiber coatings are more rigid and are characterized by relatively high thermal stability compared to non cross linked or partially cross l in ked counterparts. That may explain the different thermal stability of these three types of PDMS coatings. However, c ross linked PDMS coating possesses smaller sample capacity due to the smaller coating thickness of 7 m Since PDMS is non polar in nature, it can only extract non polar analytes very well. More polar compounds can be extracted by optimizing extraction con ditions such as pH, salt effect, and temperature however they are not efficient for extraction of polar analytes. P olyacrylate (PA) based coating s [52, 53] are more suitable for the extraction of polar analytes. C ommercial PA is available in 85 m thickness and it is a highly polar sorbent, immobilized by partial crosslinking. Because of its high polar ity PA coated fiber frequently recommended for extracting polar analytes from different matrices. Unlike

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20 other sorbent s at room temperature, polyacrylate is a rigid, low density solid polymer. Therefore diffusion of analytes into this coating requires longer time resulting in longer extraction time. Moreover, higher temperatures are required for complete desorption of the extracted analytes. 1.6.2 Composite extraction media Composite extraction coatings are prepared using a blend of two components in which the particulate component is embedded in the partially crosslinked polymeric component. Among the mixed coatings are carbowax/divinylbenzene (CW/DVB) [54] polydimethylsiloxane/divinylbenzene (PDMS/DVB) [55] polydimethylsiloxane/carboxane (PDMS/carboxane) [56] and carbowax/templated resin (CW/TPR) [56] Such composite coatings usually extract via adsorption, which is a competitive process. In mixed phases t he analytes stay on the surface of SPME coatings. The mixed phases provide better selectivity due to the existence of two sorbents in the coating. However unlike the preparation of homogeneous polymeric coatings, the process to make composite coatings is d ifficult to automate and it is usually done manually. 1.6.3 E merging extraction media C ommercially available fibers are limited to the scale of polarity C onsequently this either limit s the selectivity in structural analogues analysis or prevent s the se nsitivity of trace level analysis in complex sample analysis [57] In recent years homemade coatings with different chemical and physical characteristics [58 62] have been reported. These include fullerene [58, 59] crown ester [60, 61] and calixarene bas ed [62] coatings that provide increased sensitivity and selectivity. Fiber coating procedures have been

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21 recently reviewed [63] and include sol gel technology [64] electrochemical me thods [65 66 ] and physical deposition [67] Among them, sol gel technol ogy is gradually turning to be an important coating technology to prepare all kinds of customized extracti on media, and the resultant sol gel organic inorganic polymeric material s ha ve been widely used to meet application selectivity and sensitivity. Molec ularly imprinted polymers have also been introduced as extracti ng phase s for SPME. T hey have a great potential for selective extraction of target analytes from various complex matrices. 1.7 Different format s of SPME 1.7.1 Fiber SPME As the dominant forma t of S olid phase microextraction, F iber SPME possesses a number of inherent deficiencies arising from the fiber construction and its syringe based mechanical operation. In fiber SPME, the protective polyimide coating is removed from the external surface of a fused silica fiber end segment (~ 1 cm). Therefore the fiber and the outside sorbent layer is vulnerable to mechanical damage during operation and handling of the SPME device due to the lack of external protective coating. The short length (~ 1 cm) of t he coated segment results in low sorbent loading, which leads to reduced extraction sensitivity. Moreover, fiber SPME is difficult to couple to high performance liquid chromatography (HPLC) and other liquid phase separation techniques. A number of SPME var iants have been proposed to overcome these difficulties such as membrane extraction, in tube microextraction, and stir bar sorptive extraction (SBSE), etc.

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22 1.7.1 .1 Direct immersion SPME (DI) Fiber SPME can be carried out in two different modes: (1) dire ct immersion SPME and (2) headspace SPME (Figure 1 6 ). In direct SPME, the coated segment of SPME fiber is inserted into the sample matrix containing the target analytes directly. Under agitation, the target analytes distribute between the sample matrix an d solid phase on the fiber. The equilibrium will be reached after a certain period of time. When extraction is carried out in aqueous solution, different means of agitation such as stirring or sonication of the solution, rapid fiber or vial shaking, and fa st flow of the aqueous solution may be employed to fasten the extraction. When the sample matrix is gaseous sample, natural convection of the air or the use of a fan may be employed to speed up the extraction. 1.7.1.2 H eadspace f iber SPME (HS SPME) In head space fiber SPME, the coated fiber stays in the headspace (the gaseous phase) above the liquid sample in a sealed container. The analyte distribution equilibrium is first reached between the sample matrix (either liquid or solid) and the headspace of the c losed container. After the coated fiber is introduced, the extraction wi ll be carried out from gaseous headspace to the extracting phase on the fiber. Headspace SPME can avoid unwanted interferences from sample matrix such as compo unds having high molecula r mass (e.g., humic materials, poteins, etc ) During extraction, those high molecular mass molecules characterized by low vapor pressure, stay in the liquid or solid but the small target anaytes and other small molecules characterized by big vapor pressur e distribute themselves between the sample matrix the headspace Compared with direct SPME, a

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23 certain temperature is often used to help the evaporation of target analytes into the gaseous headspace of the container. Headspace SPME allows the modification o f the matrix such as pH change, addition of salts etc to improve the extraction efficiency of the coatings without any harm to the coating on the fiber. However, for this extraction mode, the target analytes cannot be non volatile, only volatile or semi vo latile compounds can be extracted from headspace with enough sensitivity. Figure 1 6 Modes of SPME operation: (a) direct extraction, (b) headspace SPME 1.7.2 In tube SPME (also termed capillary microextraction (CME)) In tube SPME (a lso termed capillary microextraction (CME)) [68 70 ] is practically free form the shortcomings inherent in conventional fiber SPME. Unlike fiber SPME, where a sorbent coating on the outer surface of a small diameter solid rod s erves as the extraction mediu m in CME a piece of fused silica capillary with a stationary phase

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24 coating on its inner surface (e.g., a short piece of GC column) is typically used to perform extraction (Figure 1 7) In the capillary format the protective polyimide coating on the exter nal surface of the capillary remains intact and provides reliable protection against mechanical damage to the capillary. Moreover, in tube SPME provides a simple, easy, and convenient way to couple SPME to gas as well as to liquid phase separation techniq ues. Figure 1 7 Comparis on SPME fiber with in tube SPME 1.7.2.1 Comparison of fiber SPME and i n tube SPME Although the theory of fiber and in tube SPME methods are similar, the significant difference between these methods is that in fibe r SPME the extraction of

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25 analytes is performed with the coating on the outer surface of the fiber using mechanical agitation of the sample while in tube SPME method uses a sorbent coating on the inner surface of a capillary to perform extraction by a flow though process that involves agitation by sample flow in and out of the extraction capillary. Figure 1 8 illustrates the comparison of extraction process for the transfer of the analytes in fiber SPME and in tube SPME. For in tube SPME, it is necessary to prevent plugging of the extraction capillary and flow lines during extracting process and the particles in the sample matrix must be removed by filtration before extraction. Figure 1 8 Comparison of extraction process for the transfer of the analytes i n fiber SPME and in tube SPME [44]

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26 Both SPME and in tube SPME can be performed as: (a) active (dynamic) and (b) passive (static) mode. T o use in tube SPME i n active mode, the matrix containing the analytes is passed through the extraction capillar y and the analytes are extracted by sorbent coating on the capillary inner walls as sample passes through. To use fiber SPME in active mode, a stir bar is used to agitate the sample, thereby speed ing up the extraction of analytes from sample matrix by the extracting phase coating on the surface of the fiber. In static in tube SPME mode, the capillary is filled with sample matrix and the high affinity of the analytes for the sorbent material serves as the driving force for their extraction. Static fiber SPME is carried out mainly in the headspace mode. I n this case, the fiber and extracting phase resides inside the protective tubing (needle), is not exposed directly to the matrix sample. The extraction occurs through diffusion of the gaseous sample contained in the tubing. The static fiber SPME is suitable for field analysis of gaseous samples. The SPME fiber should be handled carefully, because it is fragile, and the fiber coating can be damaged during insertion and agitation. I n in tube SPME on the other ha nd, the protective polyimide coating on the external surface of the capillary remains intact and provides reliable protection against mechanical damage to the capillary. Therefore in tube SPME provides safe and convenient way to couple SPME to gas as well as to liquid phase separation techniques. The introduction of in tube SPME was primarily for coupling SPME to high performance liquid chromatography (HPLC) for automated applications. For fiber SPME HPLC, analysts are currently limited to performing manua l extractions and

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27 desorptions. Analytes extracted by fiber SPME must be desorbed into a suitable receiving solvent prior to HPLC analysis with the help of a SPME HPLC interface constructed with a special desorption chamber and switching valve. Figure 1 9 i llustrate s the procedure of extraction by fiber SPME and desorption for HPLC. A nalyte s are directly extracted by the fiber coating and then introduced to the chromatography is system for further analysis The extraction is carried out by exposure of the SP ME fiber in the headspace or in the sample solution. An SPME HPLC interface (Figure 1 9) equipped with a special desorption chamber is utilized for solvent desorption prior to HPLC analysis. The analytes extracted in the fiber are released in the desorptio n chamber by external addition of solvent or mobile phase, and then introduced to the HPLC column. SPME HPLC ( MS) has been applied to the analysis of various polar compounds such as drugs and pesticides, and has been reviewed [44] However, for automated extraction and analysis, in tube SPME is relatively simple to implement, and it can continuously perform extraction, desorption, and injection using a conventional autosampler without any special SPME HPLC interface for the desorption of analytes. A schema tic diagram of the automated in tube SPME LC system is illustrated in Figure 1 10. For in tube SPME system, the extraction is completed by injection syringe that repeatedly draws and ejects sample from the vial under computer control T he analytes partitio n from the sample matrix into the extracting phase coating until equilibrium is reached. Subsequently, the extracted analytes are directly desorbed from the capillary coating by mobile phase flow or by aspirating desorption solvent after switching the six port valve. Therefore, in tube SPME provide s automated

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28 and high precision extraction for HPLC analysis by setting sample to autosampler. The application of in tube SPME technique to the determination of pesticides, environmental pollutants, drugs, and food contaminants by hyphenation with HPLC, LC MS has been reviewed [44] Figure 1 9 I llustra tion of the extraction procedure of extraction by fiber SPME and analyte desorption for HPLC analysis [44]

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29 Figure 1 10 Schematic diagrams of in tub e SPME LC MS systems [ 44] Both SPME and in tube SPME are also compatible with GC. For fiber SPME GC, the extraction procedure includes [71] : (1) p iec ing the septum of sample container using the needle of SPME device (2) e xpos ing the SPME fiber to the sample and perform extraction either by direction immersion or in the headspace (3) r etract ing fiber back into the needle and withdraw needle. The extracted analytes are thermally desorbed in the GC injection port for further transport into the GC column by the carrier gas. For in tube SPME GC, the capillary with the extracted analytes i s connected to the inlet end of the GC column using a two way press fit fused silica connector housed inside the GC injection port [69] or by placing inside needle c apillary adsorption trap (INCAT) device [72]

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30 1.7.2. 2 Theoretical a spect of in tube SPME The fundamental thermodynamic principle to all extraction techniques commonly involves distribution of analyte between sample matrix and the extracti ng phase. When a liquid is used as the extracting phase, then the distribution constant K es defines the equilibrium conditions and enrichment factors achievable in the technique. The partitioning is between aqueous sample matrix and organic extraction phase, which is il lus trated in Figure 1 11. Figure 1 11 Distribution of analyte between sample matrix and the extraction phase [19] W hen a liquid is used as an extracting phase, the distribution constant K es can be expressed as: (1 4 ) Where, K es : analyte distribution constant between liquid extracting phase and sample matrix,

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31 a e : activit y of an analyte in the liquid extracting phase, a s : activit y of an analyt e in the sa mple matrix, C e : analyt e concentration in the liquid extracting phase, C s : analyte concentration in the sample matrix. In tube SPME uses a flow through system where solid phase is located on the inner surface of capillary and is used as extracting phase When a solid phase is used as the extracting phase a similar equation will be expressed [19] : (1 5) Where, K s es: analyte distribution constant between soli d extracting phase and sample matrix, S e: surface concentration of adsorbed analyte s in the solid extracting phase For the in tube SPME using flow through technique system, the minimum extraction time at equilibrium condition can be expressed [ 19 ] : (1 6 ) Where L is the length of the capilla ry holding the extraction phase V e is the vo lume of the extracting phase V v is the void volume of the capillary,

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32 u is linear flow rate of the sample From the above equation, it can be seen that the extracti ng time is proportional to the length of the capillary and inversely proportional to the linear flow rate of the sample. Extraction time increases wi th an increase in the distribution constant between extrac ti ng phase and sample matrix. Extraction time also increases with the volume of the extracting phase (V e ) but decrease s with an increase of the void volume of the capillary. In another word, under a certain distribution constant, thinner coating with bigge r capillary void volume, less length of capillary and higher linear flow rate will help to fasten the extraction equilibrium, therefore the extraction time can be reduced. It should be emphasized that the above equation can be used only for direct extracti on when the sample matrix passes through capillary [19] 1.7.2.3 Parameters influenc ing in tube SPME In tube SPME is an extraction method based on the transfer of analyte from the sample to sorbent coating in accordance with the analyte distribution betwe en the two phases To obtain rapid and high efficiency of extraction, the following parameters influencing in tube SPME should be considered: (1) the selection of capillary coating (2) sample solution (3) volume of draw/eject cycles and, (4) desorption of compounds from capillary. 1.7.3 Stir bar sorptive extraction (SBSE) Stir bar sorptive extraction (SBSE) is another sorptive technique which can overcomes the limitations of traditional SPME fibers. The theory of SBSE is rather straightforward and similar to that of SPME [73] which is based on distribution between

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33 the sample and the extracting phase and the phase ratio S tir bar sorptive extraction was developed and used for the determination of volatile and semivolatile organic compounds [73 75] In SBSE the coating covers a magnetic stir bar, varying in length from 1 to 4 cm, coated with a relatively thick layer of PDMS (03. 1 mm), resulting in PDMS volumes varying from 55 to 220 u L [74] ( Figure 1 12) This allows for a n extracting phase volume 50 250 t imes greater than that of SPME fibers [76] The coated stir bar is added to an aqueous sample for stirring and extraction. After a certain stirring time, the bar is removed from the aqueous sample, and the sample is thermally desorbed by loading the stir b ar into the injection port of a gas chromatograph y Figure 1 12 Schematic of a stir bar of SBSE [71] The extract ing phase on the stir bar in SBSE is critical for performances of both extraction and thermal desorption. However, the onl y commercially available phase for SBSE is PDMS, marketed by Gerstel. A stir bar ha s three essential parts [76] The innermost part is a magnetic stirring rod, which is necessary for transferring the rotating movement of a stirring plate to the liquid samp le. The second part is a thin glass jacket

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34 that covers the magnetic stirring rod. The outermost part is the layer of PDMS sorbent into which the analytes are extracted. The glass layer is essential for the construction of a high quality stir bar as it effe ctively prevents the decomposition of the PDMS layer due to catalytic effects of the metals in the magnetic stirring rod. 1.8 Reference s for c hapter o ne [1] C. W. Huck, G. K. Boun, J. Chromatogr. A 885 (2000) 51. [2] D. N oble, Anal. Chem. 65 (1993) 693 A. [3] F. Soxhlet, Dingers Polytech J. 232 (1879) 461. [4] J. R. Dean, Extraction met hods for environmental analysis John Wiley & Sons C hichester 1998. [5] A.J. Holden, in Extraction Methods in Organic Analysis, A. J. Handley, Editor, Sheffield Acade mic Press, Sheffield, 1999, 5 [6] S. Pedersen Bjergaard, K. E. Rasmussen, T. Grnhaug Halvorsen, J Chromatogr A 902 (2000) 91. [7] G. Matz, G. Kibelka, J. Dahl, F. Lennemann, J. Chromatogr. A 830 (1999) 365. [8] C. Gerbersmann, R. Lobinski, F. C. Adam s, Anal. Chim. Acta 316 (1995) 93. [9] C. Goncalves, J. J. Carvalho, M. A. Azenha, M. F. Alpendurada, J. Chromatogr. A 1110 (2006) 6. [10] I. J. Barnabas, J. R. Dean, S. M. Hitchen, S. P. Owen, Anal Chim Acta 291 (1994) 261. [11] V. G. Zuin, J. H. Yariw ake, C. Bicchi, J C hromatogr A 985 (2003) 159. [12] J. A. Jnsson, L. Mathiasson, Adv. Chromatogr. 41 (2001) 53. [13] J. A. Jnsson, L. Mathiasson, J. Sep. Sci. 24 (2001) 495. [14] I. Liska, J. Chromatogr. A 885 (2000) 3.

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35 [15] C. F. Poole, A. D. Gunati llekam, R. Sethuraman, J. Chromatogr. A 885 (2000) 17. [16] J. S. Fritz, Analytical Solid Phase Extraction, Wiley VCH, NY 1999. [ 17] N. J. K. Simpson, (Ed.), Solid Phase Extraction. Principles, Techniques and Appli cations, Marcel Dekker, NY 2000. [ 18] J. Pawliszyn, Trends Anal.Chem. 14 (1995) 113. [19] J. Pawliszyn, Sampling and sample preparation for field and laboratory, Elsevier, Amsterdam, 2002 [20] R. M. Smith, J. Chromatogr. A 856 (1999) 83. [21] S M. Wang, Y C. Ling and Y S. Giang, Forens ic Sci. J. 2 (2003) 5. [22] M. A. McHugh V. J. Krukonis, Supercritical Fluid Extraction: Principles and Practice (2nd ed.), Butterworths, London, 1986. [23] M. D. L uque de Castro, M. Valarcel M. T. Tena, Analytical Supercritical Fluid Extraction, Sprin ger, Berlin, 1994. [24] R. M. Smith, J. Chromatogr. A 856 (1999) 83. [25] J. . Jnsson L. Mathiasson. Trends Anal. Chem. 18 (1999) 318. [26] G. A. Audunsson. Anal. Chem 58 ( 1986), 2714 [27] R. P. Belardi, J. Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179. [28] J. Krutz, S. A. Senseman, A. S. Sciumbato, J. Chromatogr. A 999 (2003) 103. [29] B. Zygmunt, A. Jastrzbska, J. Naminesnik, Crit. Rev. Anal. Chem. 31 (2001) 1. [30] F. Alpendurada, J. Chromatogr. A 889 (2000) 3. [31] S. Ulrich, J. Chroma togr. A 902 (2000) 167. [32] G. A. Mills; V. Walker J. Chromatogr. A 902 (2000) 267. [33] F. Augusto, A. L. P. Valente, Trends Anal. Chem. 21 (2002) 428. [34] H. Kataoka, H. L. Lord, J. J. Pawliszyn, Chromatogr. A. 880 (2000) 35. [35] T. Kumazawa, X. P Lee, K. Sato, O. Suzuki, Anal. Chim. Acta 492 (2003) 49.

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36 [36] H. Kataoka, Trends Anal. Chem. 22 (2003) 232. [37] X P. Lee, T. Kumazawa, K. Sato, O. Suzuki, Chromatographia 42 (1996) 135 [38] G. Bentivenga, M. D'Auria, P. Fedeli, G.. Mauriello, R. Rac ioppi, Int. J. Food Sci. Technol. 39 (2004) 1079. [39] K. Fytianos, N. Raikos, G.. Theodoridis, Z. Velinova, H. Tsoukali, Chemosphere 65 (2006) 2090. [40] Y. Fan, Y. Q. Feng, J. T. Zhang, S. L. Da, M. Zhang, J. Chromatogr. A 1074 (2005) 9. [4 1] Z. Liu, J. Pawliszyn, J. Chromatogr. Sci. 44 (2006) 366. [42] C. Peres, C. Viallon, J. L. Berdague, Anal. Chem. 73 ( 2001 ) 1030 [43] S. A. S. Wercinski, Solid Phase Microextraction: A Practical Guide, Marcel Dekker, Inc, NY 1999 [44] H. Kataoka, Anal Bioanal Chem 373 (2002) 31 [45] J. Pawliszyn, Solid Phase Microextraction: Theory and Practice, Wiley VCH NY 1997 [46] D. Louch, S. Motlagh, J. Pawliszyn. Anal. Chem. 64 (1992) 1187. [47] C. L. Arthur, L. M. Killam, K. D. Buchholz, J. Pawliszyn, J. R. Berg, Anal. Chem. 64 (1992) 1960. [48] Z. Zhang, J. Pawliszyn, Anal. Chem. 65 (1993) 1843. [49] G. Vas, K. Vekey, J. Mass Spectrum. 39 (2004) 233. [50] K. D. Buchholz, J. Pawliszyn, Anal. Chem. 66 (1994) 160. [51] C. L. Arthur, J. Pawliszyn, Anal. Chem. 62 (1990) 2145. [52] K. D. Buchholz, J. Pawliszyn, Environ. Sci. Technol. 27 (1993) 2844. [53] Application Note 17 Supelco, Bellefonte, PA. USA [54] B. J. Hall, J. S. Brodbelt, J. Chromatogr. A 777 (1997) 275.

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37 [55] O. E. Mills, A. J. Broome, ACS Symp. Se r. 705 (1998) 85. [56] V. Mani In: J. Pawliszyn, (Ed.), Applications of Solid Phase Microextraction, Royal Society of Chemistry (RSC), Cambridge, UK, 1999, 57. [57] E. Turiel, J. L. Tadeo, A. Martin Esteban, Anal. Chem. 79 (2007) 3099. [58] C H. Xiao, S Q. Han, Z Y. Wang, J. Xing, C Y. Wu, J. Chromatogr. A 927 (2001) 121. [59] J X. Yu, D. Li, C Y. Wu, L. Wu, J. Xing, J. Chromatogr. A 978 (2002) 37. [60] Z R. Zeng, W L. Qiu, Z F. Huang, Anal. Chem. 73 (2001) 2429. [61] D H. Wang, J. Xing, J G. Peng, C Y. Wu, J. Chromatogr. A 1005 (2003) 1. [62] X J. Li, Z R. Zeng, S Z. Gao, H B. Li, J. Chromatogr. A 1023 (2004) 15. [63] C. Dietz, J. Sanz, C. C mara, J. Chromatogr., A 1103 (2006) 183. [64] S. L. Chong, D. Wang, J. D. Hayes, B. W. Wilhite A. Malik, Anal. Chem. 69 (1997 ) 3889 [65] F. Guo, T. Gorecki, D. Irish J. Pawliszyn, Anal. Commun. 33 (1996 ) 361 [66] A. Mohammadi, Y. Yamini N. Alizadeh, J. Chromatogr. A 1063 (2005 ) 1 [67] M. Farajzadeh N.A. Rahmani, Anal. Sci. 20 (2004) 1359 [6 8 ] R. Eisert, J. Pawliszyn, Anal. Chem. 69 (1997) 3140. [6 9 ] S. Bigham, J. Medlar, A. Kabir, C. Shende, A.; Alli, A. Malik Anal. Chem. 74 (2002) 752. [ 70 ] J. V. Hinshaw, LC GC Europe 16 (2003) 803. [7 1 ] Supelco bulletin 928 Bellefonte, PA. USA [7 2 ] M. E. McComb, R. D. Oleschuk, E. Giller, H. D. Gesser, Talanta 44 (1997) 2137 [7 3 ] E. Baltussen, P. Sandra, F. David C. Cramers, J. Microcol umn Sep. 11 (1999) 737. [7 4 ] J. Ver cauteren, C. Peres, C. Devos, P. Sandra, F. Vanhaecke and L. Moens, Anal. Chem. 73 (2001) 1509.

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38 [7 5 ] P. Popp, C. Bauer L. Wennrich, Anal. Chim. Acta 436 (2001) 1. [7 6 ] M. Kawaguchi, R. Ito, K. Saito, H. Nakazawa, J. Pharm. Biomed. Anal. 40 (2006) 500.

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39 CHAPTER TWO SOLID PHASE MICROEXTRACTION AND SOL GEL TECHNOLOGY 2.1 Introduction to sol gel process and some basic definitions Generally, the sol gel process involves the transition of a system from a liquid "sol" (mostly col The starting materials used in the such as metal alkoxides. Typically, in sol gel process the precursor is subjected to a series of hyd rolysis and polymerization reactions to form a colloidal suspension, or a Further drying and heat If the liquid in a wet Here are some terms that need to be defined [1]. A colloid is a suspension in which the dispersed phase is so small (~ 1 100 0 nm) that the gravitational forces are negligible and interactions are dominated by short range forces, such as van der Waals attraction and surface charges. The inertia of the disperse phase is small enough to exhibit Brownian motion, a random walk drive by momentum imparted by collision with molecules of the suspending medium. A sol is a colloidal suspension of solid particles in a liquid. An aerosol is a colloidal suspension of particles in a gas. In sol gel process, the precursors (starting compounds) for preparation of a colloid consist of a metal or metalloid element surrounded by various ligands

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40 (appendage not including another metal or metalloid atom). Metal alkoxides are popular precursors because they react readily with water. The reaction is call ed hydrolysis. Two partially hydrolyzed molecules can link together, which is called condensation reaction. Condensation liberates a small molecule, such as water or alcohol. This type of reaction can continue to build larger and larger silicon containing molecules by the process of polymerization. Applying the sol gel process, it is possible to fabricate ceramic or glass materials in a wide variety of forms: ultra fine or spherical particles in the form of powders [2], thin film coatings [3], ceramic fibe rs [4], microporous inorganic membranes [5], monolithic ceramics and glasses, or extremely porous aerogel materials etc. Sol gel technology has found interesting applications in development of new materials for catalysis [6, 7], chemical sensors [8, 9], m embrane [10], fibers [11], optical gain media [12], photochromic and nonlinear applications [13, 14], solid state electrochemical devices [15], nuclear industry [16], and electronic industry [17] in various scientific and engineering fields. A simple overv iew of the sol gel process is graphically presented in Figure 2.1.

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41 Figure 2.1 Overview of the sol ge l process. Adapted from [1, 18]

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42 2.2 Historical background of sol gel technology Sol gel research on ceramic and glass materials can be traced back to the mid 1800s when Ebelmen [19] found that solutions of certain compounds gelled on exposure to atmosphere. However, these materials presented interest only to chemists. It was finally in the 1930s, that systematic improvement of sol gel technology was ca rried out by Geffcken and Dislich of Schott Glass Company in Germany [20]. The network structure of silica gels was widely accepted in the 1930s when Hurd [21] showed that they must consist of a polymeric skeleton of silicic acid enclosing a continuous liq uid phase. In the 1950s, the method for the preparation of homogeneous powder was popularized by Roy in ceramics research [22, 23]. However, that work was not directed toward an understanding of sol gel reaction mechanism. In 1970s, controlled hydrolysis a nd condensation of alkoxides for preparation of multicomponent glasses was independently developed by Levene and Thomas [24] and Dislich [25] due to an increased interest from ceramics industry. Tremendous attentions in sol gel research have been obtained ever since Yoldas [26] and Yamane et al. [27] showed that large monoliths could be made by the sol gel method through the careful drying of gels in the 1980s. In 1987, Cortes et al. [28] prepared sol gel monolithic ceramic beds within small diameter capi llaries as separation columns in liquid chromatography (LC). In 1993, Crego et al. [29] prepared a thin layer of silica gel with chemically bonded C 18 moieties on the inner walls of fused silica capillaries for use in reversed phase HPLC. Guo and Colon [30 ] used a similar sol gel technology to prepare stationary phase coatings for open tubular LC and electrochromatography. Malik and co workers introduced sol gel

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43 coated columns for capillary GC [31], sol gel coated fibers for solid phase microextraction (SPM E) [32] and in tube SPME [33]. Gbatu [34] also prepared SPME fiber with sol gel technology. These preceding works led to sol gel research aiming at developing novel sorbent materials for solid phase microextraction [35 39] and solid phase extraction [40 43 ]. 2.3 The potential of sol gel chemistry in coat ing technology for analytical m i croextraction 2.3.1 Problems with tra ditional SPME coating technology In chapter one, some drawbacks of fiber SPME inherited from physical construction of SPME device such as the breakage of the fiber and bending of needles were pointed out. The introduction of an alternative format of SPME seems to be a promising direction in solving those problems. The other drawbacks arise from the traditional coatings and coating technol ogy [44]. First, the traditional SPME coatings are designed to extract either polar or non polar analytes for a given matrix. It is important to have a sorbent that can extract both polar and non polar compounds with high extraction sensitivity needed for trace analysis. Second, in traditional SPME only a short length of the fiber is coated with sorbent. The short length of the fiber coated with sorbent translates into low sorbent loading which in turn leads to low sample capacity, which significantly limit s the sensitivity of traditional SPME coating. This is particularly important for analyzing ultra trace contaminants. Increasing the coating thickness [45, 46] seems one possible way of improving extraction sensitivity. However, the increased coating thick ness requires longer equilibrium time, which translates into a long analysis

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44 time. Moreover, immobilization of thicker coating on fused silica surface is difficult to achieve by conventional approaches [47, 48]. Therefore, developing an effective alternati ve approach to immobilize thick coatings is important for reliable and effective SPME performance. Third, low thermal and solvent stability of traditional SPME coatings represents a major drawback of conventional SPME technology. In traditional approaches, relatively thin coatings can be immobilized on the capillary inner surface though free radical cross linking reactions [49, 50]. Because of the absence of direct chemical bonding between the coating and the substrate, the thermal and solvent stabilities o f such coatings are typically poor. The problem is more severe in the case of thicker coatings. When coupled to GC, such extracting coatings may cause reduced thermal stability of conventional coatings leads to incomplete sample desorption and sample carry over problems. Low solvent stability of conventionally prepared extraction coatings presents an obstacle to the hyphenation of in tube SPME with liquid phase separation techniques because HPLC employs organic mobile phase systems for desorption of analytes Evidently, all above problems are related to coating materials and coating technology. Novel approaches to sorbent chemistry and coating technology are very important for solving these problems. Development of new methods for the preparing of chemically immobilized coatings form advanced material systems to achieve desired selectivity and performance in SPME is an important direction in SPME research. 2.3.2 The advantages sol gel technology for use in analytical microextraction Sol gel technology is one a pproach to address most of the above mentioned problems through the creation of chemically bonded sorbent coatings [31 33, 51].

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45 S ol gel chemistry provides a simple and convenient pathway to synthesize advanced material systems that can be used to prepare s urface coatings. The advantages sol gel technology in the area of fiber based SPME or capillary based SPME (CME) are as follows [44, 52]: (1) it combines surface treatment, deactivation, coating, and sorbent immobilization into a single step procedure mak ing the whole SPME fiber/capillary manufacturing process very efficient and cost effective; (2) it creates chemical bonds between the fused silica surface and the created sorbent coating, therefore it can achieve enhanced extracting phase stability (solven t stability and thermal stability) in sample preparation and chromatographic separations (3) it provides surface coatings with high operational stability ensuring reproducible performance of the sorbent coating under operation conditions involving high tem perature and/or organic solvents, and thereby it expands the SPME application range towards both higher boiling as well as thermally labile analytes; (4) it provides the possibility to combine organic and inorganic material properties in extraction sorbent s providing tunable selectivity; (5) it offers the opportunity to create sorbent coatings with a porous structure which significantly increases the surface area of the extracting phase and provides acceptable stationary phase loading and sample capacity us ing thinner coatings; (6) it reaches a better homogeneity from raw material on the molecular level; (7) it provides mild reaction temperature; (8) it provides the possibility to design the material structure and property through proper selection of sol gel precursor and other components; (9) it can easily provide different products such as coatings, and monolithic bed, particles etc

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46 2.4 Fundamentals of sol gel technology To design and create proper sol gel material, understanding the general chemical react ions involved in the sol gel process is very important. Chemical reagents for the preparation of sol gel sorbents normally include (1) sol gel precursor(s); (2) a solvent for dispersing and mixing all the reagents; (3) a polymer which provides selective fu nctional group; (4) deactivating reagents; (5) a catalyst, and (6) water. At least one sol gel precursor is used in sol gel synthesis. Sol gel precursors are usually alkoxide based materials [53]. However, alkoxides of various metals and metalloids (Si, A l, Ti, Zr, Ge, etc. ) [54 59] have been utilized to create sol gel sorbents, and they have been applied in analytical microextraction. Among them, silicon based alkoxides, especially tetraethoxysilane (TEOS) and methyltrimethoxysilane (MTMOS) are the most c ommonly used precursors [60 64]. Conventionally, tetraalkoxysilanes are used as sol gel precursors [65]. However, the use of alkyl or aryl derivatives of tetraalkoxysilanes as precursors may provide important advantages in coating technology because sol ge ls obtained by using these derivatives are reported to be less prone to cracking and shrinking [31, 65]. An organic polymer is usually used to form a network and provide the pendent functional groups for sol gel materials for selective interaction with t he target analytes. The resultant microextraction performance of sol gel stationary phase will mainly be affected by the characteristics of the pendent functional group. They provide the sol gel material with different affinity to certain classes of analyt es based on the structure and polarity of pendent functional groups acquired from the polymer(s). Polysiloxanes are

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47 important SPME coating materials due to its high thermal stability and good film forming characteries. Poly(dimethlysiloxane) (PDMS) has bee n commonly used in sol gel microextraction sorbent either as a mono polymer [54] or co polymers [63]. Hydroxy termanited, PDMS has been used to synthesize sol gel sorbents that have been used in a variety of microextraction applilcation. Other used polymer s such as poly (vinyl alcohol) (PVA) [63], polyethylene glycol (PEG) [66, 67], hydroxyfullerene [68], Ucon [69] and poly (methylphenylvinylsiloxane) (PMPVS) [70] etc. have been used to produce sorbent coatings. All the above mentioned precursors, polymers, and deactivating reagents (if necessary) are dispersed and mixed well in solvent(s). Here the solvent can be a pure organic solvent or a mixture of organic solvents. The purpose of the solvent is usually for the dissolution of all components of sol soluti on to achieve a molecule level uniformity in the mixed system. After mixing, water and a proper catalyst are added to the system to initiate hydrolysis of the precursor(s). The catalysts for sol gel reactions usually include (I) acids [60, 71 72], (II) bas es [73] (III) or ions ( e.g. F ), [74, 75]. A radical initiator is used in conjunction with ultraviolet (UV) light induced polymerization. In sol gel synthesis, trifluoroacetic acid is the most popular catalyst since its initial use in 1997 [31]. It serves not only as a catalyst but also an organic solvent and a source of water (1% water). As a strong organic acid of pKa value of 0.3, it provides for relatively the short gelling times. Other than TFA, HCl is the second most commonly used catalyst for sol ge l reactions [60]. Acid catalyzed sol gel reactions are more popular in the preparation of microextraction sorbents. However,

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48 NaOH, and F are sometimes used for comparison purposes in sol gel CME techniques [76]. Generally, acid catalyzed sol gel processes are believed to produce linear polymers while base catalyzed processes produce highly condensed particulate structures. Acid catalyzed material also has a tendency to be highly porous and possesses higher surface areas in comparison to base catalyzed sol gel materials. High surface area and narrowly distributed pore structure of acid catalyzed sol gel material make them very suitable for being used as sorbent coatings in analytical microextraction. Sol gel synthesis consists of two processes: (1) hydrolys is of the precursor(s) and (2) water or alcohol polycondensation of the sol gel active species present in the sol solution [1]. The sol gel active species include fully or partially hydrolyzed precursors and polymers which include silica based species, ana logous non silica species, silanol group or any other species chemically reactive to them. Scheme 2.1 illustrates hydrolysis and condensation of tetramethoxysilane (TMOS) as an example (Scheme 2.1). During the process, a liquid like colloidal suspension (t he sol) is transformed by hydrolysis. Then a 3 D network, a gel form via polycondensation reactions. In sol gel process, hydrolysis and condensation reactions occur simultaneously not stepwise. A wet three dimensional sol gel network of porous material i s formed as the polycondensation reaction progress es

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49 Scheme 2.1 Illustration of hydrolysis and condensation of tetramethoxysilane (TMOS). Adapted from [18] 2.5 Creation of sol gel CME sorbents Further adva ncements in the area of analytical microextraction are greatly dependent on improvements and new breakthroughs in sorbent development and coating technology to replace traditional coating technology. The development of sol gel coatings and/or monolithic be ds has proved to be an important step in this direction. Generally, preparation of the sol gel stationary phase coatings for CME involves four typical steps: (1) pre treatment of the fused silica capillary, (2) preparation of the sol solution, (3) sol gel coating process, and (4) treatment of coated capillary. 2.5.1 Pre treatment of the fused silica capillary The purposes of capillary pretreatment are: (1) cleaning the possible contaminants inside the fuse silica capillary, (2) increasing the concentration of surface silanol group.

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50 Silanol group concentration on the capillary surface may be low due to the formation of siloxane bridges due to condensation of neighboring silanol groups at high d rawing temperatures (about 2000 C ), and may vary from one piece t o another piece. Since silanol groups on the capillary surface represent the binding sites for in situ created sol gel extracting phases, higher surface concentration of these binding sites is desirable to facilitate the formation of chemical bonds between sol gel extracting phase and the capillary inner surface. Alkali solutions are traditional approaches for pretreatment of fused silica capillaries [77 83]. The pretreatment usually starts with rinsing by 1 M of NaOH, followed by diluted HCl to neutralize excessive NaOH, and rinsing with purified water. After rinsing, the capillary is usually purged with helium or nitrogen. This traditional pretreatment method has been used for prepare sol gel CE preconcentration columns [79], sol gel SPME fibers [11, 35] a nd stir bars for sorptive extraction [77]. It also was used in preparing CME [78, 81 83] sorbents. Hayes and M alik [84, 85] reported the use of hydrothermal treatment of the inner surface of fused silica capillary prior to in situ creation of surface coat ed and monolithic capillaries. This hydrothermal treatment was performed for several reasons. First, the water serves to clean the inner capillary surface, removing any contaminants originating from the capillary drawing process or postdrawing manipulation and handling. Moreover, this pretreatment with water enhances surface silanol concentrations, thereby providing a higher percentage of bonding sites for anchoring the sol gel coating. A homemade gas pressure operated capillary filling/purging device [69] was used to realize this (Figure 2.2). The fused silica capillary was sequentially rinsed with two organic solvents

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51 of different polarities: CH 2 Cl 2 was used first to clean the non polar and moderately polar contaminations inside the capillary. Then CH 3 OH w as used to substitute CH 2 Cl 2 and also to clean the relatively polar contaminations on the inner surface. Deionized water was then passed through the capillary under helium pressure. This was followed by purging of the capillary with helium for 5 min. Both capillary ends were then sealed using an oxyacetylene torch and the capillary was placed in a GC oven at 250 C for thermal conditioning for 2 h. Following this, the capillary was removed from the GC oven, it ends were cut open using an alumina wafer, and the capillary was further purged with helium for an additional 30 min at ambient temperature. Figure 2.2 Homemade capillary filling/purging device Adapted from [69]

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52 2.5.2 Preparation of the sol solution Designing the sol solution is the most critical step in preparing sol gel CME capillary. Judicious selection of the sol solution ingredients is essential for a successful creation of the desired sol gel sorbent. Chemical reagents for the preparation of sol gel sorbents normally includes sol ge l precursor(s), a solvent for dispersing and mix all the reagents, a polymer which provides the functional group deactivation reagent(s), a catalyst (or inhibitor) and water. The role of each ingredient plays has been explained in section 2.4 In addition to typical ingredients in the sol solution, various additives are often used, such as surface deactivating reagents or a drying control chemical additive (DCCA). An important attribute of sol gel for coating technology is the simplified deactivation step compared with traditional coating technology [31]. In sol gel chemistry, deactivation is achieved by adding to the sol solution traditional deactivating reagents such as poly(methylhydrosiloxane) (PMHS), Hexamethyldisilazane (HMDS) etc that contain chemi cally reactive hydrogen atoms. These chemicals are not sol gel reactive but they get physically incorporated in the coating and deactivate residual silanol groups on the created sol gel material during the thermal step. This is in contrast with traditional coating approaches, where silica surface is deactivated prior to coating. Malik and coworkers reported the use of various deactivation reagents for sol gel stationary phases, such as ph enyldimethylsiane (PheDMS) [84, 86] 1,1,1,3,3,3 hexamethyldisilazane (HMDS) [50, 51, 57, 58], and polyethylhydeosiloxane (PMHS) [31, 54]. Some deactivating reagents and deactivation reactions of HMDS are

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53 shown in Scheme 2.2 and Scheme 2.3. A drying control chemical additive (DCCA) such as formamide, glycerin, dimethyl ether and oxalic acid is usually used as a sol solvent and it may play other critical roles in the sol gel reactions [87, 88]. During sol gel process, stress may be developed in the sol gel network as the solvent escapes or as the pore size changes during thes e processes. This stress may cause problems during the formation of the uniform sol gel coatings. To overcome this problem, DCCA is incorporated in the starting mixture of sol solution, and they can release the capillary stress generated during of the coat ed surface [1, 77, 89, 90]. Unfortunately, the exact way in which the DCCA improves the drying process is still unclear [90]. Scheme 2.2 Deactivating reagents

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54 Scheme 2.3 Deactivation of silica surfa ce with HMDS The homogeneity of the sol is very important. Therefore careful selection of a solvent system which is compatible with other ingredients is necessary. A mixture of solvents compatible with inorganic and organic components in the sol s ystem needs to be used to achieve the homogeneity. The viscosity of the system is another important parameter for in tube SPME coatings. The water/precursors ratio in the sol solution also affects the speed of reaction as well as the physical properties of the obtained sol gel materials. The ratio should be carefully controlled to adjust the reaction speed and to fine tune structures of sol gel materials.

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55 2.5.3 Sol gel coating process After preparing sol solution, the sol solution was filled into the capil laries. Sol solution was kept inside of the capillary for a controlled period of time to facilitate the formation of sol gel reactions inside the capillary. During this process, the evolving sol gel organic inorganic hybrid material gets chemically bonded to the inner walls of the capillary via condensation with the surface silanol groups. After this, the unbonded portion of the sol solution is expelled from the capillaries under inert gas leaving behind a surface bonded sol gel thin coating within the capi llary. In the end, this thin coating is further purged with inert gas for an additional period to facilitate the evaporation of the remaining volatile organic solvents. The in capillary residence time of the sol solution is various and it can be adjusted f or application purpose. It can be adjusted to prepare sol gel coatings with various thicknesses. A sol gel in tube SPME coating technology was first introduced by Malik and co workers [69]. A homemade capillary filling/purging device (Figure 2.2) was used to fill the capillary with the coating sol solution under helium. Then an additional period of purging of helium was applied to facilitate the evaporation of the remaining organic solvents. Hu and coworkers [78, 81] used a syringe to introduce sol solutio ns into the capillary to prepare CME sorbents followed by purging nitrogen to remove the sol solution. 2.5.4 Further treatment of sol gel coated CME capillary After coating, the capillary is further thermally treated for aging, drying, conditioning and cl eaning. Different temperature programs have be been developed to

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56 achieve the desired performance. Malik and coworkers [31, 57] installed the capillary in a GC oven using a temperature program of 40 to 300 C or even higher at a rate of 1 C/min under the p urging of helium. Purging with inert gas helped to remove the solvent and unbonded materials from the coating at high temperature. The prepared CME capillary was coupled with both GC and HPLC [44, 47]. Hu and coworkers [81] connected CME capillary in a GC oven under nitrogen, the solvent was removed through the capillary at 1 bar for 10 min and then at 0.2 bar for 60 min to prepare a zirconia coating, then heated at 573 K for 8 h in a muffle furnace. The prepared zirconia coating was used for on line hyphen ation with ICP MS. In prepare another N (2 aminoethyl) 3 aminopropyltrimethoxysilane (AAPTS) silica coating for on line hyphenation with Inductively Coupled Plasma Mass Spectrometry (ICP MS), they also placed the capillary in a muffle furnace at 120 C fo r 8 h with the heating program of 1 C min 1 rising from the ambient temperature for the formation of the coating. When making a monolithic column for CME, Hu and coworkers [78] sealed both ends of the capillary with silicon rubber followed by further reaction at 40 C for 12 h. The prepared monol ithic column was for on line CME coupled to HPLC. In the end, the CME capillary was rinsed with ethanol in order to remove the surfactant [78] or template materials [91]. 2.6 Charac terization of sol gel extracting phase and its morphology Various charact erization methods are employed to understand sol gel coatings. Scanning electron microscopy (SEM) is one of the most popular techniques to evaluate the morphology of sol gel coatings thanks to its combination of higher magnification,

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57 larger depth of focus, greater resolution, and ease of sample observation [92]. SEM can reveal the uniformity of the coating thickness and structural details or defects through cross sectional and surface views of sol gel coatings. In addition to SEM, Infrared (IR) spectroscopy is also an important and simple tool to follow the evolution of the sol gel material and microstructure of sol gel silica films [93, 94]. FTIR spectroscopy is most commonly used for identifying specific chemical bonds on the sol gel sorbent coating. Besid es IR, various techniques such as mass spectrometry (MS), fluorescence microscopy and nuclear magnetic resonance (NMR) have been used to study chemical bonds in sol gel structure [95, 96]. NMR is another important and powerful analytical technique to inves tigate the structural features for sol gel material. NMR, SEM and FTIR are the most frequently used techniques to study gel formation and for surface coating characterization. Other techniques atomic force microscopy (AFM) [97], small angel X ray photoelec tron spectroscopy (XPS) [98], etc. are also used to study the morphology of sol gel materials 2.7 Reported sol gel coating materials in SPME and CME Sol gel chemistry provides a simple and convenient pathway to synthesis advanced coating materials for fib er based SPME or capillary SPME (CME). Various types of polymers and functionalized organic compounds have been used. Table 2.1 summarized polymer and organic components that have been used to prepare sorbents in the area of SPME and CME in recent years.

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58 Table 2.1 O rganic sorbents and their applications. Adapted from ref [99] Name of the stationary phase Functional Group or Repeating Functional Group structure SPME Techniques Ref. Polyvinyl chloride (PVC) HP SPME [100 102] Poly(ethylene glycol) (PEG) SPME CME [103 105] Poly(ethylenepropylene glycol) monobutyl ether (Ucon) SPME [104] 3 Aminopropyltrimetho xysilane (APTMS) SPME, CME [59, 106] N (2 aminoethyl) 3 ami nopropyltrimethoxysilan e (AAPTS) CME, Monolithic CME [91,107] Hydroxy terminated polydimethylsiloxane (PDMS) HS SPME SPME CME [32,59, 1 05, 108] Hydroxy terminated polymethylphenylsiloxa ne (PMPS) SPME CME [109 111]

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59 Table 2.1 (Continued) Polyacrylate (PA) SPME [112] Divinyl benzene (DVB) HS SPME [113] Calixarenes HS SPME [114 118] cyclodextrins HS SPME [119 123] Poly(trifluoropropyl)me thylsiloxane (PTFPMS) HS SPME [124] Poly(butylacrylate) SPME [125]

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60 Table 2.1 (Continued) Methyl acrylate (MA) HS SPME [126] Methyl methacrylate (MMA) HS SPME [126] Butyl meth acrylate (BMA) HS SPME [126 128] Anilinemethyltriethoxys ilane (AMTEOS) SPME [129] Crown Ethers SPME [11, 130 132] Calixcrowns S PME [35, 133]

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61 Table 2.1 (Continued) Poly(methylphenylvinyl siloxane) CME, HS SPME [37, 134] Methyl groups CME [135] Cyano Polydimethylsilo xane CME [67] Polytetrahy drofuran (poly THF) CME [44] n Octyltriethoxysilane (C 8 TEOS) Monolithic CME [78] Dendrimers CME [51] Hydroxyfullerene (fullerol) OH TSO HS SPME [68] Poly(vinyl alcohol) HS SPME [63, 136]

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62 2.8 Drawbacks of silica based sol gel materials Sol gel microextraction sorbents reported so far are predominantly silica based. Despite many attractive material properti es such as mechanical strength, surface characteristics, catalytic inertness, surface derivatization possibilities, etc., silica based sol gel materials have some inherent shortcomings. The main shortcoming of silica based sorbents is the narrow range of p H stability. Siloxane bond (Si O Si) on the silica surface hydrolyzes at pH > 8 [137] and it happens rapidly under elevated temperatures [138]. Under acidic conditions, siloxane bond is also unstable [139], and it gets worse with elevated temperatures [140 141]. A number of methods such as multiple covalent bonds [142], multi dentate synthetic approach [143], and end capping [144] have been used to solve this problem. None of them, however, seems to work effectively. Therefore, developing sorbents with a w ide range of pH stability is fundamentally important for chromatographic separation and sample preparation technology. From this point of view, metal oxides such as zirconia, titania, and alumina are interesting materials to offer better chemical and therm al stabilities [138]. Due to these advantages, they have attracted attention of separation scientists and they have been used in chromatography for many years. 2.9 S ol gel process using transition metal alkoxide Transition metal alkoxides, M (OR) z (M is Ti, Zr, and Hf etc. ) are used sol gel precursors to glasses and ceramics. These transitional metal alkoxides are distinguished from silicon alkoxides (Si(OR) 4 ) in two aspects [1]: (1) they have greater chemical

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63 reactivity resulting from the lower electron egativity of transition elements, which causes them to be more electrophilic and thus less stable toward hydrolysis, (2) they have the ability to exhibit several coordination states, so that coordination expansion occurs spontaneously when water or other n ucleophilic reagents are added, and they are able to expand their coordination via olation, oxolation, alkoxy bridging, or other nucleophilic association mechanisms, (3) the greater reactivity of transition metal alkoxides requires that they be processed w ith stricter control of moisture and conditions of hydrolysis in order to prepare homogeneous gels rather than precipitates, (4) the generally rapid kinetics of nucleophilic reactions cause fundamental studies of hydrolysis and condensation of transition m etal alkoxides to be much more difficult than for Si(OR) 4 Similar to silicon alkoxides (Si(OR) 4 ), two main reactions typically are involved in the sol gel process including transition metal alkoxides: (1) hydrolysis and (2) water or alcohol condensation reactions. The general scheme for sol gel hydrolysis and condensation reactions of metal alkoxide precursors are illustrated in Scheme 2.4. For coordinatively saturated metals in the absence of catalysts, hydrolysis and condensation both o ccur by nucleophilic substitution (S N ) mechanism involving nucleophilic addition (A N ) followed by proton transfer from the attacking molecule to an alkoxide or hydroxo ligand within the transition state and removal of protonated species as either alcohol o r water. The condensation process by removal of alcohol molecule is called alcoxolation, and that by removal of water molecule is called oxolation. Scheme 2.5 illustrates the mechanism for hydrolysis, alcoxolation, oxolation or olation [1].

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64 (A) Hydrolysis (B) Water condensation ( C) Alcohol condensation Scheme 2.4 General sol gel process for transitional metal alkoxides. Adapted from [ 1, 145]

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65 (A) Hydrolysis (B) Oxolation (C) Alcoxolation (D) Olation Scheme 2.5 Mechanisms of sol gel hydrolysis and condensation reactions o f metal alkoxides [1]

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66 In hydrolysis, the first step (a) for hydrolysis is a nucleophilic addition, which leads to a transition state (b), where the coordination number of metal atom has increased by one. The second step involves a proton transfer within (b ) leading to the intermediate (c). The third step is the departure of the leaving group which should be the most positively charged species within the transition state. The entire process, (a) to (d) follows a nucleophilic substitution mechanism. The oxol metal atoms through the elimination of a water molecule. Basically, oxolation follows the same mechanism as that for condensation process: the metal atom replacing hydrogen atom in the ente ring group. When the metal is unsaturated in terms of coordination number, oxolation occurs by A N with rapid kinetics. Alcoxolation follows pretty much the same mechanism as oxolation except the leaving group is an alcohol molecule. Alcoxolation and oxolat ion are two competitive processes. The thermodynamics of hydrolysis, alcoxolation, and oxolation are governed by the strength of the entering nucleophile, the electrophilicity of the metal, and the partial charge and the stability of the leaving group. In addition, condensation can also occur by olation when the transfer ability of the proton is large. The thermodynamics of olation depend on the strength of the entering nucleophile and the electrophilicity of the metal. The kinetics of the olation are syst ematically fast because there is no proton transfer in the transition state. Acid or base catalyst can influence both the hydrolysis and condensation rates and the structure of the condensed product. Acids serve to protonate alkoxide groups, enhancing the reaction kinetics by producing good leaving group, and eliminating the

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67 requirement for proton transfer within the transition sate. Hydrolysis goes to completion when sufficient water is added. 2.10 Non silica sol gel materials in analytical microextractio n and chromatographic separation Metal oxides such as zirconia, titania and alumina offer much better chemical stability than silica which has attracted a great deal of interest in the separation science community [138]. They have been used in chromatogra phy for many years. The literature shows that zirconia has been the most systematically studied transition metal oxide. Zirconia appears possess thermal exceptionally high stability. It has been extensively for capturing and storing radiochemical wastes. Zirconia possesses superior alkali resistance than other metal oxides, such as alumina, silica and titania [2] [138]. It is practically insoluble within a wide pH range (1 14) [ 146 148]. Zirconia also shows outstanding resistance to dissolution at high te mperatures [149]. Besides the extraordinary pH stability, excellent chemical inertness and high mechanical strength are two other attractive features that add value to zirconia as a support material in chromatography and membrane based separations. Extensi ve research has been done on zirconia particles and their surface modifications for use as HPLC stationary phase [150, 151]. A number of reports have also recently appeared in the literature on the use of zirconia modified fused silica capillary electropho resis (CE) [152, 153]. A zirconia based hybrid organic inorgnic sol gel polydimethyldiphenylsiloxane (PDMDPS) coating was developed for CME [58]. The sol gel zirconia PDMDPS coating was immobilized on the inner surface of a fused silica microextraction cap illary. The resultant CME coating

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68 efficiently extracted polycyclic aromatic hydrocarbons, ketones, and aldehydes from aqueous samples, and it performance remained practically unchanged even after continuous rinsing with a 0.1 M NaOH solution for 24 h. Rece ntly, a zirconia hollow fiber was prepared by sol gel technology and applied in microextraction [56]. For this, a polypropylene hollow fiber was employed as the template, and it was immersed in the proper zirconia sol precursor for specify followed by a dr ying process. After burning the template off, the zirconia hollow fiber was obtained. The zirconia hollow fiber is similar to its propylene hollow fiber template in terms of morphology. However, it exhibits a bimodal porous structure consisting of: through pores and skeleton mesopores. The pore structure and wall thickness can be easily controlled during the coating process and heat treatment. The zirconia hollow fiber was a highly selective for phosphonic acid containing compounds. Pinacolyl methylphospho nic acid is a nerve agent degradation product and it was used as a model analyte. Titania has also attracted interest recently in separation science due to its superior pH stability and mechanical strength compared with silica [154 157] Several studies h ave been conducted on the application of titania in chromatographic separations [156 161] A sol gel titania poly(dimethylsiloxane) (TiO 2 PDMS) coating was successfully developed for capillary microextraction (CME) by Malik and coworkers in 2004 [57]. This is the first report of the use of sol gel titania based organic inorganic material as a sorbent in capillary microextraction. The sol gel titania PDMS coating was immobilized on the inner surface of a fused silica capillary. It showed good affinity for ma ny non polar and moderately polar compounds, and it was used for on line extraction

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69 in hyphenation with HPLC analysis of polycyclic aromatic hydrocarbons, ketones, and alkylbenzenes. This newly developed coating demonstrated excellent pH stability. Extract ion characteristics remained unchanged after continuous rinsing with a 0.2 M NaOH solution for 12 hours. Besides those neutral compounds, Zeng and coworkers utilized sol gel titania in conjunction with hydroxy terminated silicone oil as a sorptive coating for SPME fibers [162] The sol gel coating provided significant extraction and had sensitivity to polar compounds in SPME GC analysis [162]. The application demonstrated extraction and analysis of six aromatic amines in dye process wastewater. The develope d sol gel hybrid titania coating was extremely pH stable, and its extraction characteristic remained unchanged after rinsing with a 3 M HCl or NaOH solution for 12 hours. The thermal stability of this coating was as high as 320 C. An ordered, mesoporous s ol gel titania film was developed for preconcentration/separation of trace V, Cr, and Cu by CME. The sorbed analytes were eluted for electrothermal vaporization inductively coupled plasma mass spectrometry (EVT ICP MS) determination of the trace element io ns in environmental and biological samples [82]. In this work, the properties, stability, and other factors of the sol gel titania coating affecting the sorption behaviors of V, Cr, and Cu were investigated. Alumina, due to its high surface area, mechanic al strength, thermal and chemical stability, has been widely used in the area of sample purification [163] and analytical separations [164, 165]. The surface chemistry of alumina is quite different from that of silica. Silica has a weak Brnsted acidity du e to the silanol groups, while alumina provides well Lewis acidity and basicity as well as a low concentration of Brnsted acid

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70 sites [138]. Both Brnsted and Lewis acid base characteristics are responsible for the chromatography performance of alumina. Th e surface chemistry of alumina is more sililar to that of zirconia than to silica. Thus, it is reasonable to expect rather more complex surface properties. As compared to silica, alumina is capable of both ion and ligand exchange [166]. The ligand exchange ability of alumina originates from the presence of Lewis acid sites on the surface, i.e., coordinatively unsaturated Al 3+ and water molecules or other easily displaced ligands coordinatively bond to the sites [138, 166]. Lewis basic analytes containing p olar functional groups can substitute for the surface hydroxyl groups or coordinated water molecules and form complexes with the metal ions of the oxide surface [154, 167] and so ligand exchange interaction can play an important role for selective extracti on of these compounds by alumina based sorbents. Alumina based sol gel sorbents were prepared from a highly reactive precursor, alumina sec butoxide, and a sol gel active organic polymer (hydroxyl terminated polydimethylsiloxane) [167]. The resultant sol g el alumina OH TSO coating had superior ligand exchange ability, thus it extracted polar compounds such as fatty acids, phenols, alcohols, aldehydes, and amines. It also demonstrated outstanding pH usage range, good thermal stability, and good coating prepa ration reproducibility. When applied in analysis of volatile alcohols and fatty acids in beer, the alumina OH TSO coating provided recoveries ranging from 85.7% to 104% and the relative standard deviation values of less than 9% for all the analytes [167]

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71 2.11 Reference s for chapter two [1] C. J. Brinker, G. W. Scherer, Sol Gel Science: The Physics and Chemistry of Sol Gel processing, Academic Press, San Diego, CA, 1990 [2] A. T. Papacidero, L. A. Rocha, B. L. Caetano, E. Molina, H. C. Sacco, E. J. Nas sar, Y. Martinelli, C. Mello, S. Nakagaki, K. J. Ciuffi, Colloids Surf. A 275 (2006) 27. [3] T. Muromachi, T. Toshifumi, K. Kamitani, K. Maeda, J. Sol Gel Sci. Technol. 40 (2006) 267. [4] M. D. Taylor, A. K. Bhattacharya, J. Mater. Sci. 34 (1999) 1277. [5] Y. S. Lin, I. Kumakiri, B. N. Nair, H. Alsyouri, Sep. Purif. Methods 31 (2002) 229. [6] U. Schubert, New J. Chem. 18 (1994) 1049. [7] J. Blum, D. Avnir and H. Schumann, C hem. T ech. 29 (1999) 32 [8] O. S. Wolfbeis, R. Reisfeld I. Oehme, Struct. Bon d. 85 (1996) 51. [9] Lin and C.W. Brown, Trends Anal. Chem. 14 (1997) 200. [10] C. J. Brinker, N. K. Raman, M. N. Logan, R. Se hgal, R.A. Assink, D. W. Hua T. L. Ward, J. Sol gel Sci. Technol. 4 (1995) 117. [11] Z. Zeng, W. Qiu Z. Huang, Anal. Chem. 73 (2001) 2429. [12] R. Gvishi, U. Narang, G. Ruland, D. N. Kumar P. N. Prasad, Appl. Organomet. Chem. 11 (1997) 107. [13] D. Levy L. Esquivias, Adv. Mater. 7 (1995) 120. [14] D. Levy, Chem. Mater. 9 (1997) 2666. [15] B. Dunn, G. C. Farrington B. Katz Solid State Ionics 70 (1994) 3. [16] S. Skaarup, K. West, B. Zachau Christiansen, M. Popal, J. Ka ppel, J. Kron, G. Eichinger G. Semrau, Electrochim. Acta 43 (1998) 1589. [1 7 ] J. Blum, D. Avnir H. Schumann, Chem. Tech. 29 (1999) 32

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76 [9 9 ] K. R. Alhooshani, Sol gel Zirconia and Titania based Surface bonded Hybird Organic Inorganic Coatings for Sample Preconcentration and Analysis vi a Capillary Microextraction In Hyphenation with Gas Chromatogrphy (CME GC). Ph.D. dissertation, Department of Chemistry, University of South Florida, Tampa, FL 2005. [ 100 ] R. Maleki, K. Farhadi A. A. Matin, Anal. Sci. 22 ( 2006) 1253 [ 101 ] A. A. Matin, R. Maleki, M. A. Farajzad eh, K. Farhadi, R. Hosseinzadeh A. Jouyban, Chromatographia 66 (2007) 383 [ 102 ] K. Farhadi, M. Mamaghanian, R. Maleki, J. Hazard. Mater. 152 (2008) 677. [ 103 ] D. Budziak, E. Martendal, E. Carasek, Anal Chim Acta 629 (2008) 92 [10 4 ] H. Bagheri, A. Es haghi, M. Rouini, J. Chromatogr. B 818 (2005) 147. [10 5 ] Z. Wang, C. Xiao, C. Wu, H. Han, J. Chromatogr. A 893 (2000) 157. [10 6 ] A. F. P. Biajoli, F. Augusto, Anal Sci 24 (2008) 1141 [10 7 ] F. Zheng, B. Hu, Spectrochim. Act a, Part B 63 (2008 ) 9 [10 8 ] H. Bagheri, A. Aghakhani, A. Es Haghi, C hromatographia 66 (2007) 779 [10 9 ] J. Cai, J. Xing, L. Dong, C. Wu, J. Chromatogr. A 1015 (2003) 11. [1 10 ] J B Zeng, J M. Chen, Z Q. Lin, W F. Chen, X. Chen, X R.Wang, Anal Chim Ac ta 619 (200 8) 59 [1 11 ] S. S. Segro, A. Malik, J. Chromatogr. A 1205 (2008) 26 [1 12 ] X R. Xia, R.E. Baynes, N.A. Monteiro Riviere, J.E. Riviere, Anal. Chem. 76 (2004) 4245 [11 3 ] Y L. Wang, Z R. Zeng, M M. Liu, M. Yang, C Z. Dong, Eur. Food Res. Tech nol. 226 (2008) 1091. [11 4 ] X. Li, Z R. Zeng, Y. Xu, Anal. Bioanal. Chem. 386 (2006) 1428. [11 5 ] X. Zhou, X. Li, Z Z Zeng, J. Chromatogr. A 1104 (2006) 359. [11 6 ] L F. Zhang, X J. Li, C X. Liu, Z R. Zeng, Fenxi Huaxue 35 (2007 ) 1269 [117] C Z. Dong, Z R. Zeng, X J. Li, Talanta 66 (2005) 721

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77 [11 8 ] X W. Zhou, X J. Li, Z R. Zeng, Sepu 24 (2006) 1. [11 9 ] J. Zhou, Z R Zeng, Anal Chim Acta 556 (2006) 400. [1 20 ] Y. Fu, Y. Hu, Y. Zheng, G. Li, J. Sep. Sci. 29 (2006) 2684. [1 21 ] Y. Feng, M. Xie, S. Da, Anal. Chim. Acta 403 (2000) 187. [1 22 ] J. Zhou, F. Yang, D. Cha, Z. Zeng, Y. Xu, Talanta 73 (2007) 870 [12 3 ] X. Li, Z. Zeng, Y. Xu, Anal. Bioanal.Chem. 384 (2006 ) 1428 [12 4 ] W N. Guan, F. Xu, M. Lian, Y. Xu, Y F. Guan, Sepu 25 (2007) 614 [12 5 ] M. Matos de Souza, J. H. Bortoluzzi, E. Carasek, Microchi m. Acta 155 (2006) 465 [12 6 ] M M. Liu, Z R. Zeng, H F. Fang, J. Chromatogr. A 1076 (2005) 16. [12 7 ] D M. Cha M M. Liu Z R. Zeng C. Dong G Q. Zhan Anal Chim Acta 572 (2006 ) 47 [12 8 ] H F. F ang, M M. Liu, Z R. Zeng, Talanta 68 (2006) 979 [12 9 ] Y. L. Hu, Y L. Fu, G K. Li, Anal Chim Acta 567 (2006) 21 1. [1 30 ] Z. Zeng, W. Qiu, M. Yang, X. Wei, Z. Huang, F. Li, J. Chromatogr. A 934 (2001) 51. [1 31 ] J X. Yu, C Y. Wu J. Xing, J. Chromatogr A 1036 (2004) 101 [1 32 ] L S. Cai, S L. Gong, M. Chen, C Y. Wu, Anal Chim Acta 559 (2006) 89 [13 3 ] M M. Liu, Z R. Zeng, Y. Lei, H B Li, J. Sep. Sci. 28 (2005 ) 2306. [13 4 ] C Z. Dong, Z R. Zeng, M. Yang, Water Res 39 (2005) 4204. [13 5 ] S. S. Segro A. Malik J. Chromatogr. A 1200 (2008) 62. [13 6 ] G. Antonia de Silva, F. Augusto, R. Poppi, J. Chromatogr. A 1138 (2007) 251 [1 37 ] A. Wehrli, J. C. Hildenbrand, H. P. Keller, R. Stampfli, R. W. Frei, J. Chromatogr. 149 ( 1978 ) 199

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78 [ 138 ] J. Nawrocki, C. Dunlap, A. McCormick, P. W. Carr, J. Chromatogr. A 1028 ( 2004 ) 1 [ 139 ] J. L. Glajch, J. J. Kirkland, J. Koehler, J. Chromatogr. 384 ( 1987 ) 81 [ 1 4 0 ] D. V. McCalley, J. Chromatogr. A 902 ( 2000 ) 311 [ 141 ] L. R. Synder, J. K. Glajch, J. J. Kirkland, Practical HPLC Method Development Wiley Interscience, New York, 1996. [ 142 ] Neus, U. D. Encyclopedia of Analytical Chemistry, Wiley, NY, 2001. [ 143 ] J. J. Kirkland, J. L. Glajch, R. D. Farlee, Anal. Chem. 61 ( 1989 ) 2 [ 144 ] L. C. Sander, S. A. Wise, Cri t. Rev. Anal. Chem. 18( 1987 ) 299 [ 145 ] T. Y. Kim, Novel Sol gel Titania based Hybird Organic Inorganic Coatings for On Line Capillary Microextraction Coupled to High Performance Liquid Chromatography. Ph.D. dissertation, Department of Chemistry, Universi ty of South Florida, Tampa, FL 2006. [ 146 ] M. Kawahara, H. Nakamura, T. Nakajima, J. Chromatogr. 515 (1990) 149 [ 147 ] B.C. Trammell, M.A. Hillmyer, P.W.Carr, Anal. Chem. 73 (2001) 3323 [1 48 ] L. Sun, M. J. Annen, F. Lorenzano Porras, P. W. Carr, A.V. M cCormick, J. Colloid Interface Sci. 163 (1994) 464 [14 9 ] J. Yu, Z. E l Rassi, J. Chromatogr. A 631 (1993) 91 [15 0 ] J. Nawrocki, C. J. Dunlap, P.W. Carr, J. A Blackwell, Biotechnol. Prog. 10 (1994) 561 [1 51 ] C. J. Dunlap, C.V. McNeff, D. Stoll, P. W. C arr, Anal. Chem. 73 (2001) 598 A [1 52 ] M. Xie, Y. Feng, S. Da, J. Sep. Sci. 24 (2001) 62 [1 53 ] M. Xie, Y. Feng, S. Da, D. Meng, L. Ren, Anal. Chem. Acta 428 (2001) 255 [ 154 ] J. Winkler S. Marme, J. Chromatogr. A 888 (2000) 51 [ 155 ] Z. T. Jiang Y. M. Zuo, Anal. Chem. 73 (2001) 686 [ 156 ] K. Tani Y. Suzuki, J. Chromatogr. A 722 (1996) 129

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79 [ 157 ] C. Fujimoto, Electrophoresis 23 (2002) 2929 [ 158 ] P. Tsai, C T. Wu C.S. Lee J. Chromatogr. B 657 (1994) 285 [ 159 ] A. Ellwanger, M. T. Matyska, K. Alb ert J. J. Pesek, Chromatographia 49 (1999) 424 [ 160 ] A.Y. Fadeev and T.J. McCarthy J. Am. Chem. Soc. 121 (1999) 12184 [ 161 ] K.V. P. M. Shafi, A. Ulman, X. Yan, N L. Yang, M. Himmelhaus M. Grunze, Langmuir 17 (2001) 1726 [162] X J Li, J. Gao, Z R Zeng Anal Chim Act a 590 (2007) 16 [ 163 ] B. Kasprzyk Hordern, Adv. Colloid Interface Sci. 110 (2004) 19. [ 164 ] M. M. Acanski, J. Serb. Chem. Soc. 68 (2003) 163 [165] J. J. Pesek M. T. Matyska, J. Chromatogr. A 952 (2 002) 1 [166] H. A. Claessens M. A. Van Straten, J. Chromatogr. A 1060 (2004) 23 [167] M M Liu, Y. Liu, Z R Zeng, T Y Peng J. Chr omatogr. A, 1108 (2006) 149

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80 CHAPTER THREE GERMANIA BASED SOL GEL HYB RI D ORGANIC INORGANIC COATINGS FOR CAPILLARY MICROEXTRA CTION AND GAS CHROMATOGR A PHY 3. 1 Introduction of germanosilicate glasses material In recent years silica glasses containing germanium dioxide (germanosilicate glasses) have attracted considerable interests due to their various appealing properties. Most o f them are related to the composition and to the structure of the glass [1] As an isostructural analogue of SiO 2, GeO 2 is well compatible with the silica network; it is employed as a refractive index modifier in binary xSiO 2 (1 x) GeO 2 glasses for optics The presence of Ge atoms modifies the atomic structure and causes both permanent and photo induced variation of the refractive index [ 2 3]. Ge doped silica glasses have attracted much attention for giving rise to phenomena such as photosensitive grating effects and second harmonic generation (SHG) [ 4, 5]. The low phonon energy of germania is also another interesting property because it can be used to produce low losses optical waveguides and amplifiers [6]. For their intrinsic characteristics such as insu lating behavior, low phonon energy with respect to the silicate glasses, transparency and homogeneity, SiO 2 GeO 2 glasses are good candidates as host matrixes for metal or semiconductor clusters for optical applications. Significant attention has been furth er devoted to these remarkable optical properties of these binary systems manifested in different optical and opto electronic phenomena.

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81 The photosensitivity exhibited by these materials is ascribable to the presence of germanium dioxide and to the occurre nce of germania related defect center. From a structural point of view, each Ge atom could be substitutional to a Si atom and could be bonded to four O atoms, or it could be under coordinated giving rise to oxygen deficient centers (GODC) [ 7]. It is well k nown that there is an UV absorption band near 5 eV for germanosilicate material and that this absorption is associated with an oxygen deficient defect [ 8, 9]. A 5 eV absorption band of germania related oxygen deficient defects is responsible for the photos ensitivity of germanium oxide based materials [ 1 0 1 1]. Both silica and germania are prototypes of simple glasses consisting of corner shared TO 4 (T = Si, Ge) tetrahedra linked in a random network structure. T O T bond angles are estimated by X ray diffra ction to be 144 in SiO 2 glass and 133 in GeO 2 glass. Besides the structural similarities, a striking difference between these two systems is the concentration of defects. In pure silica, they are of order of 10 9 of the total Si atoms [ 1 2], while in p ure germania or in binary SiO 2 GeO 2 glasses the concentration is around 10 3 10 4 of the total germanium sites. This difference has been ascribed to different lead of thermodynamic stability for SiO 2 and GeO 2 From a thermodynamic point of view, at ro om temperature, formation of SiO 2 quartz is favored with respect to GeO 2 in the hexagonal form. Moreover, the latter is much less stable than SiO 2 GeO 2 may occur in either the 4 quartz structure, or the 6 fold coordination of th e rutile structure. However, although both GeO 2 polymorphs exist at quartz structure is metastable [ 1 3].

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82 3. 2 Preparation of s ol gel GeO 2 /ormosil organic inorganic hybrid material Various methods including melting, flame hydrolysis, vapour axial deposition (VAD), sputtering deposition, chemical vapour deposition (CVD), ion implantation and sol gel technology have been employed to fabricated GeO 2 based materials [ 1 4]. Among the synthetic methods, t he sol gel route has gained great interest during recent years for making advanced materials and in particular for preparation oxide based coatings and it has gained great interest in preparing Ge doped SiO 2 glasses. Germanium alkoxide typically undergo po lymerization via hydrolysis and condensation reactions similar to those seen in the case of alkoxysilanes (Scheme 3. 1). When GeO 2 is mixed with vitreous silica at a molecular level, Ge atoms would randomly substitute Si atoms in SiO 4 tetrahedra so that the microstructure of the glass would remain a continuous three dimensional network consisting of interconnected SiO 4 and GeO 4 tetrahedea [ 1 5]. Scheme 3.1 Typical hydrolytic ploycondensation of g ermanium alkoxide to form g ermania [ 1 6]

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83 Sol gel method is a solution based chemical process from which inorganic organic hybrid materials can be synthesized through hydrolysis and condenstation reactions. The components involved are well mixed at the molecular level, providing good cont rol of chemical compositions film homogeneity. Interests in using the sol gel method to fabricate germanosilicate coatings originate from the advantages that it offers: homogeneity, ease of composition control, ability to fabricate large area coatings, and low equipment coat. Materials for photonics require a very high level of purity and homogeneity. Sol gel processing is therefore an important route to fabricating GeO 2 based materials with high degree of purity, and homogeneity as well as advanced and con trolled properties [7]. Compared with the conventional glasses and glass ceramic processes the sol gel technique has the notable advantages of provid ing chemical homogeneity at relatively low process temperatures. In the case of multicomponent systems it provides a more uniform phase distribution and the possibility of preparing new crystalline and non crystalline materials [ 1 4]. In addition, because sol gel based glass can be prepared on the basis of chemical reactions involving a solution, this process i s very suitable to fabricate glassy and crystalline films or coatings. It has been widely used to produce various kinds of functional films, coatings, hollow core fibers, concavo convex cavity waveguides, etc. and organic or inorganic materials [ 1 4]. 3. 3 Ormosil precursors at low treatment temperature Sol gel germanosilicate synthesis usually starts from solutions of silicon and germanium alkoxides at a low germania content. In reported GeO 2 based material system,

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84 tetraethylorthosilicate (TEOS) is general ly employed as a SiO 2 source, and TEOG is generally used as GeO 2 source. However, the heat treatment temperature for TEOS is quite high (around 1000 C). Therefore, it is difficult to produce a film thicker than 0.2 coating process in a single purely inorganic sol gel layer [ 1 7]. This is because high curing and sintering temperatures necessary for densification of the final materials causes a large shrinkage of the film during the thermal densification process which leads to the cracking in a thicker layer and then leads to possible stress fracture [ 1 8, 1 9]. The use of organically modified alkoxysilane precursors helps overcome this problem. Since silica precursors can produce a relatively thick single coating layer at a low temperature or even room temperature [ 2 0 1 2] without cracking. Methyltrimethoxysilane (MTES) has been used as precursors for the hybrid material to provide SiO 2 source [ 2 3] A GeO 2 /Methyltrimethoxysilane sol gel processed hybrid thin film has been fabricated by acid catalyzed solutions of methyltrimethoxysilane (MTES) mixed with germanium isopropoxide. A single layer coating with a thickness of about 1.3 tained on silica on silicon substrate by single spin coating process at a heat treatment temperature of 100 C. The result indicated that a heat treatment temperature below 300 C is expected to produce a dense, low absorption, high transparent hybrid wave guide film for photonic applications. The introduction of MTES provides the advantage of producing thicker and denser films at low temperature. glycidoxypropyltrimethoxysilane orgnic inorganic hybrid has also been prepared by a sol gel technique and a spin coating process. The result indicated that a heat treatment temperature below 300 C is expected to produce a dense, low absorption,

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85 highly transparent hybrid film. The introduction of ormosinl GLYMO, provides the advantage of producing thick a nd dense films at low temperature [ 2 4 2 8]. Ormosil based organic inorganic hybrid materials have been studied as a promising system for photonic applications in recent years. This is because organic groups are integrated in the glass and the bulky organic components fill the pores between the inorganic oxide chains. 3. 4 Problems of germanosilicate material during sol gel process There are disadvantages to fabricate germanosilicate using sol gel process. It is well known that cracks and crystallization co uld be easily occor in the sol gel materials. Since germanium ethoxide hydrolyzes extremely fast and the resulting sol gel materials are likely to crack, the production of thick, crack free GeO 2 SiO 2 sol gel films with high GeO 2 content is very difficult. It has been reported by Kozuka et al that the maximum thickness achievable without crack formation via non repetitive deposition is often below silicate oxide films [ 2 9]. It was also reported that although germanosilicate films containing u p to 45 mol % germanium oxide were fabricated, the 3 0]. Thus, cycles of dip coating are widely used to deposit thick sol gel films to overcome this problem. However, generally the lifetime of GeO 2 SiO 2 sol with a high TEOG content is too short to perform cycles of dip coating. Therefore, a coating sol solution with a long gelation time is needed. To reach this goal, techniques capable of suppressing the increase in sol viscosity and the crack formation in sol gel f ilms with a high GeO 2 content are in great demand. Jing et al

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86 developed a new sol gel route to fabricate germansilicate film by using diethylorthosilicate (DEOS) and TEOG as the precursors for SiO 2 and GeO 2 [30]. A thick free SiO 2 GeO 2 film containing up to 70 mol % germanium oxide were obtained. By comparing TEOS and DEOS, they pointed out different precursors differed greatly during ageing although they had the same molar ratio of SiO 2 to GeO 2 The sol synthesized using TEOS and TEOG as raw material exhibited very poor stability and the use of DEOS as precursor for silica is of great help in stabilizing the sol by maintaining low viscosity for 280 h. In the work, they also explained the reason from t he structural point of view of the colloidal particles. On the other hand, sol gel processing of oxide materials, bulk and thin films, requires a high firing temperature to achieve a full densification. During this process some oxides show a tendency to cr ystallize. This is actually the case of several oxides such as titania [ 3 1]. The crystallization of germania generally took place at temperatures higher than 500 C, and a full densification cannot be achieved without avoiding a partial crystallization of the system. Therefore it is a difficult problem to solve when sol gel processing is employed for fabrication process. The limitation in a wider application of the hybrid materials is the lack of a deeper knowledge and control of their structure. It was obs erved that control of the hybrid structure through an appropriate and reproducible synthesis is a difficult task. 3. 5 Introduction of g ermania based sol gel organic inorganic hybrid coatings for capillary microextraction and gas chromatography Solid phase microextraction (SPME) [ 32 ] is an effective approach to solvent free sampling and sample preparation for laboratory and field analyses. Developed in 1989 by

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87 Belardi and Pawliszyn [ 33 ] SPME integrates sampling, sample preparation, and analyte preconc entration into a single step procedure characterized by ease and simplicity. By eliminating the use of organic solvents, SPME overcomes the limitations inherent in conventional sample preparation techniques like liquid liquid extraction (LLE), Soxhlet extr action, solid phase extraction (SPE), etc. As a simple, sensitive, time effective, easy to automate, and portable sample preparation technique, SPME has been successfully applied to a variety of analytes in environmental [ 43 36 ], biological [ 37 39 ], food [ 40 ], drug [ 41 43 ], flavor [ 44 ] and other types of samples in hyphenation with gas chromatography (GC) [ 45 ], high performance liquid chromatography (HPLC) [ 46 ], capillary electrophoresis (CE) [ 47 ], and Mass spectrometry (MS) [ 48 ]. In spite of its popularit y and wide acceptance, fiber SPME (the dominant format of SPME) possesses a number of inherent deficiencies arising from the fiber design and its syringe based mechanical operation. In fiber SPME, the protective polyimide coating is removed from the extern al surface of a fused silica fiber end segment (~ 1 cm). A sorbent layer created and on this end segment, serves as the SPME extracting phase. The lack of external protective coating makes the end segment as well as the sorbent phase coated on it vulnerabl e to mechanical damage during operation and handling of the SPME device. The short length (~ 1 cm) of the coated segment results in low sorbent loading, which leads to reduced extraction sensitivity. Moreover, fiber SPME is difficult to couple to high perf ormance liquid chromatography (HPLC) and other liquid phase separation techniques. A number of SPME variants [ 49 53 ] have been proposed to overcome these difficulties. Among them, in tube SPME [ 54 56 ] holds great promise,

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88 especially for effective hyphenati on with liquid phase separation techniques. In tube SPME (also termed capillary microextraction (CME)) [ 57 ], is practically free form the shortcomings inherent in conventional fiber SPME. Unlike fiber SPME, where a sorbent coating on the outer surface of a small diameter solid rod serves as the extraction medium, CME typically uses a piece of fused silica capillary with a stationary phase coating on its inner surface (e.g., a short piece of GC column) to perform extraction. In CME, the protective polyimide coating on the external surface of the capillary remains intact and provides reliable protection against mechanical damage to the capillary. Moreover, in tube SPME provides a simple, easy, and convenient way to couple SPME to gas as well as to liquid pha se separation techniques. Despite all these advantageous features, in tube SPME still suffers from other shortcomings that originate from the stationary phase coating on the inner surface of a short piece of conventionally coated GC capillary column typica lly used as in in tube SPME device. First, the low stationary phase loading which leads to low sample capacity and reduced extraction sensitivity of the technique. Increasing the coating thickness is a possible way to solve this proble m [ 58 59 ]. However, it is extremely difficult to reliably immobilize thicker coatings using conventional approaches [ 60 ]. Second, conventionally prepared GC coatings are not chemically bonded to the fused silica capillary inner surface. This lack of chemi cal bonds is mainly responsible for the low thermal and solvent stability of conventionally prepared coatings [ 61 ]. When used in hyphenation with GC, low thermal stability of the SPME coatings forces one to use low desorption temperatures to preserve

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89 coati ng integrity, which in turn, results in incomplete sample desorption and sample carry over problems. Low solvent stability of the sorbent coating, on the other hand, prevents effective hyphenation of in tube SPME with liquid phase separation techniques tha t employ organic or organo aqueous mobile phases [ 62 ]. Obviously, sorbent coating stability plays a fundamentally important role in solid phase microextraction both fiber based and capillary based. Further advancements in these areas will greatly depend on improvements and new breakthroughs in sorbent development and coating technology. In recent years, sol gel technology has attracted considerable interest among analytical chemists. Sol gel chemistry provides an effective pathway for the synthesis of adv anced organic inorganic hybrid materials [ 63 ] in a wide variety of forms. The mild thermal conditions typical of sol gel reactions not only allow chemical incorporation of a wide range of chemical species in the created material systems but also ease the r equirements for laboratory operation and safety. Sol gel technology allows the use of a wide range of chemicals (both organic and inorganic) to integrate desirable properties in a single material system. Thanks to all these advantages, sol gel chemistry is receiving increased attention as an effective tool for the synthesis of advanced stationary phases and extraction media for modern analytical techniques. In recent years, sol gel chemistry has been the used to prepare highly stable surface bonded coatings or monolithic beds within capillaries for use as chromatographic stationary phases and sorbents for microextraction techniques [ 57 63 64 70 ] Silica based stationary phases and sorbents are predominantly used in modern separation and sample preparation techniques. Silica surface chemistry and surface

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90 modification process are well understood. However, the limitations of siliceous materials are also well known. The pH stability problem is a major drawback of silica based stationary phases and extraction me dia. Siloxane bond (Si O Si) on the silica surface hydrolyzes at pH > 8 [ 71 ] and it happens rapidly under elevated temperatures [ 72 ]. Under acidic conditions, siloxane bond is also unstable [ 73 ], and it gets worse with elevated temperatures [ 74 ]. Transiti onal metal oxides such as zirconia, titania, and alumina are interesting materials to offer better chemical and thermal stabilities [ 72 ], and have attracted attention of separation scientists. Although titania alumina and zirconia based sol gel systems [75 77 ] that demonstrated high chemical and pH stabilities in applications, surface modification of these systems is rather hard. The precursor selections for transitional metal systems are limited. Therefore, we are interested in investigating novel non s ilica sol gel system and their application in separation material. Germania as an isostructural analog of silica, can be expected to offer advanced material properties for analytical separation and sample preparation. However, the potentials and promises o f these novel materials in analytical chemistry remained practically unexplored. In this work, for the first time, the preparation of germania based hybrid organic inorganic sol gel coatings for capillary microextraction was explored. The great performance of sol gel germania based coatings in CME, and the preliminary GC results that point to the analytical potential of such coatings as GC stationary phases was presented.

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91 3 6 Experimental 3 6 .1 Equipment Capillary microextraction gas chromatography (CME GC) experiments with sol gel germania coated capillaries were carried out on a Shimadzu Model 14A GC system equipped with a flame ionization detector (FID) and a split/splitless injector. An in lab designed liquid sample dispenser [ 57 ] was used to perform capillary microextraction via gravity flow of aqueous samples through the sol gel microextraction capillary. A Fisher Model G 560 Genie 2 vortex (Fisher Scientific, Pittsburgh, PA) was used for thorough mixing of sol solution ingredients. A Micromax model 3590F microcentrifuge (Thermo IEC, Needham Heights, MA) was used for centrifugation at 14,000 rpm (15,682 x g) to separate out the precipitate from the sol solution. A home built gas pressure operated filling/purging device [ 78 ] was used to perform a numb er of operations: (a) filling the extraction capillary with the sol solution, (b) expelling the solution from the capillary after predetermined period of in capillary residence, (c) rinsing the capillary with a suitable solvent to clean the coated surface, and obtained from a Barnstead Model 04741 Nanopure deionized water system (Barnstead/Thermodyne, Dubuque, IA). Online data collection and processing were accomplished us ing ChromPerfect (version 3.0) computer software (Justice Laboratory Software, Denville, NJ).

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92 3 6 .2 Chemicals and materials Fused was purchased from Polymicro Technologies Inc. ( Phoenix, AZ). HPLC grade solvents (methylene chloride, methanol, and tetrahydrofuran (THF)) were purchased from Fisher Scientific (Pittsburgh, PA). Fluorene, phenanthrene, naphthalene, pyrene, chrysene, butyrophenone, heptanophenone, hexanophenone, decanop henone, trans chalcone, nonanal, decanal, undecanal, dodecanal, tridecanal and trifluoroacetic acid (TFA, 99%) were purchased from Acros Organics (Pittsburgh, PA). Hydroxy terminated polydimethylsiloxane (PDMS) and hydroxy terminated polydimethyldiphenylsi loxane (PDMDPS) were purchased from United Chemical Technologies Inc. (Bristol, PA). Tetramethoxygermane (TMOG) and 3 aminopropyltrimethoxysilane (APTMS) were obtained from Gelest, Inc (Morrisville, PA). 3 6 .3 Preparation of sol gel germania PDMS coated ca pillaries for CME The coating sol solution was prepared in a clean polypropylene centrifuge tube using 100 mg of hydroxy terminated PDMS, 20 followed by centrifugation for 5 min to remove possible precipitates. The clean supernatant was transferred to another clean vial, disc arding the precipitate. A hydrothermally pretreated [ 79 ] fused silica capillary (1 m) was filled with the clear sol solution using pressurized helium (50 psi) in a filling/purging device. The sol solution was allowed to stay inside the capillary for 15 min to facilitate the formation of a sol gel coating. During this in capillary residence period, a 3 dimensional sol gel network was

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93 formed in the sol solution due to hydrolytic polycondensation reactions. In this process, patches of the sol gel network evolv ing in the vicinity of the capillary inner surface had the favorable conditions to get chemically bonded to the capillary walls due to condensation reactions between the sol gel active groups on the sol gel network fragments and the silanol groups on the c apillary surface. Following this, the unbonded portion of the sol solution in the central part of the capillary was expelled under helium pressure (50 psi) and the coated surface was purged with helium (50 psi) for an hour, leaving behind a dry surface bon ded sol gel coating on the capillary inner walls. The capillary was further conditioned under helium purge by programming the temperature from 40 C to 300 C at 1 C/min and held at the final temperature for 5 hours. The sol gel coated microextraction cap illary was then rinsed with a 1:1 (v/v) mixture of methylene chloride and methanol (2 mL), and then the capillary was conditioned again from 40 C 300 C at 5 C/min. The conditioned capillary was then cut into 10 cm long pieces that were ready for use i n capillary microextraction. Sol gel germania PDMDPS and sol gel germania APTMS coated capillaries were prepared in an analogous way by replacing hydroxyl terminated PDMS in the sol solution either by hydroxyl terminated PDMDPS or APTMS. A sol gel germania PDMS coated GC column was prepared following a similar procedure carried out within a 5 m piece of hydrothermally treated fused silica capillary using a more dilute coating sol solution containing PDMS (200 mg), TEOG 2 O), and CH 2 Cl 2

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94 3 6 .4 Preparation of silica based sol gel PDMS columns for GC analysis The extracted analytes were separated by GC using a silica based sol gel capillary column that was also prepared in hous e following a modified version of the original procedure described by us elsewhere [ 63 ]. chloride and TFA (with 5% of water) [ 63 ], ter) to prepare the sol solutions used in coating the GC columns. 3 6 .5 Preparation of aqueous samples for CME GC Sample solutions were prepared in several stages. Solute chemical standards were first dissolved in methanol or THF to obtain the stock solut ions (10 mg/mL), which was further diluted to 0.1 mg/mL in the same solvent. The final aqueous solution was prepared by additionally diluting this solution in water to achieve ng/mL level concentrations. The aqueous solutions were freshly prepared prior to performing the microextraction experiments. The used glassware was properly deactivated to avoid analyte loss due to adsorption on the glassware surface [ 57 ] 3 6 .6 Gravity fed sample dispenser for capillary microextraction An in lab designed gravity fed sample dispenser [ 57 ] was used for capillary microextraction. It offered a consistent means to extract analytes by passing the liquid sample through the microextraction capillary under gravity, as well as a convenient way to clean the capillary via rising and purging. It was built by modifying a Chromaflex AQ column (Kontes Glass Co., Vineland, NJ) consisting of a thick walled Pyrex glass cylinder concentrically placed in an acrylic jacket. The inner surface of the glass cylinder

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95 was deactivated by treating with HMDS solution as described previously [ 57 ]. 3 6 .7 Sol gel capillary microextraction. A 10 cm long segment of previously conditioned hybrid sol gel germania coated empty sample dispenser. A 50 mL volume of the aqueous sample solution was then poured into t he dispenser from the top. The sample solution was allowed to pass through the microextraction capillary under gravity. During this process, the analyte molecules were extracted by the sol gel germania hybrid coating residing on the inner walls of the capi llary. With the progression of this microextraction process, concentration equilibrium was established between the sol gel sorbent coating and the sample solution (typically within 30 40 min). The capillary was then removed from the sample dispenser, brief ly purged with helium, and connected to the inlet end of the GC column using a two way press fit connector. The free end of the microextraction capillary was introduced into the GC injection port (from the bottom end of the port previously cooled down to 3 0 C) so that ~8 cm of the capillary resided inside the quartz liner in the injection port. A graphite ferrule was used to secure a leak free connection between the capillary and the lower end of injection port. The extracted analytes were then thermally desorbed from the capillary in the splitless injection mode by rapidly raising the temperature of the injector (from 30C to 300C in five min) and the desorbed analytes were transported to the GC column by the helium flow through the injector. The desorbe d analytes were focused at the inlet of the GC column held at 30 C. Analyte desorption and focusing was performed over a 5 min period. The GC column temperature was then raised @ 20 C/min to

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96 facilitate transportation of the focused solutes through the co lumn providing their GC separation. A flame ionization detector (FID), maintained at 350 C, was used for analyte detection. 3 6 .8 Safety precautions The presented work involved the use of various chemicals (organic and inorganic) that may be environmental ly hazardous with adverse health effects. In accordance with material safety data sheet (MSDS) proper safety measures were taken in handling strong acids, bases and organic solvents such as methanol, methylene chloride, and acetonitrile. All used chemicals were disposed in the proper waste container to ensure personnel and environmental safety. 3 7 Results and discussion 3 7 .1 Chemical reactions involved in the preparation of sol gel germania coatings Sol gel chemistry provides a powerful tool for the des ign and synthesis of novel materials in desirable formats including thin films, monolithic beds, spherical particles, etc. It provides the ease and flexibility in synthesis thanks to mild reaction conditions. In general, a sol gel process involves chemica l reactions that convert simple sol gel active precursor molecules into an intermediate colloid state called the sol and then into a three dimensional polymeric network structure (with solvent filled pores) called the gel. The sol gel active components in the sol solution include one or more sol gel precursors (typically alkoxides), various hydrolyzed forms of the precursors and certain hydroxy or alkoxy terminated polymers. Two key chemical reactions take place in the sol gel process:

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97 (a) hydrolysis of th e sol gel precursor, and (b) polycondensation of the hydrolyzed precursors among themselves and/or with other sol gel active components of the sol solution. Besides silica based precursors, metal alkoxide based sol gel precursors are often used together wi th other sol gel active components in the coating solution to create a wide variety of material systems with desired properties. Zirconia titania and alumina based sol gel materials have already been prepared, and their various appealing properties (e. g., excellent pH stability) attracted considerable interest [ 72 ]. Since GeO 2 is well established as an isostructural analog of SiO 2 [ 80 ] and is compatible with the silica network, it presents great potential in materials synthesis. In this work, our aim wa s to use germanium alkoxide precursors in sol gel reactions to create germania based surface bonded organic inorganic hybrid coatings within fused silica capillaries and evaluate their performances as CME sorbents and GC stationary phases. Table 3. 1 lists the chemical ingredients used in the sol solution to in situ create germania based sol gel hybrid organic inorganic coatings within fused silica capillaries for use either in solvent free microextraction or in GC separations.

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98 Table 3.1 Chemical ingredients of the coating solution used in preparing sol-gel germania organic-inorganic hybrid coatings. Chemical Name Function Structure Tetramethoxygermane (TMOG) Hydroxy terminated polydimethylsiloxane (PDMS) Hydroxy terminated polydimethyldiphenylsiloxane (PDMDPS) 3 Aminopropyltrimethoxysilane (APTMS) Methylene chloride Trifluoroacetic acid (99%) Water Sol gel precursor Sol gel active polymer Sol gel active polymer Sol gel active polymer Solvent Catalyst Hydrolysis reagent CH 2 Cl 2 H 2 O

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99 Here, tetramethoxygermane served as the sol gel pre cursor and generated the inorganic component of the resulting hybrid sol gel organic inorganic coating. The hydroxy terminated PDMS or PDMDPS served as the source of the organic component of the hybrid coating, while APTMS played a dual role: it served as a sol gel precursor and also as the source of the organic (aminopropyl) ligand. An appropriate choice from these sol gel active organic ligands was made for use in the sol solution to create a sol gel germania coating with the desired organic ligand. For e xample, hydroxy terminated PDMS was incorporated in the sol solution to create a sol gel ( 3. 2 3. 3) to denote the residuals of these ligands incorporated into the sol gel stru cture. The following illustrates the creation of sol gel hybrid germania coatings using sol gel GeO 2 PDMS as an example, and involves the following chemical processes: (1) hydrolysis of the alkoxide precursor (TMOG) ( S cheme 3. 2 ), (2) polycondensation of the partially and/or fully hydrolyzed precursor molecules among themselves and with other sol gel active components of the solution ( S cheme 3. 3 ), (3) chemical bonding of PDMS to the evolving sol gel germania network, and (4) chemical anchoring of the evolv ing hybrid organic inorganic polymer to the inner walls of the capillary ( S cheme 3. 4 ). Scheme 3. 2 Hydrolysis of germania precursor (TMOG)

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100 Scheme 3. 3 Polycondensat ion of the hydrolyzed precursor and chemical bonding of the sol gel active organic ligand (Y) to the evolving sol gel network

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101 Scheme 3. 4 Chemical anchoring of the evolving sol gel germania hybrid organic inorganic polymer to the inner walls of a fused silica capillary

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102 The hydrolysis (partial or complete) of TMOG produces a variety of reactive hydroxyl containing species capable of undergoing condensation reactions with neighboring sol gel active chemical species in the sol solution including TMOG, APT MS and its hydrolyzed forms, hydroxy terminated polymers (PDMS and PDMDPS). Condensation of these reactive species leads to a hybrid organic inorganic material via chemical integration of an inorganic component (germania, originating from TMOG) and an orga ligands). The silanol groups residing on the inner walls of the fused silica capillary are also sol gel active, and can take part in the condensation reactions resulting in c hemical anchoring of the portion of the sol gel material evolving in the vicinity of the capillary walls. This surface bonded portion of the sol gel material is left on the column surface in the form of an organic inorganic hybrid coating and serves as the sorbent for solvent free microextraction. Sol gel process is complex and proper control of the processing parameters (e.g., drying temperature, pressure, pH, precursor/water molar ratio, solvent, and the structure of alkoxy groups, among others) is neces sary during various stages of the process (polymerization, gelation, drying) to prepare sol gel materials with desired structural characteristics [ 81 82 ]. In this work, experimental conditions were carefully optimized to obtain the germania based hybrid g el within 2 hours. This was accomplished through variation of relative proportions of various components of the solution. After coating and thermal conditioning, the capillary was rinsed with a mixture of methylene chloride and methanol to get rid of unrea cted chemical species physically adhering to the coating.

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103 3 7 .2 IR Characterization Figure 3. 1 represents two FTIR spectra for: (A) pure PDMS, (B) sol gel Germania PDMS Coating. According to literature data [ 83 ], Ge O Si vibration provides a characteristi c IR stretch at around 1000 cm 1 [ 84 ], which is determined by the vibrational modes associated with O in Ge O Si. Based on FTIR measurements in germania doped SiO 2 film sample, Mei et al [ 83 ] assigned the peak at 987 cm 1 to the Ge O Si vibration. However they also noted that a shift in the position of this characteristic peak is possible due to a difference in the proportions of Ge, Si, and O in the sample [ 85 ]. The FTIR spectrum for our sol gel germania PDMS (Figure 3. 1 B) coating contains a peak at 960 .43 cm 1 This peak is absent in the spectrum for pure PDMS (Figure 3. 1 A) and, and we attribute this to successful creation of sol gel germania PDMS hybrid material containing Ge O Si bonds. 3 8 CME profile for sol gel germania coated capillaries In capillary microextraction, it is desirable that the ex traction equilibrium is reached in the shortest possible time. In this work, we investigated the relationship between extraction time and the amount of analytes extracted in CME with sol gel germania PDMS coating (Figure 3. 2). As can be seen in F igure 3. 2 for both heptanophenone (a moderately polar solute) and pyrene (a nonpolar analytes), the extraction equilibrium was reached within 40 min. Based on this observation, 40 min extraction time was used in CME experiments presented in this paper.

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104 Figure 3. 1 A FTIR spectra representing: pure PDMS Figure 3. 1 B FTIR spectra represent ing: sol gel germania PDMS hybrid material used as a sorbent in capillary microextraction

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105 Figure 3. 2 Capillary microextraction profiles of pyrene and heptanophenone on a sol gel germania coated capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, gravity fed sample dispenser for extraction at room temperature. Ot her conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven temperature programmed from 30 C to 300 C at a rate of 20 C/m in; helium carrier gas; FID 350 C

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106 3 9 Extraction characteristics of sol gel germania coatings in CME By atomic structure, Ge and Si are closest neighbors located in Group 14 of the periodical table, and they have similar properties. GeO 2 is well kno wn as the isostructural analogue of SiO 2 which makes it compatible with the silica network. In this work, we prepared Germania based sol gel PDMS coatings and tested their performance in capillary microextraction coupled to GC FID. Our results suggest that sol gel Germania hybrid coatings have the ability to extract a wide range of analytes from aqueous media. Such sol gel coatings also provide outstanding solvent and pH stability which is difficult to achieve on pure silica based extraction material. 3 9 1 Extraction of non polar an d moderately polar compound s by s ol gel g ermania PDMS coated capillary for CME GC analysis The consistency in the performance of sol gel germania PDMS capillaries was characterized by the run to run and capillary to capillary RSD values for the extracted amounts in CME GC analysis. For this, aqueous samples of three different classes of analytes (PAHs, aldehydes, and ketones) were used. GC peak areas obtained from the extracted analytes were used as a measure of the extracted a mounts in CME. As we can see from T able 3. 2, the peak area run to run R.S.D values for PAH samples were below 6%, and those for GC retention time were less than 0.33 %. For aldehydes, the run to run peak area and GC retention time R.S.D values were under 6 .5 % and 0.2 % respectively. For ketones, the run to run peak area R.S.D value was under 7.2 % and that for retention time was within 0.23 The detection limit value for different classes of analytes is shown in Table 3.3.

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107 Table 3. 2 GC p eak area and reten tion time repeatability data for PAHs, aldehydes, and ketones extracted from aqueous samples by CME using a sol gel germania PDMS coated microextraction capillary Analyte Peak area repeatability (n= 3 ) t R Repeatability (n= 3 ) Class Name Mean pe ak area (aribitary unit) R.S.D. (%) Mean t R (min) R.S.D. (%) PAHs Aldehyde Ketones Naphthalene Fluorene Phenanthrene Pyrene Nonanal Decanal Undecanal Valerophenone Heptanophenone Hexanophenone Decanophenone 5.2 19.9 28.2 15.7 1.5 3.3 2.5 3.2 11.0 11.8 10.1 2.84 4.82 5.05 2.33 4.91 6.46 1.32 2.69 3.97 7.18 2.38 7.07 9.75 10.94 12.87 6.31 7.08 7.80 8.40 9.02 9.12 9.79 0.12 0.33 0.17 0.26 0.18 0.01 0.21 0.16 0.23 0.13 0.17 Extraction conditions: 10 cm x 0.25 mm i.d. microextrac tion capillary, 40 min extra ction time; Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted an alytes in the GC injector, 30 C 300 C, 5 min; GC oven te mperature rose from 30 to 300 C at rate of 20 C/min ; helium carrier gas; FID 350 C.

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108 Table 3.3 Detection limit data for PAHs, aldehydes, and ketones extracted from aqueous samples by CME GC using a sol gel germania PDMS coated microextraction capillary Analyte Cl ass Name Detectio n Limit (ng/L), (S/N =3) PAHs Aldehyde Ketones Naphthalene Fluorene Phenanthrene Pyrene Nonanal Decanal Undecanal Valerophenone Heptanophenone Hexanophenone Decanophenone 83.8 20.0 11.4 20.1 139.7 89.7 97 .7 92.3 46.1 35.8 30.6 Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, 40 min extra ction time; Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted analytes in the GC in jector, 30 C 300 C, 5 min; GC oven temperature rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C

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109 Capillary to capillary reproducibility is another important characteristic which shows the consistency of the method used to p repare the microextraction capillaries. In this work, we used one ketone, one aldehyde and a polycyclic aromatic hydrocarbon as test solutes for capillary to capillary reproducibility in CME performed on sol gel germania PDMS coated microextraction capilla ries (Table 3.4 ). For all the tested analytes, the peak area R.S.D. values for the extracted amounts were below 6%, which means germania based sol gel CME in conjunction with GC FID shows good reproducibility, and that the capillary preparation method poss esses acceptable consistency. Table 3.4 Capillary to capillary reproducibility (n=3) data for extracted amounts in CME GC experiments conducted on sol gel germania PDMS coated capillaries using a PAH (phenanthrene), an aldehyde (undecanal), and a ketone (h exanophenone) as test solutes Analytes Mean peak area (arbitrary unit) R.S.D. (%) Phenanthrene Undecanal Hexanophenone 27.9 3.5 13.2 5.4 5.5 5.9 Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, 40 min extra ction tim e; Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted an alytes in the GC injector, 30 C 300 C, 5 min; GC oven temperature rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C

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110 PAHs present potential health hazards because of their toxic, mutagenic, and carcinogenic properties. A chromatogram of PAHs obtained in a CME GC FID experiment using a sol gel germania PDMS coated CME capillary is presented in Figure 3. 3. Parts per trillion (ppt) level detection limits were achieved. Mention should be made here that, sol gel coating technology can easily produce stable coating with different thicknesses through manipulation of the in capillary residence time of the sol solu tion during preparation of the microextraction capillary. The use of microextraction capillaries with thicker coatings should provide higher sensitivity in CME [ 57 ]. Aldehydes and ketones also present health and environmental concerns. Polar nature of these carbonyl compounds often requires their derivatization prior to their extraction or chromatographic analysis [ 86 ]. In CME GC experiments, in which we used sol gel technology to prepare both the CME capillaries and GC columns, no derivatization step was necessary either for extraction or for GC analysis [ 57 87 ]. Sol gel germania PDMS capillary provided highly efficient extrac tion for aldehydes and ketones. As can be seen in Figure 3. 4 A and 3. 4 B, the GC peaks provided by the sol gel column are sharp and symmetrical, and this is indicative of effective focusing of the analytes at the GC column inlet after their desorption form the CME capillary, as well as excellent performance of the in lab prepared sol gel PDMS column used for GC separation. For both solute types, parts per trillion level detection limits were achieved.

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111 Figure 3. 3 CME GC trace analysis of a mixture of PAHs using a sol gel germania PDMS coated microextraction capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; oven t emperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C Peaks: (1) Naphthalene (2) Chrysene (3) Fluor ene (4) Phenanthrene (5) Pyrene

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11 2 Figure 3.4 A Figure 3.4 B Figure 3. 4 CME GC trace analysis of mixture of aldehydes and ketones using a sol gel germania PDMS coated microextraction capillary. Extraction Co nditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (gravity fed sample delivery at room temperature). Other conditions: 5 m x 0.25 mm i.d. Sol gel PDMS column; splitless analyte desorption by rapidly increasing the GC injecto r temperature from 30 C to 300 C, 5 min; GC oven temperature programmed from 30 C to 300 C at a rate of 20 C/min; helium carrier gas; FID 350 C; GC Peaks in 3.6 A: (1) Nonanal (2) Decanal (3) Undecanal (4) Dodecanal; GC Peaks in 3.6 B: (1)Valerophe none (2) Heptanophenone (3) Decanophenone (4) Anthraquinone

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113 Being highly polar compounds, alcohols demonstrate higher affinity for water and are usually difficult to extract from an aqueous matrix. In the present work, these highly polar analytes were extr acted from aqueous sample using sol gel germania APTMS coated capillary (Figure 3. 5) that did not require any analyte derivatization, pH adjustment, or salting out effect. Our results demonstrate that sol gel germania APTMS microextraction capillary has a pronounced affinity for these highly polar analytes. 3 9 .2 pH stability of sol gel germania PDMS coated capillary One serious shortcoming of conventional silica based statio nary phases and sorbents is their poor pH stability under both acidic and basic conditions. In this work, the pH stability of the prepared sol gel germania coated capillaries was evaluated by comparing the GC peak areas obtained in CME GC FID experiments c arried out on sol gel germania PDMS coated microextraction capillaries before and after prolonged treatment of the coated capillary surface under extreme pH conditions. Sol gel germania PDMS coating showed excellent pH stability. After coating and conditio ning, we conducted two sets of experiments in which we rinsed the sol gel germania PDMS capillaries for 24 hours with (a) 0.05M HCl and (b) 0.1M NaOH (pH=13). The results suggest that sol gel germania PDMS coating retain its excellent extraction capability after being subjected to prolonged rinsing with a strong base (Figure 3. 6) or a strong acid (Figure 3. 7). For example, after continuously rinsing a sol gel germania PDMS coated capillary for 24 hours with 0.1M NaOH, the GC peak areas for extracted amounts of phenanthrene and nonanal were found to increase by 5.0 % and 7.1 %, respectively. Similarly, after a continuous 24 hours rinse of the microextraction

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114 capillary with a 0.05 M HCl, the observed peak area changes for fluorene and heptanophenone were +4.1 % and +3.3 %, respectively. This data suggests that the new hybrid sol gel germania coated capillary has excellent pH stability. Rinsing with NaOH also led to improved extraction characteristics. For most solutes, after rinsing the capillary with NaOH, the peak area increa sed. In some instances, these increases were statistically significant and in other cases they were well within experimental errors. A significant increase in the peak area for some solutes can be explained by assuming that NaOH helps cleaning the sol gel germania PDMS coating by removing from its pores and surfaces various sorbed species that hinder the extraction process, and that getting rid of those sorbed species is often difficult via rinsing with commonly used organic solvent. 3.9. 3 Extraction of po lar compound s by Sol gel g ermania CME GC Chlorophenols are one of the major classes of environmental pollutants. Analytical capability to preconcentrate traces of these compounds in aqueous samples, therefore, presents significant interest in environmenta l science and technology. Figure 3. 8 shows an example highlighting the ability of a sol gel germania PDMDPS coated CME capillary to accomplish preconcentration of 2, 4, 6 triclorophenol a typical member of the chlorophenol family.

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115 Figure 3. 5 CME GC trace analysis of alcohols using a sol gel germania APTMS coated microextraction capillary. Extraction Conditions: 10 cm x 0.25 mm i.d. microextraction c apillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. Sol gel PDMS GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven t emperature programmed from 30 C to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C. GC peaks: (1) decanol (2) undecanol

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116 Figure 3. 6 A Figure 3. 6 B Figure 3. 6 Excellent stability of sol gel germania PDMS coating under highly basic conditions demonstrated through CME GC analysis of a mixture o f PAHs using a sol gel germania PDMS coated microextraction capillary before ( 3.6 A) and after ( 3.6 B) continuously rinsing the capillary with a 0.1 M NaOH solution (pH = 13) for 24h. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 30 min (Gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven te mperatur e rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C. GC peaks: (1) naphthalene, (2) fluorene, (3) phenanthrene, (4) pyrene

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117 Figure 3. 7 A Figure 3. 7 B Figure 3. 7 Excellent stability of sol gel germania PDMS coating under highly acidic conditions demonstrated through CME GC analysis of aldehydes using a germania PDMS coated microextraction capillary before ( 3.7 A) and after ( 3.7 B) continuously rinsing the capillary with a 0.05 M HCl solu tion for 24 h. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless desorption splitless an alyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven temperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C. GC peaks: (1) nonanal, (2) deca nal (3) undecanal (4) dodecanal

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118 Figur e 3. 8 CME GC trace analysis of 2, 4, 6 Trichlorophenol using a sol gel germania PDMDPS coated microextraction capillary. Extraction Conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption from the microextraction capillary by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven temperat ure programmed from 30 t o 300 C at rate of 20 C/min; helium carrier gas; FID 350 C. GC peak: (1) 2, 4, 6 Trichlorophenol

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119 In this example, a detection limit of 49.2 ppt was achieved for this chlorophenol in CME GC FID. Extraction of free fatty acids and their analysis by GC a re often met with serious analytical difficulties which can be explained by the presence of highly polar carboxyl group in the structure of these molecules and by the propensity of these molecules toward adsorption. To overcome these difficulties, analytic al chemists often derivatize these molecules to methyl esters and analyze the generated esters. However, quantitative derivatization of fatty acids especially when they are present in trace concentrations may be problematic. Figure 3. 9 presents a gas chrom atogram highlighting the possibility of extracting traces of free fatty acids from an aqueous medium using a sol gel germania APTMS coated CME capillary and direct GC analysis of free fatty acids using an in lab prepared sol gel PDMS open tubular GC column 3 9 .4 GC separation of sol gel germania PDMS coated column Gas chromatographic performances of a sol gel germania PDMS coated columns was investigated using a natural gas sample. Figure 3. 10 represents a chromatogram illustrating the possibility of analyzing a natural gas sample on a sol gel germania PDMS coated open tubular GC column. The symmetrica l and sharp peaks indicate the potential of sol gel germania PDMS coating for use as a stationary phase in GC, especially for low boiling analytes.

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120 Figure 3. 9 CME GC analysis of free fatty acids using a sol gel germania APTMS coated microextraction capillary. Extraction Conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (gravity fed at room t emperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption from the microextraction capillary by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; GC oven t emperature pr ogrammed from 30 C t o 300 C at rate of 20 C/min ; helium carrier gas; FID 350 C. GC peaks: (1) decanoic acid, (2) undecanoi c acid, and (3) dodecanoic acid

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121 Figure 3. 10 Gas chromatogram of a natural gas sample separated on sol gel germ ania PDMS stationary phase. Conditions: 5 m x 0.25 mm i.d. sol gel germania PDMS column; carrier gas, helium; injection, split (100:1, 300 C); FID 350 C, co nstant column temperature, 30 C. GC pe aks: (1) methane and (2) ethane

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122 3 10 Conclusion Germani a based sol gel organic inorganic hybrid coatings were developed for high performance capillary microextraction. Run to run and capillary to capillary reproducibility (peak area RSD) were below 6.5 % and 7.2 %, respectively. The developed method can be app lied to chemically bind non polar (e.g., PDMS), moderately polar (e.g., PDMDPS) and highly polar (e.g., APTMS) ligands to the sol gel germania network in the course of its evolution from the sol solution. The sol gel germania coated capillaries are effecti ve in extracting broad classes of analytes ranging from non polar PAHs to polar compounds such as alcohols and fatty acids. Parts per trillion level detection limits were achieved in CME GC FID using sol gel germania hybrid coatings for microextraction. So l gel germania PDMS coating also showed promising chromatographic performance as a GC stationary phase. To our knowledge, this is the first report on the use of sol gel germania hybrid coatings as sorbents in microextraction or as a GC stationary phase. 3 .11 Reference s for chapter three [ 1 ] S. K. Sharma, D. W. Matson, J. A. Philpotts, T.L. Rousch, J. Non Cryst. Solids, 68 (1984) 115 [ 2 ] M. Takahashi, H. Shigemura, Y. Kawamoto, J. Nishii, T. Yoko, J of Non Cryst. Sol. 259 (1999) 149 [ 3] N. Chiodini, F. Meinardi, F. Morazzoni, A. Paleari, R. Scotti, Phys. Rev. B. 60 (1999) 2429 [4] K. O. Hill, Y. Fujii, D. C. Johnson, B. S. Kawasaki, Appl. Phys. Lett. 32 (1978) 647 [5] U. Osterberg, W. Margulis, Opt. Lett., 11 (1986) 516

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124 [ 2 6] W. Que, W. Liu, X. Hu, Appl. Phys. B83 (2006) 295 [ 2 7] W. Que, L.L. Wang, T. Chen, Z. Sun, X. Hu, J. Cryst. Growth 288 (2006) 75 [ 2 8] W. Que, L.L. Wang, T. Chen, Z. Sun, X. Hu, J. Sol gel Sci. Technol 38 (2006) 147 [ 2 9] H. Kozuka, M. Kajimura, T. Hirano, K Katayama, J. Sol gel Sci. Technol 19 (2000) 205 [ 3 0] C B. Jing, J X Hou, Y H. Zhang, J. Phy s. D: Phys. 39 (2006) 1174 [ 3 1] B. Alonso, D. Massiot, F. Babonneau, G. Brusatin, G. D.Giustina, T. Kidchob, P. Innocenzi, Chem. Mater. 17 (2005) 3172 [ 32 ] Pawliszyn, J. Solid Phase Microextraction. Theory and Practice, Wiley, NY, 1997. [ 33 ] R. P. Belardi, J. Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179. [3 4 ] J. Krutz, S. A. Senseman, A. S. Sciumbato, J. Chromatogr. A 999 (2003) 103 [ 35 ] B. Zygmun t, A. Jastrzbska, J. Naminesnik, Crit. Rev. Anal. Chem. 31 (2001) 1 [ 36 ] F. Alpendurada, J. Chromatogr. A 889 ( 2000 ) 3 [ 37 ] S. Ulrich, J. Chromatogr. A 902 ( 2000 ) 167 [ 38 ] G. A. Mills, V. Walker J. Chromatogr. A 902 ( 2000 ) 267. [ 39 ] F. Augusto, A. L. P. Valente, Trends Anal. Chem. 21 ( 2002 ) 428 [ 40 ] H. Kataoka, H. L. Lord, J. Pawliszyn, J. Chromatogr. A. 880 (2000) 3 5 [ 41 ] T. Kumazawa, X. P. Lee, K. Sato, O. Su zuki, Anal. Chim. Acta 492 (2003) 49. [ 42 ] H. Kataoka, Tren ds Anal. Chem. 22 (2003) 2 32 [ 43 ] X P. Lee, T. Kumazawa, K. Sato, O. S uzuki, Chromatographia 42 (1996) 135. [ 44 ] G. Bentivenga, M. D'Auria, P. Fedeli, G. Mauriello, R. Racioppi, Int. J. Food Sci. Technol. 39 (2004) 1079. [ 45 ] K. Fytianos, N. Raikos, G. Theodoridis, Z. Velinova, H. Ts oukali, Chemosphere 65 (2006) 2090.

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125 [ 46 ] Y. Fan, Y. Q. Feng, J. T. Zhang, S. L. Da, M. Zhang, J. Chromatogr. A 1074 (2005) 9. [ 47 ] Z. Liu, J. Pawliszyn, J. Chromatogr. Sci. 44 ( 2006 ) 366. [ 48 ] C. Peres, C. Viallon, J. L. Berdague, Anal. Chem. 73 ( 2001 ) 1030 [ 49 ] Y. Z. Lou, M. J. Yang, J. Pawliszyn, J. High Resolu t. Chromatogr. 18 ( 1995 ) 727 [ 50 ] E. Baltussen, P. Sandra, F. David, C. Cramers, J. Microcolumn Sep. 11 ( 1999 ) 737 [ 51 ] J. A. Koziel, M. Odziemkowski, J. Pawliszyn, Anal. Chem. 73 ( 2001 ) 47. [ 52 ] I. Bruheim, X. Liu, J. Pawl iszyn, Anal. Chem. 75 ( 2003 ) 1002. [ 53 ] L. Nardi J. Chromatogr. A 985 (2003) 93 [ 54 ] R. Eisert, J. Pawliszyn, Anal. Chem. 69 (1997) 3140. [ 55 ] H. Hartmann, J. Burhenne, M. Spiteller, Fresenius Environ. Bull. 7 (1998) 96. [ 56 ] H. Kataoka, J. Pawliszyn, Chromatographia 50 (1999) 532. [ 57 ] S. Bigham, J. Medlar, A. Kabir, C. Shende, Alli, A. Malik, Anal. Chem. 74 (2002) 752. [ 58 ] K. D. Buchholz, J. Pawliszyn, Anal. Chem. 66 (1994) 160. [ 59 ] D. Louch, S. Motla gh, J. Pawliszyn, Anal. Chem. 64 (1992) 1187. [ 60 ] L. G. Blomberg J. Microcolumn Sep. 2 (1990) 62. [ 61 ] J. Yu, L. Dong, C. Wu, J. Xing, J. Chromatogr. A 978 (2002) 37. [ 62 ] K. D. Buchholz, J. Pawliszyn, Anal. Chem. 66 (1994) 160. [ 63 ] D. Wang, S. L. C hong, A. Ma lik, Anal. Chem. 69 (1997) 4566 [ 64 ] W. Li, D. P. Fries, A. Malik, J. Chromatogr. A 1044 (2004) 23. [ 65 ] J. de Zeeuw, J. Luong, Trends Anal. Chem. 21 (2002) 594. [ 66 ] B. Chankvetadze, C. Yamamoto, M. Kamigaito, N. Tanaka, K. Nakanishi, Y. Ok amoto, J. Chromatogr. A 1110 (2006) 46.

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126 [ 67 ] F. Li, H. Jin, R N. Fu, J L. Gu, G J. Lu Chin. Chem. Lett. 8 (1997) 793. [ 68 ] T A. Lin, G Y. Li, L K. Chau, Anal. Chim. Acta 576 (2006) 117. [ 69 ] Y L. Hu, Y L. Fu, G K. Li, Anal. Chim. Acta 567 (2006) 211. [ 70 ] S. Kulkarni, L. Fang, K. Alhoosh ani, A. Malik, J. Chromatogr. A 1124 (2006) 205 [ 71 ] A. Wehrli, J. C. Hildenbran d, H. P. Keller, R. Stampfli, R W Frei, J. Chromatogr. 149 (1978) 199. [ 72 ] J. Nawrocki, C. Dunlap, A. McCormick, P. W. Carr J. Chromat ogr. A. 1028 (2004) 1. [ 73 ] J. L. Glajch, J. J. Kirkland, J. Koehler J. Chromatogr. 384 (1987) 81. [ 74 ] D. V. McCalley, J. Chromatogr. A 902 (2000) 311. [ 75 ] K. Alhooshani, T. Y. Kim, A. Kabir, A. Mali k, J. Chromatogr. A 1062 (2005) 1 [76 ] T. Kim, K. Alhooshani, A. Kabir, D. P. Fries, A. Malik, J. Chromato gr. A 1047 (2004) 165 [ 77 ] M M Liu, Y. Liu, Z R Zeng, T Y. Peng J. Chromatogr. A, 1108 (2006) 149 [ 78 ] J. D. Hayes, A. Malik, J. Chromatogr. B 695 (1997) 3. [ 79 ] J. Hayes, A. Malik, Anal. Che m. 73 (2001) 987 [ 80 ] L. Armelao, M. Fabrizio, S. Gross, A. Martucci, E. Tondello, J. Mater. Chem. 10 (2000) 1147 [ 81 ] L. L. Hench, J. K. West, Chem. Rev. 90 (1990) 33. [ 82 ] Y. Guo, L. A. Colon Anal. Chem 67 (1995) 2511 [ 83 ] Y F. Mei, G G. Siu, X H. Huang, K W. Cheah, Z G. Dong, L. Fang, M. R. Sheng, X L. Wu, X M. Bao Phys. Lett. A 331 (2004) 248 [ 84 ] M. Seck, R. A. B. Devine, C. Hernandez, Y. Campidelli, J. C. Dupuy Appl. Phys. Lett. 72 (1998) 2748. [ 85 ] E. Iborra, J. Sangrador, M. Clement, J. Perrire Thin Solid Films 337 (1999) 253 [ 86 ] J. Nawrocki, I. Kalkowska, A. Dabrowska, J. Chromatogr. A 749 (1996) 157.

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127 [ 87 ] A. Kabir, C. Hamlet, A. Malik, J. Chromatogr. A 1047 (2004) 1.

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128 CHAPTER FOUR MIX ED GERMANIA SILICA SOL GEL CYANOPROPYL POLY(DIMETHYLSILOXANE) COATING FOR CAPILLARY MICROEXTRACTION OF POLAR ORGANIC TRACE CONTAMINANTS IN AQUEOUS MEDIA 4 1 Introduction Solid phase microextraction (SPME) [1 ] is an effective approach to sampling and sampl e preparation for both laboratory and field analyses. Developed in 1989 by Belardi and pawliszyn [ 2 ] SPME integrates sampling, sample preparation, analyte preparation, and sample introduction step to the analytical cycle providing a simple and efficient s olvent free method for the extraction and preconcentration of analytes from various sample matrices. A number of shortcomings inherent in traditional fiber SPME stem from design and physical construction of the fiber and syringe like SPME device. As one of the variants of SPME which has been proposed to overcome these difficulties [ 3 7 ] in tube SPME also called capillary microextraction, CME is promising, especially for effective hyphenation with liquid phase separation techniques [ 8 10 ]. The sorptive coat ing is the most important component fiber for both conventional SPME and in tube SPME, and its nature determines the fiber selectivity toward different compound classes. Polydimethylsiloxane (PDMS) phase was one of the first polymer s used in SPME [11] over the years. SPME has served as the most commonly used non polar coating [1 2 1 3 ]. Other polymeric coatings such as polyacrylate (PA) and

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129 carbowax (CW ) have been used to extract polar compound s for SPME. However, all these commercial ly available coatings pre sent important drawbacks such as their relative ly low thermal stability (200 C 270 C) and low organic solvent stability The lack of chemical bonding between the coating material and the substrate greatly restrained the hyphenation of SPME with HPLC. Sol gel coating technology has been shown to overcome these problems by synthesizing chemically bonded m i croextraction sorbents with different functional group s [1 4 1 6 ]. Sol gel chemistry offers an effective methodology to chemical incorporation of organic components into evolving inorganic polymeric structures under extraordinarily mild thermal conditions; therefore it provides a simple and efficient pathway to the synthesis of advanced material s for use as extraction sorbents. An important aspect directio n of this coating technology is that the selectivity of a sol gel coating can be easily fine tuned by changing the composition of the used sol solution. S ol gel chemistry was applied to prepare a number of coatings including polyethylene glycol (PEG) [1 7 ], hydroxyfullerene [1 8 ], and Crown ether [1 3 ] that provided extraction selectivity in SPME for both polar and non polar compounds. Silica based stationary phases and sorbents are dominantly used in modern separation and sample preparation techniques. Silic a surface chemistry and surface modification process are well understood. However, the limitations of siliceous materials are also well known. Under acidic pH conditions, coatings containing of siloxane bond s (Si O Si) become unstable [1 9 20 ] On the other hand, under a pH value of higher than 8, siloxane bond on the silica surface hydrolyzes [2 1 ] and it happens rapidly under elevated

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130 temperatures [2 2 ]. A number of methods such as multiple covalent bonds [2 3 ], multi dentate synthetic approach [2 4 ], and end capping [2 5 ] have been used to solve this problem. None of them, however, seems to work effectively. Therefore, developing sorbents with a wide range of pH stability is a fundamentally important area of research in chromatographic separation and sample pre paration Metal oxides such as zirconia, titania, and alumina are alternative materials to offer better chemical and thermal stabilities [2 2 ], and have attracted attention of separation scientists. The resultant metal oxide based sol gel stationary phases have been applied in separation science due to their superior pH stability and mechanical strength [2 2 ]. Besides, in recent years new research accomplishments have been made in the development and application of metal oxide based sol gel extraction sorbent s. T itania [2 6 2 8 ], zirconia [2 9 30 ] and alumina based [3 1 ] sol gel sorbents have been synthesized and applied in analytical microextraction. Results revealed that those materials offer better thermal and pH stability compared to silica based systems [2 6 2 7 2 9 3 1 ]. Our work focuses on developing organic inorganic hybrid sol gel coatings and monolithic beds [3 2 3 8 ] for various substrates such as capillary, fiber or particle surface to accomplish enhanced performance in analytical microextra c tion and sep aration. In past several years, we worked on titania and zirconia based sol gel systems that demonstrated high chemical and pH stabilities in applications involving CME in hyphenation with both GC and HPLC [2 6 2 9 ]. As an isostructural analogue of SiO 2 [3 9 ], GeO 2 is compatible with the silica network and they have similar properties. Tetramthyoxygermane (TMOG) [39], tetraethyoxygermane (TEOG) [4 1 ], tetrapropyloxygermane ( TPOG ) [4 2 ],

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131 germanium iso propoxide (TP i OG) [4 1 4 3 ], and ClGeCH 2 CH 2 COOH [4 4 ] etc ha ve been reported to introduce prepare mixed GeO 2 SiO 2 thin films [4 2 4 3 ], monolithic aerogel [ 40 ] and glasses [4 1 ] by sol gel technology. From a structural point of view, each Ge atom could be substitutional to a Si and be bonded to four O atoms, or it co uld be under coordinated giving rise to oxygen deficient centers (GODC) [4 5 ]. Those properties attracted considerable attention on its optical properties and optoelectronic applications [4 6 4 8 ]. Our preliminary research [3 2 ] has suggested that sol gel germ ania hybrid coatings not only have the ability to extract a wide range of analytes from aqueous media but also show ed outstanding solvent and pH stability which is difficult to achieve on pure silica based extraction material. Because of high affinity of w ater for highly polar compo unds, direct extraction of such analytes is difficult. S olution of this problem requires a highly polar extracting phase that can compete with water in term of polarity and provide a favorable environment for the transfer of high ly polar analytes from the aqueous medium into the extracting phase. Cyanopropyl based stationary phases provide extremely high chromatographic polarity [49]. Cyanopropylsiloxanes exhibit both polar and polarizable characteristics which are responsible for increased affi nity of these phases electrons. Cyano stationary phases have been used in GC and HPLC [ 50 5 2 ], capillary electrochromatography (CEC) [5 3] and as an extraction medium in solid phase extraction (SPE) [5 4 5 6 ]. Sol gel CN PDMS coating have been reported in our previous work [ 38 ]. The prepared cyano based sol gel coating provided highly stable performance at elevated temperature s compared with conventionally prepared cyano coatings (having no chemical bond s t o the substrate).

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132 Here we report on the development of cyanopropyl based sol gel germania hybrid coatings for the extraction of highly polar analytes from aqueous media 4 .2 Experimental 4 .2.1 Equipment Sol gel germania based c apillary microextraction g as chromatography (CME GC) experiments were carried out on a Shimadzu Model 14A GC system equipped with a flame ionization detector (FID) and a split/splitless injector. An in lab designed liquid sample dispenser was used to perform capillary microextracti on via gravity flow of aqueous samples through the sol gel microextraction capillary connected at the bottom end of the dispenser. A Fisher Model G 560 Genie 2 vortex (Fisher Scientific, Pittsburgh, PA) was used for thorough mixing of sol solution ingredie nts. A Micromax model 3590F microcentrifuge (Thermo IEC, Needham Heights, MA) was used for centrifugation at 14,000 rpm (15,682 x g) to separate out the precipitate from the sol solution. A home built gas pressure operated filling/purging device was used t o perform a number of operations: (a) filling the extraction capillary with the sol solution, (b) expelling the solution from the capillary after predetermined period of in capillary residence, (c) rinsing the capillary with a suitable solvent to clean the coated surface, and (d) purging a Barnstead Model 04741 Nanopure deionized water system (Barnstead/Thermodyne, Dubuque, IA). Online data collection and processing were accomplished using ChromPerfect (version 3.0) computer software (Justice Laboratory Software, Denville,

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133 NJ). 4 .2.2 Chemicals and materials Fused purchased from Polymicro Technologies Inc. (Phoenix, AZ). HPLC grade solvents (methanol, and tetrahydrofuran (THF)), were purchased from Fisher Scientific (Pittsburgh, PA). Valerophenone heptanophenone, hexanophenone, decanoic acid, undecanoic acid, dodecanoic acid nonanal, decana l, undecanal, 2,4,6 trichlorophenol and Pentachlorophenol, 1,1,1,3,3,3 hexamethyldisilazane, and formic acid (FA, 95%) were purchased from Aldrich (Milwaukee, WI). Hydroxy terminated polydimethylsiloxane (PDMS) was purchased from United Chemical Technologi es Inc. (Bristol, PA). Tetraethoxygermane (TEOG), 3 cyanopropyltriethoxysilane (CPTES) were obtained from Gelest, Inc (Morrisville, PA). 4 .2.3 Preparation of sol gel germanis CN/PDMS coated capillaries for CME The coating sol solution was prepared in a cle an polypropylene centrifuge tube T FA (with 38 % of water) and 5 min followed by centrifugation for 4 min to remove possibl e precipitates. The clean supernatant was transferred gently to another clean vial. A hydrothermally pretreated fused silica capillary (1 m) was filled with the clear sol solution using pressurized helium (40 psi) in a filling/purging device. The sol solut ion was allowed to stay inside the capillary for 40 min to facilitate the formation of a sol gel coating. During this in capillary residence period, a 3 dimensional sol gel network was formed in the sol

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134 solution due to hydrolytic polycondensation reactions During this process, patches of the sol gel network evolving in the vicinity of the capillary inner surface got chemically bonded to the capillary walls due to condensation reactions between the sol gel active groups on the sol gel network fragments and the silanol groups on the surface of fused silica capillary. Following this, the capillary was purged with helium (50 psi) for an hour to expel the unbonded portion of the sol solution leaving behind a dry surface bonded sol gel coating on the capillary in ner walls. The capillary was further conditioned under helium purge by programming the temperature from 40 C to 250 C at 1 C/min and held at the final temperature for 4 hours. The sol gel coated microextraction capillary was then rinsed with a 1:1 (v/v) mixture of methylene chloride and methanol (2 mL), and then the capillary was conditioned again from 40 C 250 C at 5 C/min, from 250 C to 300 C at 1 C/min and held at final temperature for 1 hour. The conditioned capillary was then cut into 10 cm long pieces that were ready for use in capillary microextraction. 4 .2.4 Preparation of aqueous samples for CME GC Solute standards were first dissolved in methanol or THF to obtain the stock solutions (10 mg/mL), which was further diluted to 0.1 mg/mL in the same solvent and stored in the freezer in amber vials The fresh aqueous sample was prepared daily by further diluting this solution with DI water. All the glassware used was deactivated by treating with HMDS solution to avoid analyte loss due to adsor ption on the glassware surface.

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135 4 .2.5 Sol gel capillary microextraction by an in lab gravity fed sample dispenser An in lab designed gravity fed sample dispenser was used for capillary microextraction. It was constructed by modifying a Chromaflex AQ col umn (Kontes Glass Co., Vineland, NJ) consisting of a thick walled Pyrex glass cylinder concentrically placed in an acrylic jacket. The inner surface of the glass cylinder was deactivated as described previously [57]. In lab dispenser provided a consistent means to pass the liquid through the microextraction capillary under gravity. Therefore, it provides a convenient means for (1) the flow through microextraction to take place and (2) cleaning or rinsing the inside of the capillary. A 10 cm long segment of previously conditioned cyanopropyl based sol gel bottom end of an empty sample dispenser. A 50 mL volume of the aqueous sample solution was then filled into the dispenser, and the sample solution was allowed to f low through the microextraction capillary under gravity. During this flow through process, the analyte molecules were extracted by the sol gel germania hybrid coating residing on the inner walls of the capillary. With the progression of this microextractio n process, an equilibrium was established between the sol gel sorbent coating and the sample solution (typically within 30 40 min). The capillary was then removed from the sample dispenser, briefly purged with helium, and connected to the inlet end of the GC column using a two way press fit connector. The free end of the microextraction capillary was introduced into the GC injection port (from the bottom end of the port previously cooled down to 30 C) so that ~8 cm of the capillary resided inside the quart z liner in the injection port. A

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136 graphite ferrule was used to secure a leak free connection between the capillary and the lower end of injection port. The extracted analytes were then thermally desorbed from the capillary in the splitless injection mode by rapidly raising the temperature of the injector (from 30C to 300C in five min) and the desorbed analytes were transported to the GC column by the helium flow through the injector. The desorbed analytes were focused at the inlet of the GC column held at 30 C. Analyte desorption and focusing was performed over a 5 min period. The GC column temperature was then raised @ 20 C/min to facilitate transportation of the focused solutes through the column providing their GC separation. A flame ionization detecto r (FID), maintained at 350 C, was used for analyte detection. The PDMS based sol gel GC silica based sol gel capillary column was also prepared in house following the procedure described by us elsewhere [3 2 ]. 4 3 Results and discussion 4 .3.1 Chemical rea ctions involved in the preparation of sol gel Germania CN/PDMS coatings Table 4. 1 lists the chemical ingredients used in the sol solution to in situ create germania based sol gel hybrid organic inorganic coatings within fused silica capillaries for us e in solvent free microextraction. All the chemicals presented in table 4. 1 except catalyst were dispersed and thoroughly mixed in solvent(s) first, and the catalyst w as introduced at the end to initiate the sol gel process. Sol gel process consists of two main reactions : (1) hydrolysis of the precursor(s) and (2) polycondensation of hydrolyzed the sol gel active species present in the sol solution. Silica base sol gel system is the most widely used, however, analogous non silica material such as those base d on zirconia

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137 titania and alumina have already been prepared [22, 26, 29, 58] Since GeO 2 is well established as an isostructural analog of SiO 2 it is compatible with the silica network [39]. Our previous work [32], germanium alkoxide precursor has bee n successfully used in conjunction with hydroxyl terminated polysiloxanes to prepare Germania based sol gel extraction for CME as well as Ge stationary phase TEOG served as the sol gel precursor and generated the inorganic component of the resulting hybri d sol gel organic inorganic coating. The hydroxy terminated PDMS, CPTES served as the source of the organic component of the hybrid coating CPTES played a dual role: it served as a sol gel co precursor and also served as the source of the organic (cyanopr opyl) ligands providing the cyano functional group to the system. B ecause of the high thermal stability and good film forming performance of PDMS a small amount hydroxy terminated PDMS was incorporated in the sol solution to help for the formation of stab le the sol gel coating

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138 Table 4. 1 Chemical ingredients of the coating solution used in preparing sol gel germania organic inorganic hybrid coatings chemically anchored to the inner surface of a fused silica capillary Ingredient Function Chemical s tructure Tetraethoxygermane (TEOG) Hydroxy terminated polydimethylsiloxane (PDMS) 3 Cyanopropyltriethoxysilane (CPTES) Methanol Formic acid (96%) Water Sol gel precursor Sol gel active polymer Sol gel active polymer Solven t Catalyst Hydrolysis reagent H 2 O

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139 The creation of sol gel hybrid germania coatings involved the following chemical processes: (1) hydrolysis of the alkoxide based precursors ( S cheme 4. 1), (2) polycondensation of the partially and/or fully hydrolyzed precursors among themselves and with other sol gel active components of the solution ( S cheme 4. 2), (3) chemical bonding of hydrolyzed CPTES and hydroxyl terminated PDMS to the evolving sol gel germania network, and (4) chemical anchoring of the evolving hybrid organic inorganic polymer to the inner walls of the capillary ( S ch eme 4. 3). The hydrolysis (partial or complete) of TEOG produces a variety of reactive hydroxyl containing species which are capable of undergoing condensation reactions with neighboring sol gel active chemical species in the sol solution such as CPTES and hydroxyl terminated PDMS Condensation of these reactive species leads to a hybrid organic inorganic network via chemical integration of an inorganic component (germania, originating from TEOG) and a cyanopropyl containing organic residual (cyanopropyl h ydrolyzed forms of CPTES). Addition of PDMS into the system promoted the network form ation and incorporation and bridging of the chemical species arising from hydrolysis of TEOG, CPTES. The silanol groups residing on the inner walls of the fused silica cap illary are also sol gel active and under the catalyst they can take part in the condensation reactions with the sol gel network fragments in their vicinity resulting in chemical anchoring of a portion of the sol gel material on the surface of the capillary walls. This portion of surface bonded sol gel material is left on the capillary surface in the form of an organic inorganic hybrid coating and serve d as the sorbent for solvent free microextraction. After coating and thermal conditioning, the capillary wa s rinsed with a mixture of methylene chloride and

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140 methanol to get rid of unreacted chemical species physically adhering to the coating. Sol gel hybrid germania coated capillaries were then ready for microextraction. 4 .3.2 Extraction p rofiles for sol gel ge rmania CN/PDMS capillaries In capillary microextraction, it is desirable that the extraction equilibrium is reached in the shortest possible time. In this work, we investigated the relationship between extraction time and the amount of analytes extracted i n CME with sol gel germania CN/PDMS coating (Figure 4. 1). As can be seen in F igure 4. 1, for undecanol, the extraction equilibrium was reached within 20 min. For pentachlorophenol, a highly polar solute, the time to reach equilibrium was around 30 min. Howe ver, for heptanophenone, which is moderately polar compound compared with phenols and alcohols, the time to reach equilibrium wa s at 40 min. These results indicated that polar solutes present stronger affinity to the developed polar germania CN/PDMS coatin g, which makes sorption time for them shorter. Based on this observation, 40 min extraction time was used in CME experiments presented in this paper. Scheme 4. 1 Hydrolysis of germania precursor (TEOG)

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141 Scheme 4. 2 Polycondensation of the hydrolyzed precursor and chemical bonding of the sol gel active organic ligand (Y) to the evolving sol gel network

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142 Scheme 4. 3 Chemical anchoring of the evolving sol gel germania hybrid o rganic inorganic polymer to the inner walls of a fused silica capillary

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143 Figure 4. 1 Capillary microextraction profiles of undecanol, heptanophenone, pentachlorophenol on a sol gel germania CN/PDMS coated capillary. Extraction conditions: 10 cm x 0.25 mm i .d. microextraction capillary, gravity fed sample dispenser for extraction at room temperature. Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature fr om 30 C to 300 C, 5 min; GC oven temperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C.

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144 4 .3.3 Extraction characteristics of sol gel germania CN/PDMS in CME Aqueous samples of different classes of analyte s (ketones, alcohols, acids, and phenols) were used. GC peak areas obtained from the extracted analytes were used as a measure of the extracted amounts in CME. As can be see n from T able 4. 2, the peak area run to run R.S.D values for phenol samples were un der 3.18 %, and those for GC retention times were less than 0.2 %. For ketones, the RSD values for run to run peak area and GC retention time were under 6.89 % and 0.07 % respectively. For acids and alc o hols, the run to run peak area R.S.D value were und er 4.51 %, 3.52 % and that for retention time s were within 0.07, and 0. 54 % respectively U sing the developed sol gel germania hybrid coatings for capillary microextraction ng/L level detection limits were achieved in CME GC FID for most analytes The d etection limit value for different classes of analytes is shown in Table 4. 3. Capillary to capillary reproducibility is another important criterion to characterize the consistency in capillary preparation. The results are presented in Table 4. 4 For each analyte, extractions were made in triplicates on each capillary and the mean of the measured peak areas were used in Table 4. 4 to evaluate capillary to capillary reproducibility. The presented data show ed that the capi llary to capillary reproducibility is characterized by an RSD value of less than 5.5 % for all four classes of compounds used for evaluation T he low RSD value is indicative of excellent reproducibility.

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145 Table 4. 2 GC p eak area and retent ion time repeatability data (n= 4 ) for chlorophenols, alcohols, free fatty acids and ketones extracted from aqueous samples by CME using sol gel germania CN/PDMS coated microextraction capillary Analyte Peak area repeatability (n=4) t R Repeatability (n=4) Class Name Mean peak area (aribitary unit) R.S.D. (%) Mean t R (min) R.S.D. (%) Ketoens Phenols Acids Alcohols Valerophenone Hexanophenone Heptanophenone 2,3 dichlorophenol 2,4,6 trichlorophenol Pentachlorophenol Decanoic acid Undecanoic acid Nonanol Decanol Undecanol 3 .5 9 .6 24 .5 7.9 10.1 20.1 3.0 8.0 4.4 15.3 29.7 6.89 3.75 3.50 3.18 1.84 2.21 4.26 4 .51 3.52 1.81 1.61 8.40 9.10 9.77 7.52 8.76 8.89 8.65 9.29 6.7 0 7.49 8.23 0.07 0.06 0.06 0.20 0.06 0.19 0.07 0.0 5 0.54 0.28 0.19 Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, 40 min extraction time; Other conditions: 1 0 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted an alytes in the GC injector, 30 C 300 C, 5 min; GC oven te mperature rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C

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146 Table 4. 3 GC FID d etection limit data (n=4) for chlorophenols, alcohols, free fatty acids and ketones extracted from aqueous samples by CME using sol gel germania CN/PDMS co ated microextraction capillary Analyte Class Name Detection Limit (ng/L) Keto ens Phenols Acids Alcohols Valerophenone Hexanophenone Heptanophenone 2,3 dichlorophenol 2,4,6 trichlorophenol Pentachlorophenol Decanoic acid Undecanoic acid Nonanol Decanol Undecanol 185.7 30.6 25.4 226.6 187.5 105.0 227.9 250.9 387.9 115.8 20.0 Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, 40 min extraction time; Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted analytes in the GC injector, 30 C 300 C, 5 min; GC oven te mperature rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 350 C

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147 Table 4 .4 Capillary to capillary repr oducibility (n=3) data for extracted amounts in CME GC experiments conducted on sol gel germania CN/PDMS coated capillaries using a chlorophenol (pentachlorophenol), an alcohol (undecanol), a free fatty acid (undecanoic acid) and a ketone (hept anophenone) as test solutes Analytes Mean peak area (arbitrary unit) R.S.D. (%) Hepanophenone Undecanol Undecanoic acid Pentachlorophenol 23.9 29.1 5.8 11.9 1.4 2.4 1.5 5.8 Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, 40 min extraction tim e; Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS open tubular GC column; splitless desorption of the extracted analytes in the GC injector, 30 C 300 C, 5 min; GC oven te mperature rose from 30 to 300 C at rate of 20 C/min; helium carrier gas; FID 35 0 C

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148 Being polar compounds, alcohols demonstrate higher affinity for water and are usually difficult to extract from an aqueous matrix. In the present work, th is class of analytes were extracted from aqueous sample using sol gel germania C N/PDMS coated capillary (Figure 4. 2) that did not require any analyte derivatization, pH adjustment, or salting out effect. From the Figure 4. 2, germania C N /PDMS showed excellent extraction ability to alcohols T he introduction of PDMS help ed incorporate CPTES into the germania based sol gel material because of the excellent netw ork forming properties of PDMS. On the other hand, CPTES provided cyano polar functional groups into the system, which possess stronger affinity to polar compounds. Compared with our pre vious germania PDMS [3 2 ], the introduction of small polar precursor such as CPTES provide s sol gel Germania coatings capability of extracting polar analytes from aqueous media. Extraction of free fatty acids and their analysis by GC is always difficult due to the presence of highly polar carboxyl group in the structure of these molecules and the propensity of these molecules toward adsorption. Therefore these molecules are o ften derivatized to methyl esters and the generated esters are subsequently analyzed which is time consuming. Besides quantitative derivatization of fatty acids in trace concentrations may be problematic. A ll these drawbacks of traditional approaches for the analysis of fatty acids can be avoided by using cyanopropyl based sol gel Germania coatings In this work, sol gel germania CPTES coatings were used to extract free fatty acids from an aqueous medium (Figure 4. 3).

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149 Figure 4. 2 CME GC analysis of a mixture of alcohols using a sol gel ger mania CN/PDMS coated microextraction capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; oven t emperature programmed from 30 C to 300 C at a rate of 20 C/min; helium carrier gas; FID 350 C Peaks: (1) Nonanol (2) Decanol (3) Undecano l

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150 Chlorophenols (CPs) are one of the m ajor classes of environmental pollutants constitutes an important group of priority toxic pollutants listed by EPA, with possible carcinogenic properties. Chlorophenols (CPs) have been widely used as preservatives, pesticides, antiseptics, and disinfectant s [59 ], and they are often found in waters [ 60 ], soils, and sediments [ 61 ]. CPs are highly polar compounds with significant affinity toward water. In our study, four CPs were extracted from water samples using germania based CN PDMS coated capillaries. Low detection limits of ng/L level were achieved. Figure 4. 4 shows an example of excellent the ability of a sol gel germania CN/PDMS coated CME capillary to accomplish preconcentration of some chlorophenols. Ketones are relatively less polar compared with above classes of compounds, and present health and environmental concerns. 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. However, it often requires their derivatization prior to their extraction or chromatographic a nalysis In sol gel germania based CME GC experiments (Figure 4. 5), no derivatization step was necessary either for extraction or GC analysis of ketone samples

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151 Figure 4. 3 CME GC analysis of a mixture of acid s using a sol gel germania CN/PDMS coated microextraction capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; oven t emperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C Peaks: (1) Decanoic ac id (2) Undecanoic acid (3) Dodecanoic acid

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152 Figure 4 .4 CME GC analysis of a mixture of chlorophenols using a sol gel germania CN/PDMS coated microextraction capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction tim e, 40 min (Gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector tempe rature from 30 C to 300 C, 5 min; oven t emperature programm ed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C Peaks: (1) 2,4,6 trichlorophenol (2) Pentachlorophenol

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153 Figure 4. 5 CME GC analysis of a mixture of ketones using a sol gel germania CN/PDMS coated microextraction capillary. Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 5 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte de sorption by rapidly increasing the GC injector temperature from 30 C to 300 C, 5 min; oven t emperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C Peaks: (1) Valerophenone (2) H exanophenone (3) Heptanophenone

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154 4 .3.4 Thermal stability of sol gel germania coatings in CME Sol gel germania CN/PDMS coating showed excellent thermal stability. After coating and conditioning, the conditioning temperature was stepwise increased from 250 C to 350 C with an interval of 20 C. At each temperature, the capillary was conditioned for one hour. The experimental peak area data obtained after conditioning the capillary at each temperature were compared. In Figure 4. 6 present the extraction performance of the sol gel germania CN/PD MS coated capillary was studied for nonanol (an alcohol ) in the course of stepwise conditioning of the capillary The results suggest that sol gel germania CN/PDMS coating retain its excellent extraction capability after being conditioned at 3 3 0 C.

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155 Figure 4. 6 Effect of conditioning temperature o n the performance of sol gel g ermania CN / PDMS microextraction capillary in the extraction of nonanol Extraction conditions: 10 cm x 0.25 mm i.d. microextraction capillary, extraction time, 40 min (Gravity fed at room temperature). Other conditions: 10 m x 0.25 mm i.d. sol gel PDMS coated GC capillary column; splitless analyte desorption by rapidly increasing the GC injector t emperature from 30 C to 300 C, 5 min; oven temperature programmed from 30 C to 300 C at a rate of 20 C/min ; helium carrier gas; FID 350 C Peaks.

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156 4 4 C onclusion A cyanopropyl based sol gel g ermania organic inorganic hybrid coating was developed for the preconcentration of polar analytes from aqueous by capillary microextraction T he developed coating was prepared by us ing two different precursors TEOG (germania component) and CPTES (silica component) and a small amount of PDMS. PDMS is a non polar polymer. The sol gel geamania PDMS capillary reported in previous work only showed ex cellent affinities for nonpolar and moderately polar compounds. However, the sol gel germania CN/PDMS capillary was effective in extracting polar analytes such as alcohols, fatty acids, and phenols, because presence of high polar cyanopropyl ligands. Good run to run and capillary to capillary reproducibility (peak area RSD) was achieved for most polar analytes (below 7 %) and ng/L level detection limits were achieved in CME GC FID for most analytes, using the developed sol gel germania hybrid coatings for c apillary microextraction. The developed sol gel germania CPTES/PDMS capillary also showed excellent thermal stability, due to the chemical anchoring of such polar coatings onto the fused silica surface 4 5 Reference s for c hapter f our [1] J. Pawliszyn, So lid Phase Microextraction. Theory and Practice, Wiley, NY, 1997 [2] R. P. Belardi, J. Pawliszyn, Water Pollut. Res. J. Can. 24 (1989) 179. [3] Y. Z. Lou, M. J. Yang, J. Pawliszyn, J. High Resolut. Chromatogr. 18 (1995) 727. [4] E. Baltussen, P. Sandra, F. David, C. Cramers, J. Microcolumn Sep. 11 (1999) 737. [ 5] J. A. Koziel, M. Odziemkowski, J. Pawliszyn, Anal. Chem. 73 (2001) 47.

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160 APPENDICES

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ABOUT THE AUTHOR degree in Chemistry Education from Anhui Normal University in 20 00. She continued her studies at University of Science and Technology of China (Hefei, Anhui) and received her Master of Science degree in Analytical Chemistry in 2003. Later, she came to United States and joined the Department of Chemistry, University of South Florida to pursue a Doctorate Degree. The work presented here was conducted under the guidance of Dr. Abdul Malik. S he has three publications in international journals.