DEVELOPMENT OF MINIATURIZED SAMPLE PREPARATION APPROACHES XU LI NATIONAL UNIVERSITY OF SINGAPORE 2009 DEVELOPMENT OF MINIATURIZED SAMPLE PREPARATION APPROACHES by XU LI (M.Sc., WUHAN UNIVERSITY) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2009 ACKNOWLEDGEMENTS First of all, I would like to express my deepest gratitude to my supervisor, Professor Lee Hian Kee, for his invaluable advice, guidance, unconditional support and encouragement during the period of this research. From him I have learnt how to overcome the difficulties in research and how to carry out research work independently. I am also thankful to the Associate Professor Peter C. Hauser of University of Basel. I appreciate his guidance and help when I was in his group as an exchange student. I would also like to extend my special thanks to Mdm Lim Guek Choo, Dr Liu Qi Ping and many other laboratory officers of the Department of Chemistry for their kind help and assistance. I appreciate their support of my laboratory colleagues, Dr Chanbasha Basheer, Dr Zhang Jie, Dr Wu Jingming, Mr Hii Toh Ming, Mr Guo Liang, Ms Lee Jingyi and many other colleagues I may neglect to mention here. The financial support provided by the National University of Singapore in the form of a research scholarship is greatly acknowledged. In addition, the financial support provided by Swiss Federal Commission for Foreign Students (ESKAS) is also acknowledged. i Table of Contents Acknowledgements i Table of Contents ii Summary viii List of Tables . xii List of Figures xiii Nomenclatures . xvi Chapter Introduction .1 1.1 Sample preparation 1.2 Sorbent phase-based microextraction (SPBME) .3 1.2.1 Different modes of SPBME 1.2.1.1 F iber-based solid-phase microextraction ( SPME) .3 1.2.1.2 In-tube SPME .4 1.2.1.3 Stir-bar sorptive extraction (SBSE) .6 1.2.1.4 Microextraction in a packed syringe (MEPS) .7 1.2.1.5 Micro-solid-phase extraction (µ-SPE) .8 1.2.1.6 Thin film microextraction 1.2.1.7 Polymer-coated hollow fiber membrane microextraction (PC-HFME) .9 1.2.2 Novel materials applicable to the sorbent phase of SPBME 1.2.2.1 Imprinted materials 10 1.2.2.2 Nanomaterials 14 1.2.2.2-1 Carbon nanotubes (CNTs) 14 1.2.2.2-2 Nanoparticles 16 1.2.2.3 Ionic liquids (ILs) .19 1.2.2.4 Ordered mesoporous materials 21 1.2.2.5 Hybrid materials 23 1.3 Liquid-phase microextraction (LPME) 25 1.3.1 Carrier-mediated LPME (Ion-pair LPME) 27 ii 1.3.2 Electro membrane isolation (EMI) .28 1.3.3 Dynamic LPME .29 1.3.4 Single-drop microextraction (SDME) .30 1.3.5 Dispersive liquid-liquid microextraction (DLLME) .34 1.3.6 Continuous-flow microextraction (CFME) .35 1.3.7 Solvent-bar microextraction (SBME) 36 1.4 This work: Objective and organization 37 Chapter 2. Zirconia Hollow Fiber: Preparation, Characterization, and Application to Microextraction 40 2.1 Introduction 40 2.2 Experimental 43 2.2.1 Reagents and materials .43 2.2.2 Preparation of zirconia sol 43 2.2.3 Preparation of ZHF .44 2.2.4 Characterization of ZHF .44 2.2.5 Extraction procedure 46 2.2.6 LC-MS analysis .47 2.2.7 Application to lake water 47 2.3 Results and discussion .48 2.3.1 Preparation of ZHF .48 2.3.2 Characterization of ZHF .51 2.3.3 Optimization of extraction performance 55 2.3.4 Validation 58 2.3.5 Analysis of lake water .60 2.4 Conclusions 60 Chapter 3. Preparation, Characterization and Analytical Application of A Hybrid Organic-Inorganic Silica-Based Monolith .62 3.1 Introduction 62 3.2 Experimental 64 3.2.1 Regents and materials .64 iii 3.2.2 Apparatus 65 3.2.3 Preparation of the hybrid monolith 66 3.2.4 Characterization of the hybrid silica monolith .67 3.2.5 Oxidization of the hybrid silica monolith 67 3.2.6 Sample preparation .67 3.2.7 Application: in-tube microextraction process .68 3.3 Results and discussion .68 3.3.1 Optimization of synthetic conditions for the hybrid monolith 68 3.3.1.1 The influence of solvent .70 3.3.1.2 The influence of amount of PEG 71 3.3.1.3 The influence of gelation temperature .73 3.3.1.4 The influence of catalyst 74 3.3.1.5 The influence of reactant ratio (TMOS/MPTS) 75 3.3.2 Characterization of the hybrid silica monolith .76 3.3.3 Optimization of in-tube microextraction .80 3.3.4 Validation 81 3.3.5 Application 82 3.4 Conclusions 83 Chapter 4. Novel Approach to Microwave-Assisted Extraction and Micro-Solid-Phase Extraction from Soil Using Graphite Fibers as Sorbent 85 4.1 Introduction 85 4.2 Experimental 88 4.2.1 Chemicals and reagents 88 4.2.2 GC-FID and GC-MS analysis .88 4.2.3 SEM .89 4.2.4 Sample preparation .89 4.2.5 MAE 89 4.2.6 Sonication-assisted desorption .90 4.2.7 Sonication-assisted extraction (SAE) and agitation-assisted extraction (AAE) .90 iv 4.3 Results and discussion .91 4.3.1 Properties of a graphite fiber 91 4.3.2 Optimization of MAE-µ-SPE 92 4.3.3 Comparison .96 4.3.4 Method evaluation 98 4.3.5 Applications 101 4.4 Conclusions 101 Chapter Solvent Bar Microextraction of Herbicides Combined with Non-Aqueous Field-Amplified Sample Injection Capillary Electrophoresis 103 5.1 Introduction 103 5.2 Experimental 106 5.2.1 Reagents and materials .106 5.2.2 Instrumental 107 5.2.3 Online preconcentration procedure 108 5.2.4 Microextraction procedure 109 5.3 Results and discussion .109 5.3.1 Optimization of NACE separation conditions .109 5.3.1.1 Effect of electrolyte concentrations on separation .111 5.3.1.2 Effect of different organic solvents composition on separation .112 5.3.2 Online preconcentration procedure 115 5.3.2.1 Effect of sample injection volume on stacking efficiency .115 5.3.2.2 Effect of different organic solvents as pre-introduced plugs on stacking efficiency 116 5.3.2.3 Effect of pre-introduced organic solvent plug lengths on stacking efficiency 119 5.3.3 Optimization of SBME 120 5.3.3.1 Selection of organic solvent for extraction 121 5.3.3.2 Effect of sample solution pH 123 5.3.3.3 Extraction time .124 5.3.3.4 Stirring speed .125 v 5.3.3.5 Effect of salt addition on SBME .125 5.3.4 Comparison of extraction efficiency amongst HF/LPME, SBME and SDME .126 5.3.5 Validation 127 5.4 Conclusions 129 Chapter Liquid-liquid-liquid Microextraction of Nerve Agent Degradation Products Followed by Capillary Electrophoresis with Capacitively-Coupled Contactless Conductivity Detection 131 6.1 Introduction 131 6.2 Experimental 132 6.2.1 Chemicals and reagents 132 6.2.2 Instrumental 133 6.2.3 Sample preparation .134 6.2.4 Ion-Pair-LLLME procedure 135 6.2.5 EMI procedure 136 6.3 Results and discussion .136 6.3.1 CE-C4D of nerve agent degradation products with large-volume sample injection (LVSI) 136 6.3.2 Ion-pair-LLLME .138 6.3.2.1 Selection of ion-pair reagent 138 6.3.2.2 Selection of organic solvent (transferring phase) 139 6.3.2.3 Influence of the concentration of the ion-pair reagent on the extraction efficiency 140 6.3.2.4 Influence of the pH value of the donor phase 141 6.3.2.5 Influence of the pH value of the acceptor phase on the extraction efficiency 143 6.3.2.6 Influence of the stirring speed on the extraction efficiency .144 6.3.2.7 Extraction time .145 6.3.2.8 Validation .146 6.3.2.9 Spiked river water sample 147 vi 6.3.3 EMI .147 6.3.3.1 Selection of organic solvent- supported liquid membrane (SLM) .148 6.3.3.2 Influence of voltage 150 6.3.3.3 Influence of stirring speed .152 6.3.3.4 Extraction time profile .153 6.3.3.5 Influence of pH of the acceptor and donor phase 154 6.3.3.6 Method evaluation with an optimized condition 155 6.3.3.7 Spiked river water sample analysis 156 6.4 Conclusions 159 Chapter Conclusions and Outlook 161 References .164 List of Publications 185 vii SUMMARY This dissertation strikes at the heart of one of the major challenges associated with sample preparation, developing miniaturized and environmental-friendly microextraction methodologies. The work described involves the development of novel functional materials for solid-phase microextraction, and exploration of liquid-phase microextraction system for interesting analytes of environmental concern. A zirconia hollow fiber (ZHF) membrane, was for the first time successfully synthesized via a templating method coupled with sol-gel process. The resulting hollow fiber membrane exhibits a hollow core structure and has a bimodal porous substructure, narrowly-distributed nano skeleton pores and uniform textural pores or throughpores. This ZHF was applied for the purification and concentration of a nerve agent degradation product followed by high performance liquid chromatography (HPLC)-mass spectrometry (MS) analysis. Since the ZHF exists as an individual device and is directly usable for extracting, handling is more convenient. Pinacolyl methylphosphonic acid (PMPA), one type of organophosphorus nerve agent degradation product, was used as the model analyte. 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Hauser, Ion-Pair Liquid-liquid-liquid microextraction of nerve agent degradation products followed by capillary electrophoresis with contactless conductivity detection, J. Chromatogr. A 1205 (2008) 158. [6] Li Xu, Peter C. Hauser, Hian Kee Lee, Electro membrane isolation of nerve agent degradation products across a supported liquid membrane followed by capillary electrophoresis with contactless conductivity detection, J. Chromatogr. A 1214 (2008) 17. [7] Li Xu, Chanbasha Basheer, Hian Kee Lee, Chemical reactions in liquid-phase microextraction, J. Chromatogr. A 1216 (2009) 701. [8] Li Xu, Hian Kee Lee, Solvent-bar microextraction-Using a silica monolith as the extractant phase holder, J. Chromatogr. A 1216 (2009) 5483. [9] Li Xu, Peter C. Hauser, Hian Kee Lee, Determination of nerve agent degradation products by capillary electrophoresis using field-amplified sample stacking injection with the electroosmotic flow pump and contactless conductivity detection, J. Chromatogr. A 1216 (2009) 5911. [10] Li Xu, Hian Kee Lee, Sulfonated polyvinyl chloride fibers for cation-exchange microextraction, J. Chromatogr. A 1216 (1009) 6549. 185 [11] Li Xu, Chanbasha Basheer, Hian Kee Lee, Solvent-bar microextraction of herbicides combined with non-aqueous field-amplified sample injection capillary electrophoresis, under preparation. [12] Z. Shi, L. Xu, H.K. Lee, Book chapter, “silica monoliths in solid-phase extraction and solid-phase microextraction” (Editors: E. Machtejevas, N. Tanaka, K.K. Unger, Monolithic silicas-Concepts, syntheses, characterization, modeling and applications in liquid phase separations). 186 [...]... images of ZHF and PHF: (a) cross-sectional image of ZHF; (b) longitudinal image of ZHF; (c) textural image of ZHF; (d) textural image of PHF; (e) nanopores of ZHF; (f) fibrous structure of PHF Figure 2-5 Influence of sample solution pH on the extraction efficiency Figure 2-6 Extraction time profile Figure 2-7 Desorption time profile Figure 2-8 LC–MS total ion chromatograms: (a) ZHF-extract of deionized... 4) bupicaine Figure 4-1 SEM of a single graphite fiber xiii Figure 4-2 Influence of heating temperature on MAE efficiency Figure 4-3 Time profile of MAE of PAHs Figure 4-4 Time profile of elution of PAHs Figure 4-5 Comparison of different methods and materials GF=graphite fiber; AC =activated carbon Figure 5-1 Effect of ammonium acetate concentration on apparent mobilities of analytes Conditions: Buffer:... 1.1 Sample preparation Analytical methods involve various processes such as sampling, sample preparation, separation, detection and data analysis Despite substantial technological advances in the analytical field, most instruments cannot handle complex sample matrices directly and, as a result, a sample preparation step is critical and takes up a major portion of analysis time The main aim of sample preparation. .. fabrication of 9 advanced materials coupled with good understanding of their behavior would be of paramount importance for the development of materials science as applied to analytical chemistry The essential part of SPBME lies in the extraction phase, which determines the extraction efficiency and thus the sensitivity and precision of the analysis The development of SPBME is closely related to that of materials... 5-1 Regression data and LODs of analytes combining FAEP and SBME Table 6-1 Regression data and LODs of analytes by ion-pair-LLLME Table 6-2 Regression data and LODs of analytes by EMI xii LIST OF FIGURES Figure 2-1 TG and DTA curves of the zirconia-coated PHF predried at 393 K Figure 2-2 Photographs of ZHF (a) and PHF (b) The scale shown is in cm Figure 2-3 XRD spectrum of ZHF m: monoclinic; t: tetragonal... 5-2 Effect of composition of organic solvents on apparent mobilities of analytes Conditions: buffer: 1 M acetic acid-25 mM ammonium acetate, different percentages of acetonitrile in methanol; Separation voltage: -30 kV Figure 5-3 An electropherogram of acidic herbicides Conditions: Buffer: 25 mM ammonium acetate -1 M acetic acid in methanol; Separation voltage: -30 kV; Sample: 20 µg/mL; Sample injection:... Figure 6-3 Influence of the concentration of TrBA on the extraction efficiency Extraction conditions: 0.5 µg/mL of the analytes in 4 mL solution at pH of 4, with different TrBA concentrations, 200 µL 1-octanol as transferring phase, 2 µL water as acceptor phase, 62.8 rad s-1,45 min Figure 6-4 Influence of the pH value of the donor phase on the extraction efficiency Concentration of TrBA: 0.1 mM TrBA... Figure 6-8 Electropherogram of an extract of river water which had been spiked with 0.1 µg/mL of the analytes Peaks: 1 MPA; 2 EMPA; 3 IMPA; 4 CMPA Figure 6-9 Influence of voltage on EMI Extraction conditions: sample solution: 0.5 µg /mL, 20 µL H2O as the acceptor phase, 62.8 rad s-1, 10 min, different voltages Figure 6-9 Influence of stirring speed on EMI Extraction conditions: sample solution: 0.1 µg... employed to further enhance the sensitivity of this method LODs, as low as ng/mL levels were achieved xi LIST OF TABLES Table 2-1 Pore structure parameters based on measurement of nitrogen adsorption /desorption Table 3-1 Optimization of synthetic conditions Table 4-1 Regression data and LODs of analytes Table 4-2 Level of PAHs (µg/g) in Singapore coastal sediment samples extracted with MAE-µ-SPE using... nitrogen adsorption/desorption isotherms of the hybrid monolith; Inset: Pore size distribution calculated from the desorption branch of the isotherm Ps: sample pressure; Po: saturation pressure Figure 3-6 (a) Electropherogram of water sample spiked with 500 µg/L anaesthetics after extraction by the hybrid silica monolith; (b) Electropherogram of human urine sample spiked with 500 µg/L anaesthestics . DEVELOPMENT OF MINIATURIZED SAMPLE PREPARATION APPROACHES XU LI NATIONAL UNIVERSITY OF SINGAPORE 2009 DEVELOPMENT OF MINIATURIZED SAMPLE PREPARATION. SEM of a single graphite fiber. xiv Figure 4-2 Influence of heating temperature on MAE efficiency. Figure 4-3 Time profile of MAE of PAHs. Figure 4-4 Time profile of elution of PAHs images of ZHF and PHF: (a) cross-sectional image of ZHF; (b) longitudinal image of ZHF; (c) textural image of ZHF; (d) textural image of PHF; (e) nanopores of ZHF; (f) fibrous structure of PHF.