DEVELOPMENT AND APPLICATION OF LIQUID-PHASE MICROEXTRACTION TECHNIQUES IN THE ANALYSIS OF ENVIRONMENTAL POLLUTANTS by HOU LI (M.Sc.) A thesis submitted for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry National University of Singapore 2003 Acknowledgments I would like to express my deepest gratitude to my supervisor Professor Lee Hian Kee, for his invaluable guidance, encouragement and concern throughout the entire project. Special thanks go to Mdm Frances Lim for her technical assistance and help. I would like to thank all of the research students in our laboratory, in particular Ms Zhu Lingyan, Ms He Yi, Mr Gong Yinhan, Mr Tu Chuanhong, Ms Wen Xiujuan, Ms Zhao Limian, Ms Sun Lei, Mr Zhu Liang, Mr Shen Gang, Mr Zhu Xuerong and Mr Chanbasha Basheer for their assistance and friendship. The financial assistance provided by the National University of Singapore during my Ph.D. candidature is also greatly appreciated. Finally, my deepest gratitude goes to my family for their unquestioning support, understanding and encouragement. i Summary As an active research field in analytical chemistry, sample preparation techniques is a key step in an analytical procedure and It has received increasing attention in the past decade. Recently, with the trend of miniaturization and automation, microscale sample preparation methods have begun to generate strong interest and have undergone rapid development. These procedures are environmentally friendlier, faster and easier to handle than conventional methods. Normally, microscale sample preparation techniques include sorbent-based and solvent-based microextraction. Sorbent-based microextraction is usually termed solid phase microextraction (SPME). Solvent-based microextraction which is also termed liquid-phase microextraction (LPME) features the use of microlitres of organic solvent for the extraction and enrichment of analytes. This work focuses on the development and application of two kinds of liquidphase microextraction techniques. One is drop-based solvent microextraction including static liquid-phase microextraction (extraction solvent drop remains static during extraction) and dynamic liquid-phase microextraction (extraction solvent plug is agitated during extraction). Non-polar or lower polarity analytes such as polycyclic aromatic hydrocarbons can be detected by both of the two modes combined with HPLC. The parameters influential to extraction were investigated, and the applicability of the methods to environmental water was also evaluated. Another microextraction approach involves the use of hollow fiber combination with liquid-phase microextraction. It can be categorized into two- ii phase microextraction, and three-phase microextraction or liquid-liquid-liquid microextraction (LLLME). By using hollow fiber membrane, the organic solvent is held and protected by the membrane during the extraction process. Hence the precision and stability of the methods are increased significantly. Also, sample clean-up is possible by using this method because of the selectivity of the hollow fiber so that it can be applied to “dirty” samples such as soil slurries and biological fluids, etc. Hollow fiber protected dynamic two phase microextraction has been developed and evaluated for the analysis of pesticides. Trace amounts of pesticides have been determined from both water and soil, after extraction using this procedure, by gas chromatography-mass spectrometry. Three-phase hollow fiber microextraction is suitable for the extraction of polar and ionizable analytes such as beta-blockers (drugs) and anilines (environmental pollutants) etc. Static three-phase microextraction combined with on-line stacking has been developed to extract and enrich several drugs prior to CE analysis. A novel approach, named dynamic three-phase microextraction, has also been developed and evaluated by using aniline compounds as the model analytes. In comparison of dynamic three-phase microextraction with static three-phase microextraction, the former provided higher extraction efficiency in a shorter time. The results presented in this thesis show that all the liquid-phase microextraction techniques can serve as excellent alternative methods to conventional sample preparation techniques in the analysis of organic pollutants or drugs in aqueous samples. iii List of abbreviations SPME solid-phase microextraction LPME liquid-phase microextraction LPME/HF liquid-phase microextraction with hollow fiber LLLME liquid-liquid-liquid microextraction LLE liquid-liquid extraction SPE solid-phase extraction SME solvent microextraction USEPA United States Environmental Protection Agency SFE supercritical fluid extraction VOCs volatile organic compounds LC liquid chromatography GC gas chromatography FIE flow injection extraction CFME continuous flow microextraction PDMS polydimethylsiloxane PA polyacrylate PAHs polycyclic aromatic hydrocarbons GC/MS gas chromatography/mass spectrometry LC/MS liquid chromatography/ mass spectrometry ECD electron capture detection iv CE capillary electrophoresis UV ultra violet PEEK polyetheretherketone SME/BE solvent microextraction with simultaneous back extraction LPME/BE liquid-phase microextraction with simultaneous back extraction HF hollow fiber RSD relative standard deviation BLM bulk liquid membrane SLM supported liquid membrane IS internal standard LOD limit of detection OCPs organochlorine pesticides TCB trichlorobenzene EF enrichment factor SIM selection ion monitoring OF organic film ASP aqueous sample plug OP organic phase 3-NA 3-nitroaniline 4-CA 4-chloroaniline 4-BA 4-bromoaniline 3,4-CA 3,4-dichloroaniline PCBs polychlorinated biphenyls v BSA bovine serum albumin BTEX benzene, toluene, ethylbenzene and o-xylene OCPs organochlorine pesticides ppm parts per million ppb parts per billion ppt parts per trillion CITP capillary isotachophoresis CGE capillary gel electrophoresis CIEF capillary isoelectrophoretic focusing CZE capillary zone electrophoresis MEKC micellar electrokinetic chromatography EOF electroosmotic flow CEC capillary electrochromatography vi Contents Chapter Preface 1.1 Introduction .1 1.2 Sample preparation techniques 1.3 Sorbent-based microextraction .7 1.4 Solvent-based microextraction .9 1.4.1 Flow injection extraction (FIE) .10 1.4.2 Drop-based liquid-phase microextraction 11 1.4.2.1 LPME .11 1.4.2.2 LPME with simultaneous back-extraction .18 1.4.2.3 Theory of LPME .21 1.4.3 Hollow fiber-protected LPME .21 1.4.3.1 Two-phase hollow fiber-protected LPME 22 1.4.3.2 Three-phase hollow fiber-protected LPME .23 1.4.3.3 Theory of three-phase hollow fiber-protected LPME 27 1.5 Scope of study 28 Chapter Drop-based liquid-phase micro-extraction technique combined with HPLC analysis 30 2.1 Introduction .30 2.1.1 HPLC .30 2.1.2 Drop-based LPME .31 2.1.3 Polycyclic aromatic hydrocarbons (PAHs) .32 2.2 Experimental .33 2.2.1 Chemicals and samples 33 2.2.2 Silanization of glassware .34 2.2.3 Drop-based LPME procedures 35 2.2.3.1 Extraction of PAHs by static LPME 35 2.2.3.2 Extraction of PAHs by dynamic LPME .36 2.2.4 Apparatus 38 2.3 Results and discussion .38 2.3.1 Static LPME for trace analysis of PAHs in river water .38 2.3.1.1 Selection of extraction solvent 39 2.3.1.2 Selection of organic drop size 40 2.3.1.3 Speed of agitation 41 2.3.1.4 Selection of extraction time 43 2.3.1.5 Linearity, reproducibility and sensitivity 45 2.3.1.6 Extraction of PAHs in river water and tap water by static LPME…………………… .47 2.3.2 Dynamic LPME in trace analysis of PAHs in drain water .49 2.3.2.1 Selection of extraction solvent 49 2.3.2.2 The volume of extraction solvent 50 2.3.2.3 Syringe plunger movement 51 2.3.2.4 Sampling volume 53 vii 2.3.2.5 Effect of salt on the extraction 54 2.3.2.6 Temperature .55 2.3.2.7 Linearity, reproducibility and sensitivity 57 2.3.2.8 Extraction of PAHs in drain water and tap water by dynamic LPME …………………………………………………………………… .57 2.4 Conclusions and future research 60 Chapter Two-phase hollow fiber-protected liquid-phase microextraction technique combined with GC/MS 61 3.1 Introduction .61 3.1.1 Gas chromatography 61 3.1.2 Pesticides in aqueous samples .63 3.1.3 Extration of soil sample .65 3.2 Theory 66 3.2.1 Automated two-phase hollow fiber-protected dynamic LPME .66 3.2.2 Solid-phase microextraction 67 3.3 Experimental .68 3.3.1 Standards and reagents 68 3.3.2 Soil sample preparation .71 3.3.3 GC/MS analysis .71 3.3.4 Apparatus 73 3.3.5 Extraction procedures 74 3.3.5.1 Two-phase hollow fiber-protected dynamic LPME .74 3.3.5.2 Solid-phase microextraction .75 3.4 Results and discussion .76 3.4.1 Determination of pesticides in pond water and slurry sample by twophase hollow fiber-protected LPME .76 3.4.1.1 Selection of the organic solvent 76 3.4.1.2 Selection of the number of samplings (extraction cycles) .77 3.4.1.3 Selection of the movement pattern of plunger 78 3.4.1.4 Selection of the speed of agitation .82 3.4.1.5 Method evaluation 83 3.4.1.6 Analysis of pesticides in pond water and slurry samples 86 3.4.2 Determination of pesticides in soil by two-phase hollow fiberprotected LPME and GC/MS .87 3.4.2.1 Selection of extraction solvent 87 3.4.2.2 Effect of extraction time 88 3.4.2.3 Effect of the movement pattern of the plunger on the extraction 90 3.4.2.4 Effect of the organic solvent content in aqueous soil samples on LPME efficiency 91 3.4.2.5 Effect of humic acid concentration on LPME efficiency 92 3.4.2.6 Effect of salt concentration on LPME efficiency 93 3.4.2.7 Method evaluation 94 3.4.2.8 Extraction from aged soil sample .97 3.5 Conclusions and future research 99 viii Chapter Three-phase liquid-phase micro-extraction technique combined with capillary electrophoresis .100 4.1 Introduction .100 4.1.1 General remarks of capillary electrophoresis 100 4.1.2 Basic principles of CE 101 4.1.3 Different modes of CE .102 4.1.4 Application of CE to the analysis of drugs and pollutants 103 4.1.5 Off-line and on-line concentration techniques for capillary electrophoresis 103 4.1.6 Scope of project .105 4.1.6.1 Static three-phase LPME for aminoalcohols 106 4.1.6.2 Dynamic three-phase LPME .107 4.2 Experimental .108 4.2.1 Equipment .108 4.2.2 Chemicals and solvents .109 4.2.3 Materials 111 4.2.4 Extraction setup and procedures .111 4.3 Results and discussion .114 4.3.1 Preconcentration of aminoalcohols in urine by combined use of offcolumn static three-phase LPME and on-column stacking for trace analysis by CZE ………………………………………………………………………….114 4.3.1.1 Determination of aminoalcohols by CZE with off-column static three-phase LPME .114 4.3.1.2 Determination of aminoalcohols by CZE with field-amplified concentration 115 4.3.1.3 Determination of aminoalcohols by CZE with LPME-CE/FAC 117 4.3.1.4 Quantitative analysis 120 4.3.1.5 Human urine sample analysis 121 4.3.2 Preconcentration of anilines by dynamic three- phase LPME for trace analysis by CZE 124 4.3.2.1 Mass transfer model .124 4.3.2.2 Basic principles 126 4.3.2.3 Optimization of dynamic three-phase LPME 128 4.3.2.4 Evaluation of dynamic three-phase LPME .135 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Lee, Combination of liquid phase microextraction and on-column stacking for trace analysis aminoalcohols by capillary electrophoresis, J. Chromatogr. A of 2002 (979) 163-169. 3. L. Hou, G. Shen, H.K. Lee, Automated hollow fiber-protected dynamic liquid phase microextraction of pesticides with GC/MS analysis, J. Chromatogr. A 2003 (985) 107-116. 4. L. Hou, H.K. Lee, Dynamic three phase microextraction as a sample preparation technique prior to capillary electrophoresis Anal. Chem. 2003 (75) 2784-2789. 5. L. Hou, H.K. Lee, Determination of pesticides in soil sample by liquidphase microextraction and gas chromatography/mass spectrometry, submitted to J. Chromatogr. A (submitted) Conference papers 6. L. Hou, X.J. Wen, H.K. Lee, Liquid phase microextraction of basic drugs with analysis by capillary electrophoresis, Symposium on Challenges in Novel Separation and Purification, 29-30 October 2001, Singapore. 155 7. L. Hou, H.K. Lee, Solvent microextraction of pesticides in soil with analysis by GC-MS, 2nd Singapore International Chemical Conference, 18-20 December 2001, Singapore. 8. L. Hou, H.K. Lee, Semi-automation of dynamic liquid-phase microextraction in determination of polycyclic aromatic hydrocarbon, 7th International Symposium on Hyphenated Techniques in Chromatography and Hyphenated Chromatographic Analyzers, 6-8 February 2002, Belgium. 9. L. Hou, H.K. Lee, Application of LPME/HPLC method for polycyclic aromatic hydrocarbons Hyphenated analysis, Techniques in 7th International Chromatography Symposium and on Hyphenated Chromatographic Analyzers, 6-8 February 2002, Belgium. 10. L. Hou, H.K. Lee, Automated dynamic liquid phase microextraction using hollow fiber prior to GC-MS analysis, 7th International Symposium on Hyphenated Techniques in Chromatography and Hyphenated Chromatographic Analyzers, 6-8 February 2002, Belgium. 11. L. Hou, X.J. Wen, C.H. Tu, H.K. Lee, Combination of liquid phase microextraction and on-column stacking for trace analysis of aminoalcohols by capillary electrophoresis, 15th International Symposium on Microscale Separations and Analysis, 13-18 April 2002, Sweden. 12. L. Hou, G. Shen, H.K. Lee, Determination of pesticides by hollow fiberprotected dynamic solvent microextraction, 25th International Symposium on Chromatography, 13-17 May 2002, Italy. 156 13. L. Hou, H.K. Lee, Determination of pesticides in soil sample by liquidphase microextraction, 24th International Symposium on Capillary Chromatography, 15-20 September 2002, Germany. 157 [...]... aqueous phase of the outer drop contained the analyte of interest and was continuously delivered and aspirated away throughout the sampling The analytical response of the instrument was linearly 11 related to the analyte concentration and precision (5.0%) was assumed to be affected by the organic drop volume variation during the determination process While the kinetics of the process were not described in. .. most of the phenols within 35 min Application of this 19 method to the analysis of aromatic amines combined with HPLC was also reported [68] Further development of this LPME /BE technique was achieved by enlarging the volume ratio of donor phase to receiving phase since the higher volume ratio could lead to much higher enrichment factor [69] The authors reduced the volume of the aqueous receiving phase. .. by the extracting phase for in- tube SPME So far, on-fiber SPME is the most popular one in the field of microextraction methodology [2331] Generally, on-fiber SPME is combined with GC analysis and also can be accommodated in a modified HPLC injector for analysis In spite of the popularity of on-fiber SPME, in- tube SPME is another important concept because it offers a range of extracting phases and the. .. plunger Secondly, the repeated aspiration of the ASP, following the first sampling cycle, ensures that both the OF and the ASP are periodically renewed, and thus the OF would be in contact with fresh aqueous sample having the initial analyte concentration in the sample vial Later, the same research group applied static mode of LPME to the analysis of eight organochlorine pesticides in water [49] Factors... extended the above drop-based technique to extract free progesterone in a protein solution [48] In the presence of 1% (w/v) bovine serum albumin (BSA), the extraction rate of analyte was increased, thus the processes of diffusion, adsorption and desorption of analyte to the protein film formed at the liquid- liquid interface were assumed to enhance mass transfer of analyte He and Lee introduced the term liquid- phase. .. a GC instrument for further analysis Essential information regarding equilibrium and kinetics of the process was also given The mass transfer coefficient was tentatively interpreted in overall terms of the film theory However, one drawback of both drop -in- drop system and the single-drop microextraction system is that extraction and injection was performed separately in two different devices For the. .. relevant to the extraction process were investigated The sensitivity of the method was enhanced with agitation, and increasing the extraction temperature, of the sample solution On the other hand, the dynamic LPME work was extended to the analysis of ten chlorobenzenes with GC analysis [50] The role of some important factors that influence the extraction efficiency was determined Good linearity, sensitivity,... a matter of increasing interest to the water industry, scientists and the general public alike, from the point of view of possible health hazards presented to both human and animal life It has been estimated that new chemicals, most of which are organic, are invented and brought into use at a rate of over 1000 per year [2] Many of these will find their way into the aqueous environment as industrial... effects and long-term instability because of the use of a new hollow fiber of every extraction Figure 1-6 Diagram of the three -phase LPME extraction unit (not to scale) The above work was employed to the analysis of acidic drugs present in water sample and in human urine [82] The acid drugs, ibuprofen, naproxen, and ketoprofen were extracted from the acidified sample solutions into dihexyl ether phase. .. µl) into a GC system to increase the amount of sample and therefore method sensitivity [36, 37] There is a similar solvent microextraction method in EPA standard methodologies [8] to analyze organochlorine pesticides and commercial polychlorinated biphenyl (PCBs) in water In the 1980s [38, 39], the main development of solvent microextraction was flow injection extraction (FIE) FIE has the advantages of . DEVELOPMENT AND APPLICATION OF LIQUID- PHASE MICROEXTRACTION TECHNIQUES IN THE ANALYSIS OF ENVIRONMENTAL POLLUTANTS by HOU LI (M.Sc.) A thesis submitted. approach involves the use of hollow fiber combination with liquid- phase microextraction. It can be categorized into two- iii phase microextraction, and three -phase microextraction or liquid- liquid -liquid. 4.1.2 Basic principles of CE 101 4.1.3 Different modes of CE 102 4.1.4 Application of CE to the analysis of drugs and pollutants 103 4.1.5 Off-line and on-line concentration techniques for