MEMBRANE PROTECTED MICRO-SOLID PHASE EXTRACTION OF PHARMACEUTICALS FROM ENVIRONMENTAL WATER SAMPLES LIM TZE HAN (BSc (Hons), MSc, NUS) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY NUS GRADUATE SCHOOL FOR INTEGRATIVE SCIENCES AND ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2013 Declaration I hereby declare that the thesis is my original work and it has been written by me in its entirety. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has not been submitted for any degree in any university previously. LIM Tze Han 15th June 2013 ! ACKNOWLEDGEMENTS Heartfelt thanks is extended to my supervisors; Prof LEE Hian Kee and Dr HE Chaobin, and members of my thesis advisory committee; Prof Li Fong Yau, Sam and Dr Li Jun for the patience, support and advice offered during my candidature. Special thanks to Dr Liu Qiping for her patience in instruction and assistance in the chromatography laboratory (Department of Chemistry, NUS) I am most grateful for the offer of a research scholarship by the NUS Graduate School for Integrative Sciences and Engineering (NGS) and the generous support extended by NGS and her staff members during my candidature. ! TABLE OF CONTENTS List of Abbreviations/symbols I List of Tables III List of Figures IV Summary CHAPTER INTRODUCTION 1.1 Preface 1.2 Conventional methods of preparing environmental water samples for PAI analysis 1.3 Membrane-protected microextraction 10 1.4 μ-SPE in perspective 11 1.5 Sorbent selection in μ-SPE: Literature review 16 1.6 Thesis scope and objective 19 References 21 CHAPTER METHODOLOGY 25 2.1 Preface 26 2.2 Preparation of sorbents 31 2.3 Characterization of sorbents 37 2.3.1 Elemental analyses 37 2.3.2 TGA 37 2.3.3 EWC 38 Evaluation of μ-SPE performance (EF and Rr) 39 2.4.1 Evaluation of EF 39 2.4.2 Evaluation of Rr 40 References 40 2.4 CHAPTER 3.1 3.2 EXPERIMENTAL 42 Chemicals and materials 43 3.1.1 Analyte standards 43 3.1.2 Solvents and pH modifiers for chromatography 43 3.1.3 Membranes 43 3.1.4 Sorbents and reagents for their surface modification 44 Method development 44 3.3 3.2.1 Preparation of spiked water samples 44 3.2.2 Preparation of spiked environmental water samples 45 3.2.3 μ-SPE 45 3.2.4 Liquid chromatography (LC) 46 μ-SPE devices 46 3.3.1 Device preparation 46 3.3.2 Preparation of surface modified sorbents 47 3.3.2.1 Preparation of APS 47 3.3.2.2 Preparation of UPS 47 3.3.2.3 Preparation of ZIPS 47 3.3.3 Characterization of sorbents and sorbent-containing devices 48 3.3.3.1 N,S elemental analyses 48 3.3.3.2 TGA 48 3.3.3.3 Determination of EWC 48 References 49 RESULTS AND DISCUSSION 50 Preparation of sorbents 51 4.1.1 Preparation of APS and UPS 51 4.1.2 Preparation of ZIPS 53 4.2 EWC 54 4.3 Comparison of sorbents 55 4.4 Suggested sorption of extracted analytes by UPS and ZIPS 57 4.5 Optimization studies for UPS-based μ-SPE 58 4.5.1 Sample pH 58 4.5.2 Desorption time 59 4.5.3 Volume of desorption solvent 60 4.5.4 Optimal EF and comparison with previously reported EF values 61 Optimization studies for UPS-based μ-SPE 63 4.6.1 Sample pH 63 4.6.2 Desorption time 64 4.6.3 Volume of desorption solvent 65 CHAPTER 4.1 4.6 4.6.4 Optimized EF and comparison with previously reported EF values 65 Method performance 67 4.7.1 Limits of detection (LOD) and quantification (LOQ) 67 4.7.2 Relative recovery 70 References 70 CHAPTER CONCLUDING REMARKS 72 CHAPTER SUGGESTIONS FOR FUTURE WORK 74 References 76 Publications 77 4.7 ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! APPENDIX LIST OF ABBREVIATIONS/SYMBOLS Ami Amitriptyline hydrochloride AMP Analytical measurement process APS 1-aminopropyl grafted silica gel sorbents APTES 3-aminopropyltriethoxysilane coupling reagent C18-silica gel Commercial n-octadecyl modified silica gel Cbz Carbamazepine CE Capillary electrophoresis Dfn Diclofenac DVB Divinylbenzene EF Enrichment factor EWC Equilibrium water content HF-LPME Hollow fiber assisted liquid phase microextraction HILIC Hydrophilic interaction liquid chromatography HLB Hydrophilic-lipophilic balance LC Liquid chromatography LLE Liquid-liquid extraction LOD Limit of detection LOQ Limit of quantification muSPE Micro solid phase extraction using mixed matrix membrane μ-SPE Membrane bag micro solid phase extraction MPME Membrane protected microextraction MWCNT Multi-walled carbon nanotube NVP N-vinylpyrrolidone OCP Organochlorine pesticide OPP Organophosphate pesticide OPM Oligomeric and polymeric materials PAH Polyaromatic hydrocarbon PAI Pharmaceutically active ingredient PBDE Polybrominated diphenyl ether PCB Polychlorinated biphenyl POCIS Polar organic chemical integrative sampler ! I! PS 1,3-Propane sultone Rr Relative recovery RSD Relative standard deviation SBME Solid bar microextraction SPE Solid phase extraction SPME Solid phase microextraction TEA Triethylamine TGA Thermogravimetric analysis UPS Ureido grafted silica gel sorbents ZIPS Zwitterion grafted silica gel sorbents ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! II! LIST OF TABLES ! Table No. Caption 4-1 Comparison of EF data for UPS-based μ-SPE with SPME, and previously reported static mode membrane microextraction methods 4-2 Comparison of EF data for ZIPS-based μ-SPE with SPME, and previously reported static mode membrane microextraction methods 4-3 Method performance for UPS-based μ-SPE 4-4 Method performance for ZIPS-based μ-SPE ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! III! LIST OF FIGURES CHAPTER INTRODUCTION Fig No. Caption 1-1 Widely reported organic pollutants in the freshwater environment 1-2 Work-flow in typical sample preparation and its palcement in an analytical measurement process 1-3 Molecular structures of divinylbenzene isomers (I and II) and N-vinylpyrrolidone monomers (III) 1-4 Illustration of conventional membrane filtration modes 1-5 Schematic illustration of (a) dead-end filtration and (b) crossflow filtration 1-6 Illustration of a POCIS device 1-7 Loose, powdered sorbents enclosed within membrane pouches as μ-SPE devices 1-8 Proposed schematic of a typical μ-SPE process 1-9 Pre-concentration of analytes during μ-SPE 1-10 μ-SPE of ketoprofen and ibuprofen with commercially available sorbents as reported by Basheer et al CHAPTER Fig No. Caption 2-1 Chemical structures of investigated analytes 2-2 Surface modified silica gel employed in this work 2-3 Illustration of the repellent properties of zwitterated silica surfaces towards protein (P) sorption 2-4 Preparation of APS sorbents through reaction between silica gel and 3-aminopropyltriethoxysilane coupling reagent 2-5 Proposed schematic of UPS preparation 2-6 Grafting from reaction strategy for preparing ZIPS CHAPTER ! Fig No. Caption 4-1 Thermogravimetric analysis of silica gel (Sil) and surface modified silica gel sorbents: ODS, APS and UPS 4-2 Comparison of EWC for ZIPS, UPS, APS and ODS for μ-SPE of Ami, Cbz, Ket and Dfn 4-3 EF for Ami, Cbz, Dfn and Ket during μ-SPE from their aqueous solutions using surface modified silica gel sorbents IV! Chapter 4. Results and Discussion Table 4-1 Comparison of EF data for UPS-based μ-SPE with SPME, and previously reported static mode membrane microextraction methods Analyte Calculated EF Reported Microextraction (UPS μ-SPE) EF methods 313 3-phase HF-LPME [19] 265.9 Conventional SPME [20] 44 Solid bar microextraction [21] 39 2-phase HF-LPME [22] 84 2-phase HF-LPME [22] 96 3-phase HF-LPME [22] 32 Electromembrane extraction [23] 55 Solid bar microextraction [21] 49 Electromembrane extraction [23] Ami 92 Cbz a 57 Ket 126 Dfn Ref. 71 a μ-SPE conditions: extraction time 60 min, desorption time of with methanol as desorption solvent, pH adjusted to 1.69, sample volume 50 mL, stirring speed 700 rpm b Hollow-Fiber-Liquid Phase Microextraction c Solid Phase Microextraction 62# Chapter 4. Results and Discussion 4.6 OPTIMIZATION STUDIES FOR ZIPS-BASED μ-SPE 4.6.1 SAMPLE PH Comparable and relatively constant EF values were observed for all analytes during extraction at acidic pH values (Fig 4-7). Fig 4-7. Effect of pH on analyte EF during μ-SPE using ZIPS sorbents. μ-SPE conditions: extraction time 60 min, desorption time of with methanol (200 μL) as desorption solvent, sample volume 50 mL, stirring speed 700 rpm. EF values for Cbz remained constant even as pH was increased into the alkaline region and possibly indicated that ionization of Cbz did not occur in the pH range studied. A sharp decrease in EFs occurred for Ket and Dfn above pH indicating that ionized forms of the analytes are not well extracted by ZIPS, possibly due to repulsion between the negatively charged carboxylate salts of Ket and Dfn, and the corona of sulfonate motifs on ZIPS surfaces. EFs for Ami increased only slightly as pH was increased beyond and indicated that the sorption of Ami and its de-protonated form onto ZIPS surfaces did not 63# Chapter 4. Results and Discussion differ significantly. As such, optimal EF for the selected analytes, can still be determined at the preferred pH of 1.69 ([...]... SUMMARY Membrane- assisted micro- solid phase extraction (μ-SPE) is a recently introduced sample preparation technique that integrates microextraction paradigms and membrane microfiltration with solid phase extraction It involved no more than a two-step workflow and enabled concurrent analyte extraction, sample clean up and enrichment It is well suited for analyses of environmental water samples μ-SPE of. .. analytical extraction procedures such as SPE and classical liquid liquid extraction (LLE) Microextraction techniques are characterized by the extraction of analytes from a given donor phase, into a minuscule volume of a selected acceptor phase This enabled concurrent occurrence of analyte extraction and pre-concentration [42] Incorporating a microfiltration membrane at the interface of both phases, enabled... and non-volatile compounds that in the absence of chemical derivatization, mandated analysis by liquid chromatography (LC) or capillary electrophoresis (CE) They are exemplified by the techniques of mixed matrix (hollow-fiber) membrane micro- solid phase extraction pioneered by Mitra’s group [50-60], and microporous membrane- protected micro solid phase extraction (μ-SPE) pioneered by Lee’s group [61-66,... sorbents for solid phase extractions of environmental water samples and may be explored further in future studies ' Chapter 1: Introduction CHAPTER 1: INTRODUCTION 1" Chapter 1: Introduction 1.1 PREFACE It is crucial that environmental freshwater sources such as lakes, rivers and groundwater be regularly monitored [1-3] for the presence of pollutants, because they are sources of drinking water in many... requiring samples to be constituted in solvents compatible with these analytical systems prior to actual analysis 1.2 CONVENTIONAL METHODS OF PREPARING ENVIRONMENTAL WATER SAMPLES FOR PAI ANALYSIS Solid phase extraction (SPE) using Oasis HLB® sorbents remains the conventional strategy of preparing environmental water samples for PAI analyses [1, 8, 11, 17, 18] as attested to by the number of related... technique of solid phase membrane- tip extraction where cone-shaped membrane cups containing selected sorbents were manually inserted, and physically immobilized into the end of a micropipette tip Extraction occurred following repeated uptake and release of sample solution into the micropipette tip and was amendable to semi-automation This technique was eventually used for the extraction of triazine... Reproduced with permission from [29] Membrane protected SPE disks in the form of Polar Organic Chemical Integrative Sampler (POCIS), whereby selected sorbents were sandwiched between polyethersulfone microfiltration membrane sheets (figure 1-6, Huckins et al [31, 32]), have been highly popular for passive sampling cum extraction of polar organic contaminants from environmental water sample 8" Chapter... triazine herbicides from environmental water samples using MWCNT sorbents 17" Chapter 1: Introduction In a separate report, Al-Hadithi et al [68] had several surface modified silica gel sorbents, individually and physically entrapped within the lumen of individual, microporous (average pore radii of 0.2μm) polypropylene hollow fiber membranes The resulting technique of solid bar microextraction (SBME)... to extractions of estrogens in ovarian cyst fluids [63] and aldehydes in rainwater [64] and are noteworthy for the demonstrated use of analyte (chemical) derivatization in-conjunction with μ-SPE The technique has even been employed for extractions of carbamates [65], and mixtures of organochlorine pesticides (OCP) and polychlorinated biphenyls (PCB) [66] from remains of semi -solid samples post microwaveassisted... concentration of a given analyte that can be successfully extracted from spiked water samples during μ-SPE, and transferred into an optimized volume of methanol for analysis by LC 15" Chapter 1: Introduction CW is the final concentration of the same analyte that can be successfully extracted using μ-SPE, and transferred into the same volume of methanol for LC analysis, but from environmental water samples . MEMBRANE PROTECTED MICRO- SOLID PHASE EXTRACTION OF PHARMACEUTICALS FROM ENVIRONMENTAL WATER SAMPLES LIM TZE HAN (BSc (Hons),. Membrane- assisted micro- solid phase extraction (μ-SPE) is a recently introduced sample preparation technique that integrates microextraction paradigms and membrane microfiltration with solid. METHODS OF PREPARING ENVIRONMENTAL WATER SAMPLES FOR PAI ANALYSIS Solid phase extraction (SPE) using Oasis HLB® sorbents remains the conventional strategy of preparing environmental water samples