Development and application of Sample Preparation Techniques for the Determination of Trace Organic Contaminants in Environment and food

Abstract

This thesis aimed to develop and apply sample preparation techniques for the determination of trace organic contaminants in environment and food. Two parts based on extraction phase were performed, including sorbent-based extraction and liquid phase-microextraction. In the first part focused on the development of solid-phase extraction (SPE) and magnetic solid-phase extraction (MSPE) for sorbent-based extraction techniques. Five sub-projects were carried out. The first sub-project was a metal organic frameworks material of MIL-101. It was successfully synthesized and utilized as a SPE adsorbent for the extraction and preconcentration of UV filters followed by gas chromatography-tandem mass spectrometry (GC-MS/MS). The high porous of MIL-101 adsorbent has large surface area and strong adsorption ability of UV filters through - and hydrophobic interactions. Under the optimum conditions, the developed method provided the linear in the range of 0.5 - 100 μg L1 with the low limits of detection in the range of 1.0 -11.7 ng L1. This method has been successfully applied for the extraction and quantification of UV filters in environmental and recreational water samples. The developed MIL-101 adsorbent provided good recoveries in a range of 82 - 105% with a relative standard deviations (%RSDs) in the range of 0.9 -9.7%. The second sub-project was polyaniline coated cigarette filters which were successfully synthesized and employed as the SPE adsorbent for the extraction and enrichment of polycyclic aromatic hydrocarbons (PAHs) in environmental water samples and quantified by high-performance liquid chromatography with fluorescence detector (HPLC-FLD). The high porosity and large surface area of cigarette filters helped to reduce the back pressure allowing extraction process at the high sample flow rate without loss of extraction ability. The coating of polyaniline facilitated the strong adsorption of PAHs via л-л interaction. Under the optimum conditions, the linearity was in the range of 0.005-10 μg L-1 with a low detection limit of 0.5 ng L1. This method provided a high enrichment factor and good recoveries in the range of 85 - 98% with RSDS in the range of 3.5 8.8%. The developed adsorbent is easy to prepare, cost-effective, environmentally friendly, reproducible and could be reused up to 18 times. The third sub-project was a hybrid adsorbent of calix[4]arene functionalized graphene oxide onto polydopamine-coated cigarette filters. This adsorbent was applied for the SPE and clean-up aflatoxins in corn samples followed by HPLC-FLD. This porous adsorbent included the combination of polydopamine, graphene oxide and calix[4]arene for the fabrication of a hybrid adsorbent which facilitated the highly efficient adsorption of aflatoxins via hydrogen bonding, hydrophobic and л- interactions. Under the optimum conditions, the developed adsorbent provided a linear response in the range of 0.01 - 10 ug kg1 with a detection limit of 0.01 μg kg1 for aflatoxin B1, 0.02-10 ug kg1 with a detection limit of 0.02 ug kg1 for aflatoxin B2 and 0.05 - 10 μg kg1 with a detection limit of 0.05 μg kg for aflatoxin G1 and aflatoxin G2. This method was successfully applied for the determination of aflatoxins from corn samples with satisfactory recoveries from 83 to 107% with the RSDs ranging from 0.20 to 14.7%. The developed adsorbent is simple to prepare, low cost and could be reused up to 17 times. The fourth and fifth sub-project were polyaniline and polypyrrole coated magnetite nanoparticles incorporated in alginate beads. The magnetic adsorbents were successfully synthesized and used as MSPE adsorbent for the extraction and preconcentration of PAHs and endocrine- disrupting compounds (EDCs) including estriol, ẞ-estradiol and bisphenol A in water samples followed by HPLC-FLD. The magnetite nanoparticles provided a simple and fast separation of the adsorbent from the sample solution using an external magnet. An alginate hydrogel helped to entrap the magnetite nanoparticles for increasing of dispersibility and enhancing the surface area for coating. The large surface areas of polyaniline coated alginate/magnetite composite helped to increase the extraction yield of PAHs via л-л interaction and polypyrrole coating facilitated the high adsorption of EDCs through hydrogen bonding, л-л and hydrophobic interactions. The developed method provided a wide linear range from 0.040 to 50 μg L1 with a low detection limit of 0.010 ug L1 for PAHs and from 0.50 to 100 μg L-1 with a low detection limit of 0.50 μg L-1 for EDCs. The developed adsorbent of polyaniline coated magnetite nanoparticles entrapped in alginate beads were applied for the extraction and preconcentration of PAHs in environmental water samples with a good recovery of 86 - 98% and the RSDs in the range of 3.1-8.3%. The developed adsorbent of polypyrrole coated magnetite nanoparticles entrapped in alginate beads were effectively applied for the extraction and determination of EDCs in environmental water samples with a good recovery of 91 - 98% and the RSD in the range of 3.0 - 7.2%. The developed adsorbents are simple to prepare, convenient, cost-effective, good reproducibility and environmentally friendly. In the second part focused on the development of liquid phase- microextraction approach called plunger-in-needle liquid phase-microextraction (PIN- LPME). The last sub-project was environmentally friendly method of etching a stainless steel plunger wire using ferric chloride-hydrochloric acid (FeCl3-HCI) solution as the etchant, replacing the conventional hydrofluoric acid use. The etching procedure was operated in one-step by immersing a stainless steel plunger wire directly into the etchant. The etched plunger wire provided rough surface, allowing stable organic solvent holder for PIN-LPME and then directly expose into water samples for the extraction of PAHs. The extract was subsequently subjected to thermal desorption in injector port of gas chromatograph for analysis. Under the optimal conditions, the developed method provided good linearity in the range of 0.01-50 μg L-', low detection limits in the range of 0.006-0.058 μg L-' and good reproducibility with RSDS in the range of 4.2 - 12.7%. The environmentally friendly etching method is simple, fast and one-step approach and successfully applied for extraction and enrichment of PAHs in water samples with good recovery of 84 - 102% and RSDs in the range of 1.0-9.5%. In conclusion, the sample preparation techniques were successfully developed and applied for the determination of trace organic contaminants in environment and food. These developed methods provided good analytical performance with several advantages, including simple to prepare, convenient, cost- effective and environmentally friendly. The developed methods have the potential to apply for the extraction and determination of others trace organic contaminant in environment and food samples coupled with chromatography for analysis.