Development of Porous Composite Adsorbents for the Extraction and Determination of Trace Organic Compounds in Foods and Personal Care Products

Abstract

This thesis aimed to develop porous composite adsorbents for the extraction, enrichment and determination of trace organic compounds in foods and personal care products before analysis with chromatographic technique. This thesis consists of three sub-projects divided by type of the adsorbent, extraction process and target analytes. In the first sub-project, the high porous monolith adsorbent of polypyrrole composite octadecyl silica and graphene oxide embedded in chitosan cryogel (PPY/C18/GOx/Chi) was successfully developed and utilized as SPE sorbent for the extraction of four carbamate pesticides including carbofuran, carbaryl, isoprocarb, and diethofencarb in fruit juices. The sponge-like structure of chitosan cryogel adsorbent not only can reduce back pressure in SPE cartridge but also can improve the adsorption site of the adsorbent that help to entrap other composite materials into the pore or its surface. The composite materials of polypyrrole, octadecyl and graphene oxide can adsorb carbamate pesticides via hydrophobic interaction, π-π interaction and hydrogen bonding. Under the optimum conditions of HPLC system and the extraction process, the porous composite monolith adsorbent exhibited wide linear responses from 2 to 500 µg L-1 for isoprocarb, 1 to 500 µg L-1 for diethofencarb and carbofuran and 0.5 to 500 µg L-1 for carbaryl. The limit of detections (LODs) were in the range of 0.5 to 2 µg L-1. The recovery of PPY/C18/GOx chitosan cryogel adsorbent when applied to extract four carbamate pesticides in apple, grape, orange, tomato and pomegranate juices were achieved from 84 to 99% with relative standard deviations (RSDs) lower than 6%. Moreover, it was great stability which can be reused up to 13 extraction cycles. For the second sub-project, the doubly porous composite of polyaniline, octadecyl-bonded silica magnetite nanoparticles and graphene oxide incorporated in alginate beads (PANI/C18@SiO2@Fe3O4/GOx) was fabricated and employed as magnetic solid phase extraction adsorbent (MSPE) for the extraction, enrichment and determination of fluoroquinolones. Polyaniline and graphene oxide can adsorb target fluoroquinolones via hydrogen bonding and π-π interaction and C18 can adsorb target fluoroquinolones via hydrophobic interaction. The double porous structure of alginate hydrogel was established by the reaction between calcium carbonate and hydrochloric acid. It can help to enhance the surface area for polyaniline coating which provided high adsorption site to adsorb fluoroquinolones. The magnetic nanoparticles in alginate beads promoted convenient and rapid separate the adsorbent from sample solution by applying only an external magnet. Under the optimal condition, the doubly porous alginate adsorbent provided low limit of detection from 0.001 to 0.01 µg L-1. The linearity of PANI/C18@SiO2@Fe3O4/GOx/Algi adsorbent were obtained in the range of 0.01 to 50 µg L-1 for difloxacin and sarafloxacin, 0.005 to 50 µg L-1 for ciprofloxacin, enrofloxacin and norfloxacin and 0.001 to 50 µg L-1 for danofloxacin. When the PANI/C18@SiO2@Fe3O4/GOx/Algi adsorbent was applied to extract and pretreat fluoroquinolones in eggs, honey and milk samples, the satisfactory recoveries were acquired from 81 to 98%. It also provided good reproducibility with the RSDs less than 9% and good reusability which can be used to extract the target fluoroquinolones up to 7 times. The third sub-project was the polydopamine coated porous composite materials of metal organic framework and Fe3O4 nanoparticles incorporated in carrageenan beads (PDA/MIL-101/Fe3O4/Carr) for the extraction of parabens. Carrageenan hydrogel was utilized as biodegradable and non-toxic supporting material which can easily entrap the composite materials and Fe3O4 nanoparticles. Metal organic frameworks type MIL-101(Cr) and polydopamine were used as the main composite materials to interact with four target parabens via hydrophobic interaction, hydrogen bonding and π-π interaction. Various affecting factors were investigated and optimized to obtain the best extraction efficiency. The results of PDA/MIL-101/Fe3O4/Carr adsorbent showed low limit of detections for all parabens from 0.05 to 1.0 µg L-1 and wide linear response in the range of 2 to 100 µg L-1 for butyl paraben and propyl paraben, 0.5 to 100 µg L-1 forethyl paraben and 0.1 to 100 µg L-1 for methyl paraben. The good recoveries of the PDA/MIL-101/Fe3O4/Carr beads for parabens extraction in mouthwash and skin cleansers were achieved between 80 to 96% with relative standard deviations lower than 7%. It also had good physical stability which can be used for the extraction of parabens up to 6 cycles. In the conclusion, the porous composite adsorbents were successfully fabricated and utilized for the extraction and enrichment of trace organic compounds in foods and personal care products before analysis with HPLC technique. These developed adsorbents exhibited high extraction efficiency, good reusability and reproducibility. There are several advantages including simple to prepare, convenient to use, environmentally and friendly. Moreover, the developed porous composite adsorbents can be applied for the extraction and determination of other organic compounds by modifying to achieve the suitable extraction condition with the target compounds.