Application Of Novel Liquid Phase Microextraction Methods In The Analysis Of Fungicides Residues

Sample preparation is an indispensable step in the analysis of organic contaminant residues in foodstuff and environmental samples. The purpose of sample preparation is to separate and concentrate the target analytes from the complex sample matrix, thus reducing or eliminating the interferences of impurity in the sample to achieve the determination of analytes at trace levels. However, with the continuous development of science and technology, people put forward higher requirements for the analytical accuracy. How to establish a simple, efficiency, rapid and environrmentally friendly sample preparation methodologies have attracted much attention.Recently, a novel sample preparation methodology called liquid phase microextraction (LPME) has been developed based on liquid phase extraction. The proposed method combined extraction, separation and concentration in one step. LPME can offer many advantages such as simplicity of operation, high extraction efficiency. In addition, LPME required less organic solvent, thus proving to be an environmentally friendly technique. These advantages make the LPME technology widely used in foodstuff, medicine, biology and environment, etc. In this thesis, three modes of LPME technology including vortex-assisted liquid-liquid microextraction (VALLME), magnetic stirring-assisted dispersive suspended microextraction, motor stirrer-assisted single drop microextraction were developed for the determination of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in environmental and foodstuff samples followed by high performance liquid chromatography (HPLC). The main contents and results are as followings:(1) A VALLME combined with HPLC was developed for sensitive determination of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in aqueous samples. This novel technique performed extraction, separation, preconcentration, and injection in one step using a5-mL syringe, thus expanding the level of automation on VALLME. Under the optimized conditions, the limits of detection and enrichment factors were0.96μg·L-1,144for azoxystrobin,1.33μg·L-1,183for diethofencarb, and0.73μg·L-1,176for pyrimethanil. The recoveries of the spiked real water samples (tap water, the south lake water, rain water) ranged from81.3-116.8%. The study highlighted the proposed technique as a simple, efficient, and easily operable approach for the determination of three fungicides in aqueous samples.(2) A simple method of magnetic stirring-assisted dispersive suspended microextraction with solidification of floating organic droplet was developed for the identification of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water and wine samples followed by HPLC. In the proposed method, both the extraction and phase separation process were performed with the help of magnetic stirring. During the extraction process, the magnetic stir bar continuously rotated at a high speed. The extractant was completely dispersed into fine droplets which facilitated the mass transfer of the target analytes from sample solution to organic extraction solvent. During the restoration process, the stirring speed was reduced so that a steady and benign vortex formed on the top-center of the sample solution where the dispersed droplets began to concentrate. After several minutes, the dispersed organic phase was separated from the water phase completely and formed a suspended layer. A centrifugation step was thus no longer needed. Under the optimal conditions, the limits of detection for the analytes varied from0.14to0.26μg L-1. The enrichment factors ranged from125-200. The recoveries of the spiked real samples ranged from83.8-105.3%. The proposed approach performed in the experimental set-up can offer many advantages such as high extraction efficiency, good repeatability. In addition, the method required less organic solvent, thus proving to be an environmentally friendly technique. The approach possesses great potential in the rapid analysis of trace fungicides in complicated matrices.(3) A motor stirrer-assisted single drop microextraction (SDME) method was developed for the fast, efficient determination of three fungicides (azoxystrobin, diethofencarb and pyrimethanil) in water and wine samples followed by HPLC. The most attractive features of this technique were firstly using a motor stirrer and a polychloroprene rubber tube (PCR tube) as an extraction vessel. The use of a motor stirrer instead of magnetic stir bar, which enhanced the mass transfer of analytes greatly, thus reduced the time to achieve extraction equilibrium. The PCR tube was used instead of the needle tip of microsyringe to load organic extraction solvent, which could load more extraction solvent due to the larger interfacial tension and increase markedly the stability of microdrop. Another notable feature of the proposed work is that the magnetic stir bar was not used. Under the most favorable extraction parameters, the limits of detection of these fungicides varied from0.25to0.46μg L-1, the enrichment factors were obtained in the range from115to168. The proposed technique was successfully applied to determine three target fungicides in real water and wine samples, where the obtained recoveries were between81.6and100.4%.