Development And Application Of Magnetic Microextraction Techniques For Analysis Of Pesticide Residues In Foodstuffs

In order to improve the yield and quality of agricultural products, pesticides are widely used to control weeds, diseases and pests in modern agriculture. However, excessive use of pesticides might occur the chemical contamination of soil, environmental water and agricultural products. Therefore, the development of extraction and determination techniques for the analysis of pesticide residues in foodstuffs become an important issue today.In this thesis, two common pesticides, pyrethroids and triazine herbicides, were selected as analytes. Magnetic microextraction coupled with ultra fast liquid chromatography was applied for the extraction and determination of the analytes in different foodstuffs.Polyaniline-coated magnetic particles-based magnetic solid phase extraction（MSPE） was developed for extracting pyrethroids from tea drinks. The magnetic particles were prepared via hydrothermal reaction and solvothermal reaction,and characterized by scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry, then were used as the adsorbent in magnetic solid phase extraction of five pyrethroids in tea drinks. The ultra fast liquid chromatography was applied to the separation and determination of the analytes. The effects of several experiment factors on the extraction effciency, including the amount of prepared particles, the p H value, the time of ultrasound extraction, and the conditions of desorption, were investigated. The limits of detection and the limits of quantification were 0.025-0.032 ng m L-1 and 0.083-0.106 ng m L-1, respectively. Recoveries obtained by analyzing the real tea drinks were in the range of 72.06-118.41 %, with the relative standard deviations（RSD） lower than 8.1%. The magnetic particles could be reused easily after simple washing with methanol and deionized water.Magnetic ionic liquid-based dispersive liquid-liquid microextraction（MILDLLME） was developed for extracting triazine herbicides from vegetable oils. The MIL, 1-hexyl-3-methylimidazolium tetrachloroferrate（[C6mim][Fe Cl₄]）, was used as the microextraction solvent. The magnetic separation time was shortened by simply mixing carbonyl iron powders（CIP） and MIL in the sample after DLLME. The effects of experimental parameters, such as the amount of MIL, ultrasound extraction time, cleanup solvent and the volume of cleanup solvent were investigated. The present MIL-based DLLME in combination with ultra fast liquid chromatography（UFLC） gave the limits of detection of 1.31-1.49 ng m L-1 and limits of quantification of 4.33-4.91 ng m L-1 for six triazine herbicides. When the present method was applied to the analysis of real vegetable oil samples, the obtained recoveries were between 81.8% and114.2% and relative standard deviations were lower than 7.7%. Compared with existing methods, the performances achieved by the present method were acceptable.Matrix solid-phase dispersion coupled with magnetic ionic liquid dispersive liquid-liquid microextraction（MSPD-MIL-DLLME） was developed for the extraction of six triazine herbicides from oilseeds. The MIL, 1-butyl-3-methylimidazolium tetrachloroferrate（[C4mim][Fe Cl₄]）, was used as the microextraction solvent, and magnetic separation was employed to simplify the separation procedure. By this method, the extraction and the cleanup of analytes could be accomplished in one step. The effects of several important experimental parameters, including the type of dispersant, the ratio of sample to dispersant, the type and volume of collected elution solvent, the type and the volume of MIL, were investigated. The MSPD-MIL-DLLME in combination with ultra fast liquid chromatography gave the limits of detection of 1.20-2.72 ng g-1 and the limits of quantification of 3.99-9.06 ng g-1 for triazine herbicides. When the present method was applied to the analysis of real oilseed samples, the recoveries of the analytes ranged from 82.9-113.7% and the relative standard deviations（RSDs） lower than 7.7% were obtained. The present method is easy-to-use and effective for extraction of triazine herbicides from oilseeds, and shows the potentials of practical applications in the treatment of fatty solid samples.In situ magnetization ionic liquid-based dispersive liquid-liquid microextraction（In situ MIL-DLLME） using quaternary ammonium-based ILs as the microextraction solvent, was developed and applied to the extraction of four triazine herbicides from vegetable oils. After the establishing of the extraction equilibrium, Ni Cl2·6H2O was employed as the magnetization agent to transform the nonmagnetic ILs into the magnetic ILs by a simple in situ reaction, which realized the combination of IL-DLLME and magnetic separation. The effects of several important experimental parameters, including the type and amount of quaternary ammonium salt, the ultrasound extraction time, the type and the amount of transition metal salt, the type and the volume of cleanup solvent, were optimized. The In situ MIL-DLLME in combination with ultra fast liquid chromatography gave the limits of detection of 1.21-2.89 ng g-1, and the limits of quantification of 4.00-9.52 ng g-1 for triazine herbicides. When the present method was applied to the analysis of vegetable oil samples, the recoveries of the analytes ranged from 80.5-118.5% and relative standard deviations lower than 9.7% were obtained. The in situ reaction could simplify the extraction procedure and expand the range of selection of ionic liquids. In addition, magnetic separation could also be applied in cleanup procedure.