Preparation Of Magnetic Composites And Their Application In Determination Of Herbicide Residues In Rice

Sample preparation is the critical process in chromatographic analysis.It not only allows the target analytes to be extracted and enriched,but also can further eliminate the interference in extracts.Although many kinds of sample pretreatment methods have been developed in recent years,magnetic solid-phase extraction（MSPE）based on solid-phase extraction is particularly noticeable since MSPE makes the procedure of extraction to be fast,simple and easy.In MSPE,magnetic materials or composites,which can be separated easily from sample solutions by using an external magnet,are usually used as adsorbents for the adsorption of target analytes.In this thesis,Fe₃O₄ magnetic nanoparticles were prepared by co-precipitation method.Then,two kinds of magnetic composites were synthesized and applied to the detection of herbicide residues in rice.The specific research contents are as follows:（1）Cyclodextrin-silica modified Fe₃O₄ magnetic nanoparticles（Fe₃O₄@SiO₂-β-CD）were prepared and characterized by vibrating sample magnetometer,scanning electron microscopy and transmission electron microscopy.It is employed as an adsorbent for MSPE of three triazine herbicide residues in rice.Analytical results obtained by high performance liquid chromatography（HPLC）show that limits of detection（LODs）and quantitation（LOQs）of the present method for the three triazine herbicides were in the range of 3.05-4.77μg kg^-1 and 10.18-15.89μg kg^-1,respectively.Extraction recoveries of the three triazine herbicides were 74.2-89.4%with relative standard deviation less than 9.6%.Little difference between the extraction recoveries of all target analytes obtained by reutilizing an adsorbent in MSPE for 12 times indicates the good recycling performance of the synthesized Fe₃O₄@SiO₂-β-CD.（2）The aminated magnetic core-shell silica ball is connected to the graphene oxide layer through an amide bond,and then the hydrothermal synthesized MIL-101（Cr）is combined with magnetic particles above to prepare magnetic MIL-101（Cr）by in-situ magnetization method.The synthesized magnetic MIL-101（Cr）was utilized as magnetic solid-phase extraction（MSPE）adsorbent for the extraction of seven triazine herbicides in rice.The results obtained by high performance liquid chromatography show that the limits of detection（LODs）and quantitation（LOQs）of seven triazine herbicides were 0.010-0.080μg kg^-1 and 0.05-0.28μg kg^-1 respectively,The recovery of rice samples was 83.9-103.5%with relative standard deviation（RSD）less than8.7%.The in situ reaction simplifies the operation,and also can get higher extraction recovery.