| Oil crops are rich in oil and mainly used for oil extraction purposes. They have been the main raw materials in the modern food industry. Oil crops and vegetable oils obtained by pressing oil crops are necessities of human life. Nowadays, people pay more attention to food safety. Therefore, it is necessary to establish analytical methods for the determination of related substances for quality control of oil crops and vegetable oils. In this work, two new types of material were used in sample pretreatment for analysis of neonicotinoid insecticides in oil crops and phenolic acids in vegetable oils. The thesis is divided into three chapters, the contents are as follows:Chapter 1: Modified graphene and magnetic materials used in the sample preparation were reviewed, and the background, purpose and content of this work were elaborated.Chapter 2: Methylamine modified graphene(CH3NH-G) was synthesized and used as solid-phase extraction(SPE) sorbent to cleanup the acetonitrile extract of sunflower seeds for the determination of neonicotinoid insecticides by ultra high performance liquid chromatography tandem mass spectrometry. The effects of the type of extraction solvent, p H, the amount of CH3NH-G sorbent as well as the type and volume of eluent on the extraction efficiency were evaluated. The regeneration condition for the CH3NH-G SPE cartridge was optimized. Good linearity was obtained for the analytes with correlation coefficients above 0.9986. The limits of detection(S/N=3) and the limits of quantitation(S/N=10) were in the range of 0.053-5.7 ng/kg and 0.18-19.1 ng/kg, respectively. Recoveries were between 74.3% and 119.1%. Relative standard deviations(RSD) for eight replicate determinations were in the range of 1.66-2.86%. This method has been applied to the analysis of 3 kinds of sunflower seed samples from local market.Chapter 3: A novel application of dispersive microextraction based on “Magnetic Water”coupled to HPLC-UV for the fast determination of phenolic acid in vegetable oils was presented. In the present study, Fe3O4 magnetite nanoparticles(Fe3O4 MNPs) were synthesized via a solvothermal process,and a trace amount of water(extractant) was adsorbed on bare Fe3O4 by hydrophilic interaction to form “magnetic water”. Several parameters affecting the extraction efficiency were investigated, including p H and volume of extractant,time of extraction and desorption, and volume of desorption. With 1% formic acid aqueous solution(A): acetonitrile(B) = 85:15(V/V) as the mobile phase, four target compounds(chlorogenic acid, caffeic acid, p-coumaric acid and ferulic acid) were separated completely and detected at 320 nm. Under the optimal conditions, the proposed method got satisfactory correlation coefficients(R>0.99988). The detection and quantification limits at ppb levels(1.2-4.0 ng/g and 3.8-14ng/g, respectively) were obtained. The recoveries at low, medium and high levels were between 71% and 117.8%, and the enrichment factor was from 41 to 51. The relative standard deviations of repeatability for eight replicate determinations were in the range of 3.6%-5.2%. RSD values of reproducibility for six replicate determinations were in the range of 5.9%-8.8%. The established method was successfully applied for the determination of phenolic acids in four vegetable oils. |
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