| Nowadays, all levels of government and the broad masses pay close attention to pesticide residues in food due to the abuse of pesticides and the prosperity of import and export trade in our country. Pesticides residues had attracted more and more attention in present years. Pesticides used in citrus effectively improved the producing yield, but also influenced the quality of the citrus and brought pollution to the environment. Traditional determination method only for single residue could not meet the need of the nowadays laboratory. A fast, simple,inexpensive,non-pollution to environment and effective matrix component remove method for determination for multi-residues is essential for laboratory.In 2003, Anastassiades and Lehotay, et al. from the eastern regional research center of United States agricultural department developed a fast and easy multi-residue method employing acetonitrile extraction/partitioning and "Dispersive solid-phase extraction" for the determination of pesticide residues in produce. The method, compared to other methods has the advantage of quick, easy, cheap, effective, rugged, and safe known as QuEChERS method. Later on, this QuEChERS method became AOAC Official. Accordingly, study on the critical steps in QuEChERS method and improve it, made it fit for our needs in multi-pesticides residue have important means. The main object in our study is to discuss the critical factor impact the results, choose the most popular used pesticides in our county and the pesticides on the routine monitoring list of ago-products quality as our research targets and develop an adaptive method based on the QuEChERS. Method for the determination of multi-pesticides residue in citrus, details are as follows:(1) Comparing was conducted between extract solvents, amount of salt and dispersive sorbent used in pretreatment and its effect on cleanup. Results as follows:the sample amount:anhydrous magnesium sulfate:salt is 10:4:1. The dosage of adsorbent PSA. GCB is 60mg and 0mg.With 1mL acetone and cyclohexane (3:7) capacity after extract second centrifugal.(2) Pesticide residues were determined by GC/MS, retention time and total current Chromatograms were obtained by Scan Program. One target ion and tow or three quality ions were obtained by SIM program to minimize the back ground to improve the sensitivity of the determination.(3) Matrix-induced effects were reviewed between standard and matrix standard. A method for compensation for matrix-induced effects to reduce the error for quantitative analysis was carried out. Experimental results show that 94% of pesticides has matrix enhanced. cephate,dimethoate,fenitrothion,methidathion,imazalil,triazophos,phosmet,Fenpyroximate,propargite and dicofol had obvious matrix-induced effect.(4) Develop a GC-MS method based on the QuEChERS procedure to determinate 55 kinds of pesticide residues in citrus; the linearity, precision and accuracy were investigated. The mean recoveries of all pesticides were in range from 71% to 119%, relative standard deviation were from 1.73% to 17.08% at the 19 pesticides is 0.1 mg/kg,0.4 mg/kg and 0.8mg/kg; 22 pesticides is 0.025 mg/kg,0.1 mg/kg,0.2 mg/kg,4 pesticides is 0.005 mg/kg,0.02 mg/kg,0.04 mg/kg Spike level, the precision and accuracy of this method meet the requirement of residue analysis. The limit of determination of 55 kinds of pesticides is between 0.751μg/kg-5.556μg/kg, limit of quantity is between 2.380μg/kg-18.890μg/kg.
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