| Cyhalothrin is a member of the pyrethroid insecticides with broad spectrum,low toxicity and high efficiency,mainly used for controlling the pests in peanuts,soybeans,cottons, Fruits,and vegetables.Presently,the residual analytical method of this insecticide in soybean is few reported,its national standard method has also not be established.GC is a kind of modern analytical technique which is convinient,fast,high-efficiency and sensitive.In this study,the residual analytical method of cyhalothrin in soybean has been established.Using the established method,the tests of matrix-adaptability in the other lipid materials such as peanut is performanced.The stability of cyhalothrin in diffrerent stored condition is also studied. The main results are as follows:1. GC chromatographic conditionModel Agilient 6890 GC equipped with 63Ni electron-capture detector,the main column is a capillary column,30m×0.25mm(i.d)×0.25μm HP-1;detector temperature:320℃;injector temperature:260℃;column temperature:60℃(hold 1.0min) 25℃min-1 80℃(hold 0.0min) 5℃min-1 200℃( hold 0.0min) 15℃min-1 260℃(hold 7.0 min).Carrier gas is Nitrogen at the flow rate of 3.0 mL/min.2. Extract systemExtract method:The average recoveries from spiked soybean extracted by surging and ultrasonic method are respectively 86.37% and 87.24%,the optimal method is surging.Extracte solvent:The average recoveries from spiked soybean extracted by acetone,acetonitrile,acetone /water(3:1), acetonitrile water(3:1),petrolum ether and hexane are respectively 81.50%,84.15%,86.14%,87.63%,87.82% and 87.35%,the optimal extract solvent is petrolum ether.The quantity of extract solvent:The average recoveries from spiked soybean extracted by petrolum ether at the range of 20~100ml everary 20ml are respectively 69.56%,83.17%,88.28%,89.13% and 88.57%.the optimal quantity of extract solvent is 60mL.Extract times:The average recoveries from spiked soybean extracted by once,twice and 3 times are respectively 86.93%,87.25% and 87.14%,the optimal extract times is once. Extract time:The average recoveries from spiked soybean extracted with surging method by 0.0h,0.5h,1.0h and 1.5h are respectively 26.50%,72.36%,93.75% and 92.42%,the optimal extract time is 1.0h.3. Cleaned-up systemLiquid- liquid extraction times:The average recoveries from spiked soybean purified with liquid- liquid extraction by saturated acetonitrile are respectively 73.54%,85.84% and 86.67%,the optimal times is twice.There are two methods to get rid of the acetonitrile obtained from the LLE step.One method is to back-extract into petrolum ether,the other is to evaporate the acetonitrile directly until dryness.The sorbent filling in column chromatography:The average recoveries from spiked soybean purified with chromatography by filling in Florisil and alumina are respectively 99.42% and 57.39%,the optimal sorbent is Florisil.4. Validation of the methodUsing the establishing method,the average recoveries from spiked soybean with fortified level 0.05mg/kg,0.2mg/kg and 2.0mg/kg are respectively 85.31%,88.72% and 83.75%,the variance coefficient of the recoveries are respectively 7.21%,3.04% and 2.16%.The results are all according with the requirement of residual analysis.5.Matrix-adaptability testUsing the established method,the recoveries of cyhalothrin in fortified peanut at level 0.2mg/kg is 85.42%,CV% is 3.50%.The result is according with the requirement of residual analysis.6. Sensitivity of the methodLOQ is 2.0×10-11g,the minimum detected concentration is 0.005mg/kg.7. Stability testThe standard solution of cyhalothrin(diluted with petroleum ether) at 1×10-5 g/mL can be stored 3 months at 4℃;Cyhalothrin in extract solution of soybean can be stored 15 days at 4℃or at -20℃;Cyhalothrin added in soybean matrix can be stored 30 days at 4℃or at-20℃.
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