Research On Detection Methods For 20 Kinds Of Pesticide Residues In Grain

A simple, sensitive and rapid analytical method was developed to simultaneously determine multiple pesticide residues in cereal. The samples were extracted by acetonitrile,cleaned up by different sample treatment methods, C18 SPE column, GPC and modified QuEChERS, and then analyzed by GC- MS/MS in selective reaction monitoring(SRM)mode. The pesticides were identified with retention time, selected ions and their relative abundances, and they were quantified based on extract of spiking standards in a blank sample,aim to find a ideal analytical method.Comparison of the three treatment methods were investigated on performances including purifying effect, matrix effect, solvent consumption, clarification time and recovery of the 20 kinds of pesticides. The results indicated that it was easy operating, time-saving, high precision and reproducibility by C18 SPE column, but the cost is higher. The purification effect of GPC method was good, but this method used a large amount of solvent and have low recovery. QuEChERS purification method was time-saving and labor-saving, less solvent consumption, less pesticide losses and high recovery, but the purification effect was worse.Using GC-MS/MS under the same detection condition, test the rate of recovery of pesticides in the liquid samples purified by the three purification method. The results indicated that,using the three purification methods, the linear range was between 0.01 μg/mL and 0.2 μg/mL of each pesticide,the linear correlation coefficients were greater than 0.99. Most of the spike recoveries of three concentration levels(0.01, 0.05 and 0.2 mg/kg) were in the range of 70 %to 120 % and the RSDs of the 20 pesticides were less than 20 %. They can meet all the requirements of national residues level. While using GPC purification, the recovery of a few of pesticides were too low, can not satisfy the requirement of accuracy.In summary, the best experiment conditions was eluting the C18 column by 20 mL acetonietrile, then put the C18 column in the support bracket, and put a heart-shaped bottle under it. Then eluting by another 20 m L acetonietrile, collect the extract and eluent, put it on the rotary evaporator(48 ℃, 110 r/min) until the liquid was dry. After cooling to room temperature, dissolved in 2 mL acetone. QuEChERS purification: purified 10.0 g grainsamples, using 50 mg PSA powder, 150 mg anhydrous magnesium sulfate and 50 mg C18 powder.The experimental results showed that the method can be used as a routine analysis and confirmatory method for detecting different kinds of pesticide residues in grain. At the same time, in this method, special parent ions were isolated from others, each parent ions was matched one-for-one with daughter ions, so it had strong background anti-interference ability.The gas chromatography tandem mass spectrometry conditions have been confirmed to be a good means for analysis positive samples. Two kinds of purification has became the detection method of Liaoning Entry-Exit Inspection and Quarantine Bureau daily monitoring of pesticide residues in cereals, and achieved good results.