| The instrument anlysis method and field testing method were employed for the investigation 3 of the dissipation dynamics and residues of chlorpyrifos, imidacloprid,spirotetramat and its motablites, difenoconazole, in pear. The samples were extracted with acetonitrile and purified by sodium chloride salting out. Chlorpyrifos was detected by GC/MS/MS, and the other three pesticides were detected by LC/MS/MS. Quantization was performed using external standard method. The results showed that the dissipation dynamics of chlorpyrifos, imidacloprid, spirotetramat and its motablites, difenoconazole, in pear meet the first-degree dynamics matrix. There half-lives were 4.4, 12.2, 13.1 and 10.3 d, respectively. From 7 days after the pesticide application to harvest, the final residues of the above 4 pesticides in pear did not exceed the MRL value of China. According to the recommended application concentration and operating procedures, All four pesticides can be safely used on pears. |