Applications of mixing pesticides to control the pests on crops were efficient for the IPM (Integrated pest management). A rapid method to determine the residues of different pesticides in Chinese mustard (Brassica chinensis Linn) by single-step modified QuEChERS method with GC-MS/MS and LC-MS/MS was developed and applied to study the residues in samples following application of individual and a tank-mixed combination of imidacloprid 9.6% SL and chlorpyrifos 40.8% EC in fields. Fast extraction and cleanup of pesticide residues with acetonitrile containing 1% acetic acid, anhydrous magnesium sulfate, sodium acetate, and primary secondary amine sorbent were carried out at the same time. The linearity of the analytical response across the studied range of concentrations (0.01�0.50 mg/L) was excellent, obtaining a correlation coefficient (r2) of >0.999. The limits of quantification (LOQ, S/N=10) of two pesticides ranged from 0.1 to 0.2 ppb. The recoveries of imidacloprid and chlorpyrifos in samples were 84.9-89.4% and 87.3-94.4%, respectively (fortification at 0.1, 0.4 and 0.8 �g/g; RSD: 1.0-6.1%, n=3). The residues of imidacloprid were reduced (0.41-0.86X) and that of chlorpyrifos were increased (1.2-3.0X) in Chinese mustard samples (RSD: 0.7-12.6%, n=3) when treat with a tank-mixed combination of the two pesticides. It showed the same phenomenon at the recommended or higher dose. The dissipation rate of pesticides on Chinese mustard was similar either individual or a tank-mixed combination of pesticides. The half-life of chlorpyrifos and imidacloprid on Chinese mustard was around 3.0 and 6.0-6.4 days, respectively, using the first-order equation.

Comparison of residues in Chinese mustard (<i>Brassica chinensis</i> Linn) following application of individual and a tank-mixed combination of imidacloprid 9.6% SL and chlorpyrifos 40.8% EC in fields

248th National Meeting (2014)

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Comparison of residues in Chinese mustard (Brassica chinensis Linn) following application of individual and a tank-mixed combination of imidacloprid 9.6% SL and chlorpyrifos 40.8% EC in fields