Abstract: [Objective] By selecting the appropriate analytical chromatographic column,the pretreatment process of the sample was simplified,and the suitable ion pairs were selected for monitoring,the sensitivity and accuracy of the method were improved. [Method] The parallelism （precision）of the samples,the recovery rate of spiked samples（accuracy）,and the detection limit of the method were determined to verify the detection method. [Result] The recovery rates of methyl chlorpyrifos added to milk were 105.3%,106.9% and 108.2%,and the coefficients of variation at the three addition levels were 1.61%,3.06% and 2.52%. The recovery rate of methyl parathion added to milk powder were 100.3%,89.8% and 88.5%,and the coefficients of variation at the three addition levels were 2.14%,1.97% and 1.82%. [Conclusion] The precision and accuracy of this method met the requirements and it could be used for the determination and quality control of daily methyl chlorpyrifos residues in milk and milk powder.

Key words: methyl chlorpyrifos, gas chromatography-mass spectrometry/mass spectrometry combined instrument, milk, milk powder