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We studied the simultaneous determination of demeton-S-methyl, oxydemeton-methyl, and their oxide demeton-S-methylsulfone, in agricultural products by liquid chromatography coupled with mass spectrometry (LC-MS). The sample homogenized with antioxidants L-ascorbic acid and butylhydroxytoluene was extracted with acetone. An aliquot of the crude extract was reextracted with ethyl acetate by using an EXtrelut column. After hexane/acetonitrile partitioning lipid-rich samples such as cereals, the extract was cleaned up on a PSA column or tandem graphitized carbon/PSA column, and determined by ESI-SIM mode LC-MS. Average recoveries (n=5) of compounds from ten kinds of samples fortified at the analyte concentration of 0.05 microg/g were from 73.8% to 102.5%, and the relative standard deviations were

We evaluated a multiresidue method for determination of pesticides in agricultural products by SCAN mode GC/MS coupled with three kinds of database for 253 pesticides: relative retention time, mass spectra and calibration curve (SCAN method). Twenty-six pesticides, a total of 131 pesticides were detected in samples by the SCAN method. The detection results agreed closely with those of the SIM mode GC/MS method using calibration standards (SIM method). The ratios of the SCAN method to the SIM method ranged from 0.3 to 3.1 with SD values of 0.63. It was judged that the SCAN method could be applied to the screening analysis of pesticide residues in agricultural products, provided that the sample preparation method makes it possible to effectively remove sample matrixes with minimal loss of analytes.