Multiresidue Method for Determination of Pesticide Residues in Processed Foods by GC/MS

A rapid and simple multiresidue method has been established for determination of pesticide residues in processed foods by GC/MS. The pesticides were extracted with ethyl acetate in the presence of anhydrous MgSO4 in a disposable tube, using a homogenizer. The extract was concentrated and reconstituted in hexane, followed by acetonitrile-hexane partition to remove lipids. The acetonitrile layer was cleaned up with a double-layered SPE cartridge column (graphite carbon black/PSA silica gel). After removal of the solvent, the residue was dissolved in acetone. The test solution was subjected to GC/MS in the EI mode. Recovery tests of 222 pesticides from five kinds of processed foods (dumpling, curry, French fries, fried chicken, fried fish) were performed at two different fortification levels of 0.02 and 0.1 mu g/g, and 100 pesticides showed acceptable recovery (70-120%) with low relative standard deviation (<= 20%) at both concentrations. A survey of pesticide residues in 75 commercial processed foods was carried out. Chlorpropham was detected at 0.04 ppm in a sample of French fries.