Simultaneous Determination of Vamidothion and Its Oxidation Metabolites in Potatoes and Apples by Gas Chromatography

A method for simultaneous determination of vamidothion (V0) and its oxidation metabolites vamidothion sulphoxide (V1) and vamidothion sulphone (V2) in potatoes and apples has been developed. Fifty grams of a sample was homogenized and extracted with acetone followed by evaporation to remove the acetone. To the residual aqueous solution, a 10% sodium chloride solution was added, and the coextractives were eliminated by washing the aqueous solution with 10% ethyl acetate in hexane. Then, V0, V1, and V2 were extracted from the aqueous solution using dichloromethane. The organic layer was evaporated to dryness and filled up to 2 ml with ethyl acetate. Two microliters of the extract were injected into gas chromatograph-mass spectrometer set for selected ion monitoring. The column used was a CBP-1 capillary column (0.2 mm inside diameter × 15 m, 0.25 μm film thickness). Gas chromatographic conditions were investigated in detail and only nonpolar capillary columns gave satisfactory results. The retention time of undecomposed V1 has been reported for the first time. The recoveries for the fortified potatoes and apples were 93-109% for V0, 62-108% for V1, and 64-89% for V2, when they were fortified at levels of 0.01-5.0 ppm. Detection limits were 0.01, 0.2, and 0.05 ppm for V0, V1, and V2, respectively.