SENSITIVE DETERMINATION OF METHOMYL IN BLOOD USING GAS-CHROMATOGRAPHYMASS-SPECTROMETRY AS ITS OXIME TERT-BUTYLDIMETHYLSILYL DERIVATIVE

A sensitive, selective and reliable method was developed to determine methomyl (methyl-N-[(methylcarbamoyl)oxyl]thioacetimidate), a carbamat e insecticide in human blood, using gas chromatography-mass spectromet ry. Dimethylglyoxime served as an internal standard (I.S.). Methomyl i n the blood was converted to its oxime form by sodium hydroxide. The s olution made acidic with hydrochloric acid was poured into a column pa cked with Extrelut. Methomyloxime and I.S. were eluted from the column with a mixture of dichloromethane-ethyl acetate-chloroform (65:25:10) , transformed to tert.-butyldimethylsilyl derivatives, and analyzed by gas chromatography-mass spectrometry in the electron impact mode. The calibration curves were linear in the concentration range from 1 ng/g to 100 ng/g and 100 ng/g to at least 5000 ng/g. The lower limit of de tection was 0.5 ng/g. The absolute recoveries were 72-93% and within-d ay coefficients of variation were 3.1-5.6% at blood concentrations of 10 and 1000 ng/g. Two practical forensic applications are described. ( C) 1998 Elsevier Science B.V. All rights reserved.