DETERMINATION OF PHORATE AND 5 OF ITS METABOLITES IN CORN

Residues of the insecticide phorate, {O,O-diethyl S-[(ethylthio)methyl] phosphorodithioate), and five of its metabolites were determined in corn treated with the insecticide in granular form. The plant was extracted in a Soxhlet apparatus for 8 hours with 10% methanol in chloroform, and the extract was separated into three fractions by liquid chromatography on silica gel. Aliquots of the concentrated fractions were injected into a gas chromatograph equipped with a flame photometric detector sensitive to phosphorus. No interference from the crop extracts was encountered. Recoveries of the compounds from fortified samples were 96% or more, except for the oxygen analog of phorate; its recovery was only 62%. Sensitivity was 0.004 p.p.m. or better. Residues in various parts of corn plants treated with 1 pound of phorate per acre were determined at seven intervals after application. The toxicities of the six compounds to the European corn borer, Ostrinia nubialis (Hübner), were determined. Partition and chromatographic data are also given. © 1969, American Chemical Society. All rights reserved.