DETERMINATION OF INSECTICIDE, [O-(4-BROMO-2,5-DICHLOROPHENYL) O-METHYL PHENYLPHOSPHONOTHIOATE] (VELSICOL VCS-506), ITS OXYGEN ANALOG, AND ITS PHENOLIC HYDROLYSIS PRODUCT IN CORN AND MILK BY GAS CHROMATOGRAPHY

A method was devised for determining residues of Velsicol VCS-506 [O-(4-bromo-2,5-dichlorophenyl) O-methyl phenylphosphonothioate], its oxygen analog, and its phenolic hydrolysis product in corn and milk. The compounds are separated by liquid chromatography of the extract on two columns, buffer-deactivated silica gel and alumina, prior to gas chromatographic analysis using a flame-photometric detector for the parent compound and the oxygen analog and a Ni63 electron-capture detector for the phenol. Recoveries of the parent insecticide and its oxygen analog added at levels between 0.05 and 5.0 p.p.m. were 91 to 99% and 72 to 92%, respectively. Recoveries of the phenol were 55 to 69% from corn and 93 to 95% from milk. Minimum detectable levels for the three compounds were less than 0.01 p.p.m. © 1969, American Chemical Society. All rights reserved.