Collaborative study of a method for the analysis of dry methoxychlor formulations

A collaborative study has been completed on a method for determining methoxychlor content in dry formulations. The method is based on a total halogen determination plus a selective, qualitative thin lay chromatographic (TLC) measurement to establish the p,p'-methoxychlor is the primary halogen-containing organic species present in the formulation. After extraction of the sample with toluene, the toluene solution of methoxychlor is treated with sodium biphenyl to convert all halogen to the halide. The halide is then extracted with a solution of nitric acid and titrated with silver nitrate according to the Volhard procedure or potentiometrically, using a pH meter assembly. Based on the results obtained from 7 collaborators, the standard deviation of the method is about 0.48% at the 50% level. The qualitative TLC measurement is made on an aliquot of the initial toluene extract, using a selective halogen detection system. The method has been adopted as official first action.