Gas Chromatographic-Mass Spectrometric Characterization of an Alteration Product of Malathion Detected in Stored Rice

Abstract

Four alteration products of malathion have been observed in crop extracts of rice, which may not be readily identifiable in a typical gas chromatographic-mass spectrometric (GC-MS) analysis of the residues. Extracts of rice containing malathion and several related compounds were analyzed on gasliquid chromatographic (GLC) columns of different polarities. The methyl ethyl succinate ester of malathion co-elutes with malaoxon from a nonpolar GLC column. Retention data and GC-MS analysis indicate the presence of 3 previously reported compounds. Evidence was obtained for a fourth compound, O-methyl O-ethyl S-(l,2-bis-carbethoxy) ethyl phosphorodithioate, apparently resulting from the environmental alteration of malathion.