Residue Analysis of Thiophanate Methyl and Its Degradation Products and Metabolites by High Performance Liquid Chromatography

Abstract

A procedure for the determination of thiophanate methyl (TM) and its degradation products/metabolites in some crops is described. Residues of TM, methyl 2-benzimidazol-carbamate (MBC) and two oxygen analogues of TM (OA-1 and OA-2) were simultaneously determined by high performance liquid chromatography. A sample was first neutralized to pH 6.5-7.0 with sodium phosphate, tribasic. Compounds were extracted with methanol and partitioned into ethyl acetate. The ethyl acetate layer was washed with buffered aqueous solution (pH 6.5) to remove methanol. The ethyl acetate solution was dried and evaporated to ca. 10ml. The concentrate was poured into a deactivated alumina column and eluted with ethyl acetate and methanol-water (1:1). TM and its degradation products/metabolites were eluted with aqueous methanol and partitioned into ethyl acetate. The ethyl acetate layer was dried and evaporated to dryness. The residues were dissolved in dichloromethane and injected into HPLC. Two types of normal phase columns (Nucleosil NH₂ and Partisil-10 PAC) were used with a mobile phase consisting of hexane, dichloromethane and ethanol. The minimum detectable limit with a UV detector at 254nm was ca. 5ng for TM and its degradation products/metabolites. Recovery data were obtained by fortifying tomatoes, green peppers, grapes and strawberries with TM, MBC, OA-1 and OA-2 at 0.5ppm levels. Average recoveries of TM, MBC, OA-1 and OA-2 were 75, 104, 70 and 75%, respectively.