Application of Gas Chromatograph Equipped with FPD for the Determination of Methyl Thiophanate, the Metabolites and Mono-sec-butylamine

Abstract

A simultaneous detection and determination procedure of thiophanate methyl, its metabolites (methyl benzimidazole carbamate; MBC, aminobenzimidazole; AB) and mono-sec-butylamine; BA) were established.
These fungicides or insecticides are widely used in the cultivation of vegetables and fruits. Thiophanate methyl is known to be metabolized in plants remaining in the form of MBC and AB.
In order to elevate the detection level of these compounds, benzenesulfone derivatives of them were prepared, which were then subjected for the gas chromatographic determination by use of an FPD-gas chromatograph. Ethyl acetate was adopted as the extracting solvent of these compounds from plants. Because of the volatility of BA, it was impossible to concentrate ethyl acetate extract, and so the latter clean-up was carried out by use of alumina column chromatography (Merck Art. 1097 Aluminiumoxid standardisiert was chosen), applying ethyl acetate and methanol-water mixture (5:5) as eluant, in turn. Methanol water fraction was collected making each 15ml as one fraction. It was confirmed that the above-mentioned compounds were eluted almost all into Fraction No. 2 of methanol-water mixture. The fraction was extracted again with ethyl acetate and, after benzenesulfonation, the derivatives were concentrated and injected into an FPD-gas chromatograph. The conditions finally adopted are as follow. Column ∅3mm×75cm in length packed with 1.5% SE-30 on Chromosorb G60/80, column temperature: 165°C for the detetion and determination of BA and TPM (thiophanate methyl), 200°C for the detection and determination of MBC and AB.
The detection level was 0.01ppm for BA, 0.02ppm for AB and MBC and 0.04ppm for TPM. Recoveries of these compounds from orange peel and cucumber were about 90% in case spiked on 0.5ppm level, while 80-85% spiked on 0.1ppm level.