Abstract
Residue analysis of benomyl [methyl 1-(buthylcarbamoyl)-2-benzimidazolecarbamate] and thiophanate-methyl [dimethyl 4, 4-o-phenylene bis (3-thioallophanate] (TM), in various plants and soil were investigated.
Benomyl and TM were converted to MBC (methyl 2-benzimidazolecarbamate) and then determined by high speed liquid chromatograph equipped with a fluorophotometric detector.
Benomyl was extracted from plants with ethyl acetate. The solution was concentrated to about 50ml and then extracted with 0.1N hydrochloric acid. Benomyl was hydrolyzed to MBC in this process. The acidic solution was washed with ethyl acetate and adjusted to pH 6.4, then extracted with dichloromethane. The solution was evaporated and the residue was dissolved in methanol.
Benomyl in soil was extracted with methanol and the solution was evaporated under vacuum. The residue was dissolved in ethyl acetate and to the solution 0.1N hydrochloric acid was added. The acidic solution was treated as that from plants. TM and its degradation product, MBC, in soil were extracted with methanol. The extract was acidified with hydrochloric acid, and TM was extracted with dichloromethane, while MBC remained in aqueous solution. TM was converted to MBC by refluxing with copper acetate in 50% aqueous acetic acid. The reaction mixture was adjusted to pH 6.4 and was extracted with dichloromethane. The dicholomethane solution was evaporated under vacuum, and residue was dissolved in methanol. Chromatography of the methanol solution was performed on a high speed liquid chroromatograph fitted with a Hitachi-Gel # 3010 glass column (3mm×50cm). The column was eluted with methanol and water (19+1). Flow rate was 1.7ml/min. A fluorophotometer with a flow cell (2×20mm) was used as a detector. Wave length for exitation was 285nm and that for emission was 315nm. Interfering and quenching phenomena of fluorescence were not observed.
The lower limit of detection for benomyl in crop and soil were 0.008ppm and 0.01ppm respectively and those for TM and MBC in soil were both 0.03ppm. Recoveries of benomyl were 74-90% in plants and 69-98% in soil, and those of TM and MBC were 75-122% and 62-75% respectively.
