Spectrophotometric Determination of Benomyl and Methyl 2-Benzimidazole Carbamate in Product Formulations by a Low Temperature-Solubilization Technique

A rapid spectrophotometric method has been developed to determine benomyl (methyl l-(butylcarbamoyl)- 2-benzimidazole carbamate) and methyl 2-benzimidazole carbamate (MBC) simultaneously in wettable powder formulations by solubilizing all the ingredients in a special solvent mixture. A special solvent mixture consisting of chloroform, dioxane, and water was prepared at room temperature; the mixture was cooled to 1°C and used to dissolve samples. The degradation of benomyl, unavoidable at 25°C, was eliminated by this cold temperature operation. Absorbance of the diluted solution was measured at 294 and 286 nm in a ratiorecording spectrophotometer, and individual concentrations of benomyl and MBC were calculated by a simple equation. An alternative method has been suggested for users of nonautomatic scanning spectrophotometers. re-Butyl isocyanate was used to stabilize benomyl in standard solutions and to re-form benomyl from MBC. Analyses were conducted on Benlate® 50% WP and Benlate® 10% WP mixed with captan 50%. Most 50% WP formulations contained 50-55% intact benomyl and 0.4-2.3% MBC. Benomyl was stable in those WP formulations, although both time and conditions of storage varied significantly. Most 10% WP samples contained 8–12% benomyl and 0.1–2.9% MBC.