A New Spray Reagent for Selective Detection and Quantification of Dichlorvos in Bluish Tinged Maize Grains by TLC-Spectrophotometry

摘要

A new spray reagent has been used for TLC detection and spec-trophotometric quantification of dichlorvos after extraction with ethanol from bluish tinged maize grains. Silica gel G as stationary phase with cyclohexane-acetone-methanol 8:3:0.5 (v/v) as mobile phase was identified as the best TLC system for detection and migration (R_F) of dichlorvos. On alkaline hydrolysis dichlorvos forms dimethylphosphoric acid and dichloroacetaldehyde; the latter reacts with 2-thiobarbituric acid to give a sharp pink spot. The reagent is selective for dichlorvos, and does not react with other organophosphorus, organochlorine, carbamate, and synthetic pyrethroid insecticides. The constituents of viscera (amino acids, peptides, proteins, etc.) and grain do not interfere with the test. The lower limit of detection on silica TLC plates was 18 ug. The absorbance maximum (lambda_(mal)) of the pink color formed by dichlorvos was 500 nm. A plot of absorbance against concentration was a straight line passing through the origin and obeying the Beer-Lambert law in the concentration range 50-350 mug mL~(-1). The method has been used for identification of dichlorvos in cereals, pulses, vegetables, and fruit.