A new spray reagent for the detection of synthetic pyrethroids containing a nitrile group on thin-layer plates

This paper describes a new spray reagent for selective detection of synthetic pyrethroids containing alpha-cyano group i.e. lambda-cyhalothrin, deltamethrin, cyfluthrin and fluvalinate by thin layer chromatography. These synthetic pyrethroids on alkaline hydrolysis, yield a cynohydrin derivative which degrades to give HCN and a corresponding aldehyde. This liberated HCN reduces 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to formazan, a pink product in the presence of phenazonium methosulfate (PMS). The pink colour formed remain stable for more than 24 h. Other group of insecticides like organophosphorus, organochlorine and carbamate do not interfere in the determination. Pyrethroid insecticides not containing hydrolysable nitrile group also do not interfere. The limit of detection is from 0.5 to 1 mug.