Detection and separation of cypermethrin, deltamethrin and fenvalerate by thin layer chromatography

Synthetic pyrethroids like Cypermethrin, Deltamethrin and Fenavalerate containing -cyano ester group in their molecule are separated by TLC and detected by a new chromogenic reagent, viz. alkaline p-nitrobenzaldehde. Freshly prepared 1 gm % alcoholic p-nitrobenzaldehyde and 10% sodium hydroxide produced violet spots with these three pyrethroids on TLC plates. The lowest limit of detection is 1–5 ug and the colour of spots it stable for 5 minutes. The reagent has been used successfully for synthetic pyrethroids identification in biological tissue in forensic toxicology. The chemical reaction involved is the formation of cyanohydrin by the action of sodium hydroxide on cyano ester group in the pyrethroids, which in its turn reacts with p-nitrobenzaidehyde to produce a violet coloured product by Benzoin condensation.