Square wave voltammetry assay of organophosphorus inhibition on cholinesterase in two phases of isooctane/water

A novel method for the detection of pesticides by inhibition of cholinesterase (ChE) from earthworm was developed. Two immiscible phases are employed where the organic phase isooctane contains substrate and the aqueous phase does enzyme. Water insoluble indophenol acetate was hydrolyzed by ChE at the interface of two phases to produce water soluble indophenol. The latter spontaneously penetrates into aqueous solution and gives the change of electrochemical signal. Organophosphorus compounds methyl parathion dissolved in isooctane phase could inhibit the activity of ChE at the interface of two phases and a corresponding inhibition relationship is given in the concentration range of 50 ng/ml–100 μg/ml.