Detection of organophosphorous pesticides with an immobilized cholinesterase electrode.

A simple and reliable method based on cholinesterase inhibition is proposed to detect organophosphate pesticides in water. The potentiometric method to measure enzymatic activity was applied to an immobilized cholinesterase film coupled directly to a flat glass pH electrode. Under controlled laboratory conditions, it was possible to correlate inhibition of cholinesterase activity with intramembranal pH shifts induced by substrate hydrolysis. Measurements can be performed with such an enzyme electrode system in real time by monitoring the inhibition process, or after incubation of the enzymatic film. Technical grade compounds of methylparathion, azinphosethyl , and mevinphos were used as examples, and detected from ppm to several ppb after oxidative treatment. The sensitivity of the enzyme sensor depends on the inhibitory power of the pesticide molecules, and therefore determines additional toxicity information unavailable from other physico-chemical methods. This type of sensor could be used for screening purposes in the detection of pesticides in water pollution control and is intended to be complementary to existing analytical methods.