Automated differential screening method for organophosphorus pesticides

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Abstract
An automated enzymic procedure is presented for the detection and determination of organophosphates showing an anti‐cholinesterase activity in vitro. The method is based on the acetylthiocholine‐DTNB (5,5‐dithiobis2‐nitrobenzoic acid) technique of Ellman et al. and can be used for differential analyses by determining the anti‐cholinesterase activity with different sources of cholinesterase and different thiocholine esters before and after oxidation of the samples with bromine water.With quail's serum as the source of enzyme the detection limits are: malathion 5 × 10−2 ppm, mevinphos 5 × 10−3 ppm, DDVP 1 × 10−3 ppm, parathion 2 × 10−4 ppm, and diazinon 1 × 10−4 ppm.The method can be applied to the screening of lettuce without requiring any clean‐up of the extracts.