DETERMINATION OF ORGANOPHOSPHATE AND CARBAMATE PESTICIDES USING A COBALT PHTHALOCYANINE-MODIFIED CARBON PASTE ELECTRODE AND A CHOLINESTERASE ENZYME MEMBRANE

An amperometric biosensor for the detection and determination of organophosphate and carbamate pesticides is based on a cobalt phthalocyanine-modified carbon paste electrode covered with a cholinesterase enzyme membrane. The electrode poised at +400 mV (vs. Ag/AgCl/3 M KCl) oxidizes thiocholine formed by butyrylthiocholine hydrolysis in the glutaraldehyde-cross-linked cholinesterase layer. The activity of cholinesterase is non-competitively inhibited in the presence of pesticides. A linear relationship exists between the relative decrease in steady-state current after the addition of a sample and the inhibitor concentration. This method of evaluation allows the repetitive use of an enzyme membrane; twenty analyses can be carried out with a single cholinesterase membrane. The sensitivity varies from 0.181 (Hostaquick) to 0.00136 s-1 g-1 l (Seedox); detection limits are 0.3 and 80 mg l-1, respectively, for these two pesticides. The determination of eleven pesticides is demonstrated.