Validation and kinetic of enzymatic method for the detection of organophosphate insecticides based on cholinesterase inhibition.

Kinetic and validation of the enzymatic method for the determination of fenitrothion organophosphorus based on cholinesterase inhibition were studied. A Linear relationship was obtained with a determination coefficient R2 of 0.9989 suggesting that the noncompetitive inhibition kinetic equation is suitable to represent the enzymatic assay of fenitrothion. The value of the inhibition constant KI was 0.374 μg/ml/min. The analytical logarithmic curve for the determination of fenitrothion concentration using the percentage of cholinesterase inhibition presented good linear relations at concentrations of 0.05-2 μg/ml (R2 = 0.9889). The maximum inhibition 83% was observed at 2.0 μg/ml final assay concentration. The lower inhibition 3.3% was observed at 0.05 μg/ml detection limit. The experimental measurement condition was optimized. The enzymatic method exhibited detection limits (LOD) in the range of 0.05-2.0 μg/ml. The limit of quantification (LOQ) was 0.06 μg/ml with inhibition 13%. The concentration of fenitrothion that inhibited the hydrolysis of substrate by 50% (IC50 value) was 0.4 μg/ml. Standard deviations and coefficients of variation indicate a good precision of the enzymatic method for the detection of organophosphate insecticides at an incubation time of 20 min.