Determination of trace dimethoate in milk and river water by kinetic spectrophotometry using malachite green and potassium periodate

摘要

In the present study, a new sensitive and simple kinetic-spectrophotometric method for the determination of the insecticide dimethoate [O,O-dimethyl-S-(N- methyl-carbomoylmethyl)-phosphoro-dithioate] is developed. The method is based on the inhibition effect of dimethoate on the oxidation of malachite green (MG) by potassium periodate (KIO _4) in the presence of Mn(II) ions. Inhibition kinetics of this catalytic reaction was investigated in the presence of dimethoate and the possibility of its analytical application was evaluated. The important variables that affected the reaction rate were investigated and the optimum conditions giving maximum sensitivity were established. Dimethoate was determined with linear calibration graph in the interval from 4.58 to 41.22 μg/mL. The optimized conditions yielded a theoretical detection limit of 1.24 μg/mL based on the 3S _b criterion. The RSDs of the method (n = 5) were 1.2-4.9% for the concentration interval of dimethoate from 4.58 to 41.22 μg/mL. The reaction was monitored spectrophotometrically by measuring the change in absorbance over time at 615 nm. The method was applied to the determination of dimethoate in waters and milk, and was compared with the spectrophotometric method. The quantitive method developed on the basis of inhibition kinetics is practical, fast and economical. For this reason, it is open for new application fields.