Development of New Kinetic-spectrophotometric Method for Determination Insecticide Dimethoate in Milk and Water

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 inhibited effect of dimethoate on the oxidation of sulphanilic acid (SA) by potassium periodate in acetate buffer in presence Fe(III) ion and 1,10-phenantroline. Dimethoate was determined with linear calibration graph in the interval from 28.10 to 196.70 ng/mL. The optimized conditions yielded a theoretical detection limit of 21.64 ng/mL based on the 3S(b) criterion. The RSD is 4.85-1.2% for the concentration interval of dimethoate 28.10-196.70 ng/mL. The reaction was followed spectrophotometrically at 368 nm. The kinetic parameters of the reaction are reported, and the rate equations are suggested. The developed procedure was successfully applied to the rapid determination of dimethoate in spiked milk and water samples. Liquid-liquid extraction and solid-phase extraction (SPE) was used for extraction of dimethoate from milk and water samples with Chromabond (R) (Macherey-Nagel) C18 cartridges. The HPLC method was used like an comparative method to verify the results. The results obtained by two different methods showed good agreement.