Spectrophotometric and Potentiometric Determination of Some Organophosphorus Pesticides in Bulk Powder and in their Dosage Forms

Two simple, sensitive and precise methods were developed and validated for determination of diazinon, chlorpyrifos and temefos pesticides in bulk powder and dosage forms. The spectrophotometric method involves the oxidation of these pesticides with potassium iodate in acidic medium with the liberation of iodine and subsequent extraction with cyclohexane followed by measuring the absorbance at λ=520 nm. Beer`s law is obeyed in the concentration range of 0.05-1.00 mg ml^-1 for diazinon and chlorpyrifos and 0.05-0.6 mg ml^-1 for temefos. The apparent molar absorbitivities of the resulting coloured products are found to be 0.539x10³, 0.368x10³ and 0.474x10³ L mol^-1 cm^-1 for diazinon, chlorpyrifos and temefos, respectively, whereas Sandell sensitivities are 0.5647, 0.9527 and 0.9841 μg cm^-2, respectively. The potentiometric method involves the direct titration of the studied pesticides with N-bromosuccinimide in acidic medium and the end point is determined potentiometricallyusing platinum indicator electrode. The ratio of drug: NBS was 1:3 for diazinon andchlorpyrifos and 1:6 for temefos. The proposed methods were successfully applied to the analysis of the studied pesticides in bulk powder and in dosage forms without interference from other additives.