Further improvement of the modified spectrophotometric method for the determination of malathion

Abstract

A recently described modified spectrophotometric method for the determination of malathion has distinct advantages over all the existing spectrophotometric methods. It suffers from only one drawback in that an expensive spectrophotometer has to be used for the method to be of reasonable sensitivity. This is so because the absorption peak of the bismuth complex of dimethyldithiophosphate (the hydrolysis product of malathion) occurs in the ultraviolet region (325 nm). The method described in this paper is an improvement of that modified method but one in which an additional step has to be carried out and the final measurement of the absorbance of an orange-yellow solution is made at 495 nm. The improvement involves a ligand exchange reaction in which the bismuth-dimethyldithiophosphate complex is transformed quantitatively into the bismuth-dithizone complex.