Spectrophotometric determination of diquat and paraquat in aqueous herbicide formulations

Abstract

Methods are described for determining diquat and paraquat, singly and in admixture, in formulations. For determining diquat, ultraviolet absorptiometry at 310 mµ in a sodium acetate buffer solution at pH 4·05 is adopted. Paraquat is determined in a diluted solution by measuring the optical density, at 600 mµ, of the blue free radical produced by reduction with alkaline sodium dithionite. For analysing mixtures containing both diquat and paraquat, these methods are combined and use is made of a base-line correction procedure to compensate for interference of diquat in the determination of paraquat. The error for these methods is established to be within ±2 per cent.