Determination of diquat by a photokinetic method

Abstract

A rapid and sensitive photokinetic method for the determination of diquat (DQ²⁺) is described, based on the rate of photoreduction of DQ²⁺ by ethylenediaminetetraacetic acid sensitised by Acridine Yellow in the absence of oxygen. The rate of photoreduction is a linear function of the concentration of DQ²⁺ at very low concentration. The rate of this photochemical reaction was monitored polarographically by recording the limiting current of p-benzoquinone, which is reduced by the radical monocation DQ^+· that is generated in the photochemical reaction. The results obtained by the application of the fixed-time, fixed-concentration and initial-rate kinetic methods were evaluated. An alternative method for monitoring the rate of the process is by measuring the time necessary for the total reduction of p-benzoquinone. The end-point is detected with two platinum electrodes at an applied voltage of 100 mV. The procedure was applied successfully to the determination of diquat in commercial herbicides, waters, soils, potatoes and blood serum.