Determination of paraquat in biological and environmental samples by a photokinetic method

A fast and sensitive photokinetic method for the determination of paraquat (MV²⁺) (1?27×10^?5M) is described, based on the rate of photoreduction of MV²⁺ by EDTA, sensitized by acridine yellow in the absence of oxygen. The rate of photoreduction, which is a linear function of the concentration of MV²⁺ is monitored polarographically by recording the limiting current of p- benzoquinone, which is reduced by the radical monocation MV^+· generated in the photochemical reaction. The results obtained by the application of the fixed-time, fixed-concentration change and initial-rate kinetic methods are 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 has been successfully applied to the determination of paraquat in commercial herbicides, waters, and flowers and in spiked soils and blood sera.