Electrochemical Behavior of Paraquat at Graphene Oxide Modified Glassy Carbon Electrode and Its DPV Determination

The graphene oxide modified glassy carbon electrode was prepared by dropping 10 μL of graphene oxide suspension (1 g·L^-1) onto the surface of glassy carbon electrode, drying, and reduction at -0.9 V for 600 s in 0.1 mol·L^-1 KH₂PO₄ solution. The modified electrode was characterized by scanning electron microscopy, transmission electron microscopy and electrochemical method. The electrochemical behavior of paraquat at graphene oxide modified electrode was studied by differential pulse voltammetry. It was found that, in a base solution of PBS (pH 7.5) the modified electrode showed obvious electrocatalytic effect on the reduction of paraquat. As shown in the differential pulse voltammogram, 2 reduction peaks (at -0.6, -0.1 V) were observed, with the latter overlapped with the reduction peak of the base solution. The reduction peak at -0.6 V and its peak current (i_pc) were taken in the following measurement. As shown by the experimental results, the optimum potential found for enrichment of paraquat at the modified electrode was -0.6 V with a time of 200 s and a scanning rate of 50 mV·s^-1. Under optimal conditions, linear relationships were found between reduction peak current at -0.6 V and concentration of paraquat in the ranges of 9.00×10^-7-1.00×10^-5mol·L^-1, and 1.00×10^-5-5.00×10^-5mol·L^-1, with detection limit (3s/k) of 1.64×10^-7mol·L^-1. The method was applied to determination of paraquat content in pesticides, and the determined value was in consistency with the marked value. Test for recovery was made by standard addition method to soil sample, giving results in the range of 89.5%-114%.