Determination of diquat at a Nafion film modified glassy carbon electrode using electrocatalytic voltammetry

A Nafion polymer film modified glassy carbon electrode (NFGCE) was used for the determination of diquat. Diquat was preconcentrated onto NFGCE by the cation-exchange feature of Nafion at open circuit potential and determined by cathodic differential pulse voltammetry (DPV) in a medium containing permanganate. Good sensitivity was achieved through the good cation-exchange property of Nafion and the catalytic process between diquat and permanganate. With 4 min accumulation, the analytical signal versus concentration dependence was linear from 3 x 10^-9 M (0.55 ppb) to 4 x 10^-7 M (73 ppb), and the detection limit was 0.21 ppb. The interferences from metal ions could be reduced by adding ethylenediaminetetraacetate (EDTA) into the sample solutions. The use of Nafion also improves the resistance to interferences from surfactants.