Adsorptive stripping voltammetry of uranium: elimination of interferences from surface active substances and application to the determination in natural water samples

We report a simple and sensitive stripping voltammetric procedure for determination of trace quantity of U(VI) in environmental water samples containing high concentrations of surfactants. The procedure is based on the adsorptive accumulation of the U(VI)-cupferron complex onto a hanging mercury drop electrode, followed by a reduction of the adsorbed species by a voltammetric scan using differential pulse modulation. The interference from surfactants was eliminated by adsorption of interferents onto an Amberlite XAD-7 or XAD-16 resin. Optimum conditions for removing the surfactants by mixing the analysed sample with resin and for voltammetric measurements of uranium quantification were evaluated. Under optimal conditions the linear calibration plot for U(VI) was achieved in the simultaneous presence of 5.0 mg L-1 anionic, 2.0 mg L-1 cationic and 5.0 mg L-1 nonionic surfactants for an accumulation time of 30 s in the range 5.0 x 10(-10) to 2.0 x 10(-8) mol L-1, and the detection limit for the accumulation time of 30 s was about 1.4 x 10(-10) mol L-1. The proposed method was successfully validated using certified reference materials, seawater NASS-5 and rainwater TMRAIN-95.