Determination of selenium by catalytic cathodic stripping voltammetry

Abstract

A procedure is described for the determination of selenium in natural waters using cathodic stripping voltammetry in the presence of rhodium. Advantage is taken from a catalytic effect on the electrochemical reduction of protons in the presence of a mixed complex of selenide with rhodium and chloride, containing Cl–Rh–SeH species. The catalysis causes a very large peak-current at a negative peak potential for low (picomolar) selenium concentrations, close to the hydrogen wave. In addition to the selenium concentration, the peak height depends on the concentrations of acid (H +) and chloride, and suffers from strong interference by organic surfactants. Optimised conditions include 0.3 M HCl, 75 ppb Rh(III) and a deposition potential of −0.2 V. UV-digestion was used to eliminate the interference caused by organic material and to convert Se(VI) to Se(IV). A 3 σ detection limit of 2.4 pM Se(IV) was calculated from the standard deviation of a low selenium concentration (17 pM) using a deposition time of 50 s.