Determination of Cr(VI) in the presence of complexing agents and humic substances by catalytic stripping voltammetry

The voltammetric method of Cr(VI) determination in a flow system is proposed. Determinations can be carried out in the simultaneous presence of an excess of Cr(III), complexing agents, humic substances and surfactants. The method is based on the combination of a selective accumulation of the product of Cr(VI) reduction to the metallic state and a very sensitive voltammetric method of chromium determination in the presence of DTPA and nitrates. The calibration graph is linear from 1 x 10(-9) to 5 x 10(-8) mol L-1 for accumulation time of 30 s. The relative standard deviation is 5.2% (n = 5) for Cr(VI) concentration 1 x 10(-8) mol L-1. The influence of humic and fulvic acids, complexing agents and surfactants on Cr(VI) and the interfering Cr(III) signal is presented. The method was applied to Cr(VI) determination in certified reference material, soil sample, natural water sample and EDTA extracts from soil certified reference material.