Voltammetric determination of traces of Cr(VI) in the presence of Cr(III) and humic acid Original Research Article

A sensitive and very selective procedure for voltammetric determination of traces of Cr(VI) in the presence of Cr(III) and humic acid is presented. The calibration graph is linear from 1×10−9 to 1×10−7 and from 2×10−10 to 2×10−8 mol l−1 for deposition times 60 and 300 s, respectively. The relative standard deviation for 1×10−8 mol l−1 Cr(VI) is 5.2 % (n=5). The detection limit estimated from 3σ for low concentration of Cr(VI) and the deposition time 300 s is 6×10−11 mol l−1. The detection limit estimated from 3σ of peak in the blank is 3×10−11 mol l−1. The influence of common foreign ions is also presented. The validation of the method was carried out by comparison of the results of determination of Cr(VI) in soil samples by the method proposed with those obtained by spectrophotometry.