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

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 1x10(-9) to 1x10(-7) and from 2x10(-10) to 2x10(-8) mol l(-1) for deposition times 60 and 300 s, respectively. The relative standard deviation for 1x10(-8) mol l(-1) Cr(VI) is 5.2% (n=5). The detection limit estimated from 3 sigma for low concentration of Cr(VI) and the deposition time 300 s is 6x10(-11) mol l(-1). The detection limit estimated from 3 sigma of peak in the blank is 3x10(-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. (C) 2000 Elsevier Science B.V. All rights reserved.