Ultrasensitive hexavalent chromium determination at bismuth film electrode prepared with mediator.

A bismuth film electrode prepared in situ with a reversibly deposited mediator (Zn) applied for ultrasensitive determination of Cr(VI) using differential pulse catalytic adsorptive stripping voltammetry is presented. The optimization of experimental conditions such as composition of the supporting electrolyte, potential and time of bismuth film formation as well as analyte accumulation, and DP mode parameters is reported. For 180 s accumulation time, very low limits of detection and quantification of Cr(VI) were obtained, with 5.8 × 10-14 and 1.9 × 10-13 mol L-1, respectively. The relative standard deviation for 5.0 × 10-13 mol L-1 of Cr(VI) was 3.9% (n = 5). Finally, the proposed procedure was applied to determine Cr(VI) in the certified reference materials - NASS-6 (seawater), SLEW-3 (estuarine water) and TMRAIN-04 (rainwater) - as well as in river water samples. Furthermore, the obtained results show that the proposed voltammetric procedure employing the bismuth film electrode prepared with mediator appears to form a very promising tool for the speciation of chromium at ultratrace level.