Abstract
Redox speciation of chromium has attracted a great deal of interest in view of the toxic properties of Cr(VI) compared with the much less toxic Cr(III). Cr(VI) dominates in effluents from metallurgical and metal finishing industries and Cr(III) exists mainly in tannery, textile and decorative plating industry wastes. The total chromium concentration in unpolluted natural waters is 1-10 ^g L-1 1. A procedure for the determination of chromium in contaminated waters by AdSV using morin or morin-5-sulfonic acid as adsorbing and complexing agents have been optimized. Cr(VI)-morin complexes are adsorbed into electrode and then reduced to Cr(III)-morin complexes. In the presence of tetrabutylammonium tetrafluoroborate peak current of free ligand decreases and the peak current of complex were lightly enhanced. The variation of peak current with pH, adsorption time, adsorption potential, ligand and quaternary ammonium salt concentration, and some instrumental parameters such as stirring rate in the accumulation stage and step amplitude, pulse amplitude and step duration in the obtaining of the square wave voltamperograms were optimized. The best experimental parameters were pH = 4.0 - 8.0 (Britton Robinson buffers), Cmomi = 3.5 |imol L-1, CTBATFB = 10.0 |i mol L-1, tads = 60 s and Eads = -0.50 V vs Ag/AgCl. Under these conditions the peak current was proportional to the chromium concentration over the 0.0-25.0 |ig L-1 range, with a detection limit of 0.7 |ig L-1. Reproducibility for 6.0 |ig L-1 chromium solution was 3.1 % (n = 6). The method was validated with synthetic sea water spiked with 22 metal ions and fortified water GBW08607 (Reference material. Certified value: Cr 0.500|ig/g) and applied to analysis of Cr(VI) in the presence of Cr(III) in contaminated waters.