Abstract

An adsorptive stripping voltammetric (AdSV) method for the direct determination of Co in the presence of Ni and Zn in natural waters based on metal complexation with pyrogallol red (PR) and subsequent adsorptive deposition onto a hanging mercury drop electrode (HMDE) is presented. Optimal analytical conditions were found to be: pH 7.8 (HEPES buffer 0.05 mol L -1); C PR = 2.0 ?mol L -1; E ads = -0.40 V vs. Ag/AgCl; and t ads = 60 s. Peak current is proportional to Co concentration over the 0.0-40.0 ?g L -1 range, with a 3? detection limit of 0.02 ?g L -1. The relative standard deviation for a Co solution (5.0 ?g L -1) was 2.1% for six successive assays. The Ni-PR complex is reduced at -0.86 V, free ligand at -0.97 V, and the Co-PR complex at -1.08 V. In the presence of tetrabutylammonium tetrafluoroborate (TBATFB) the Ni-PR complex is reduced at 180 mV more positive potentials and the signal is finer. However, Zn interferes with the determination of Co due to overlapping of the waves. In the presence of 8-hydroxyquinoline (Ox) the Zn-Ox complex is reduced at 130 mV more negative potentials than the Co-PR complex. The method was validated by determining Co in spiked synthetic sea water (ASTM D665), certified reference water (TMDA-61) and was applied to the determination of Co in sea water, tap water, and mineral water samples after UV digestion. © 2012 by ESG.