Sequential determination of five heavy metal ions in Brazilian phosphate fertilizers and surface waters by stripping voltammetry

A method comprised of multi-detection steps for the sequential determination of uranium, cadmium, lead, thallium, and silver, using electroanalytical tools, is proposed herein. Firstly, adsorptive stripping voltammetry was applied to assay the U(VI)–cupferron complex in the differential pulse mode. In sequence, using the same aliquot of the sample, the quantifications of cadmium and lead were performed simultaneously by differential pulse anodic stripping voltammetry with the environmentally friendly bismuth film electrode. Due to the overlapping peaks of cadmium and thallium, the addition of EDTA enabled the determination of thallium by anodic stripping voltammetry. On employing the ex situ bismuth-film-modified electrode, the current intensity increased for the four heavy metal ions. After the removal of the bismuth film, silver was quantified at a glassy carbon electrode by anodic stripping voltammetry, as the last step of the multi-detection method. The method was successfully applied to phosphate fertilizer samples after open-vessel wet decomposition (HNO3/H2O2). Uranium was detected in the range of 36.2–144.0 mg kg−1. Cadmium and lead were detected in concentrations of up to 41.4 and 204.0 mg kg−1, respectively. The concentrations of thallium and silver were below the detection limits. Surface water samples (river water and lagoon water) were also analyzed with respect to the heavy metal ions. Validation was performed using the standard reference materials SRM-695 (phosphate fertilizer) and SRM-1643e (water).