Differential pulse anodic stripping voltammetric determination of Cd and Pb at a bismuth glassy carbon electrode modified with Nafion, poly(2,5-dimercapto-1,3,4-thiadiazole) and multiwalled carbon nanotubes

Differential pulse anodic stripping voltammetry was applied to detect Pb2+ and Cd2+ at a glassy carbon electrode modified with Nafion, poly(2,5-dimercapto-1,3,4-thiadiazole) (PDMcT), and multiwalled carbon nanotubes (MWCNTs). Preconcentration was accomplished at −1.0 V vs. SCE in pH 5 buffer containing 400 μg L−1 Bi3+ for 6 min and resulted in high sensitivity, selectivity and reproducibility. Electrochemical quartz crystal microbalance studies revealed that PDMcT is cleaved under the reductive conditions to form thiol groups that bind Pb2+ and Cd2+ ions, whilst the Nafion binder stabilizes the film and the MWCNTs improve electroactivity. The presence of the bismuth film improves sensitivity and reproducibility. Under optimum conditions, the electrode responds linearly to Cd2+ ions in the concentration range from 0.05 to 20 μg L−1, and to Pb2+ from 0.1 to 22 μg L−1. The limits of detection (S/N = 3) are 0.03 and 0.05 μg L−1, respectively. This method was successfully applied to the determination of the two ions in water samples.