Anodic stripping voltammetry of lead and cadmium using a mercury film electrode and thiocyanate Original Research Article

It is well known that lead and cadmium can be determined with good sensitivity using anodic stripping voltammetry (ASV) and a mercury film electrode. However, the mercury film formation is poorly reproducible and cannot fully be removed electrochemically. We have evaluated procedures to improve the reproducibility and sensitivity of the ASV method and found that in the presence of thiocyanate the film can be plated reproducibly and removed fully after each scan. Furthermore we optimised the analytical parameters pH, electrolyte composition, and deposition time and potential. Optimal analytical conditions were found to be a thiocyanate concentration of 5 mM, and a pH of 5.6. Optimisation of the deposition potential unexpectedly showed that the sensitivity was greatly improved by using a very negative potential of −1.5 V, causing a 10-fold increase in the sensitivity of cadmium, and a 3-fold increase for lead. In these conditions the limit of detection (3σ) was 5 pM cadmium and 8 pM lead (standard deviations of 1.7% and 2%) using a deposition time of 5 min. The method was successfully applied to the determination of cadmium and lead in lake waters and certified seawater after UV digestion.