A comparison of boron-doped diamond thin-film and Hg-coated glassy carbon electrodes for anodic stripping voltammetric determination of heavy metal ions in aqueous media

The performance of boron-doped diamond (BDD) for the anodic stripping voltammetric (ASV) determination of heavy metal ions (Zn2+, Cd2+, Pb2+, Cu2+, Ag+) was compared with that of Hg-coated glassy carbon (Hg-GC). Hg has historically been the electrode of choice for ASV but there is an ongoing search for alternate electrodes and diamond is one of these. Despite the fundamentally different nature of the metal reduction and oxidation reactions on these two electrodes, BDD provides as good or superior analytical detection figures of merit when compared to Hg. The stripping peak potentials for all the metals studied were similar at both electrodes indicating that BDD is as active as Hg for metal phase formation and oxidation. Due to the more heterogeneous chemical and electrical properties across the BDD surface, the stripping peaks were broader and more asymmetric than they were for Hg-GC. The linear dynamic range for BDD was three to four orders of magnitude (r2 > 0.995), similar to Hg-GC, but the sensitivity for BDD was three to five times lower. However, the lower background current and noise for BDD enabled detection limits as low as those seen for Hg-GC. The minimum concentration of each metal ion detectable (S/N ≥ 3) with BDD was in the mid to low ppb range (e.g., 50 ppb Zn2+, 1.0 ppb Cd2+, 5.0 ppb Pb2+, 10 ppb Cu2+ and 1.0 ppb Ag+). BDD exhibited an electrode-to-electrode and run-to-run variability of less than 5%, which is comparable to that for Hg-GC. The possibility of incomplete metal oxidation and metal phase detachment from BDD was investigated using double step chronoamperometry. Neither of these processes was found to occur to any appreciable extent. The results demonstrate that BDD is a viable alternate electrode to Hg for ASV.