Use of a modified, high-sensitivity, anodic stripping voltammetry method for determination of zinc speciation in the North Atlantic Ocean Original Research Article

Zinc speciation is considered to be an important determinant of the biological availability of zinc. Yet in oceanic surface waters, characterization of zinc speciation is difficult due to the low concentrations of this essential micronutrient. In this study, an anodic stripping voltammetry method previously developed for the total determination of cadmium and lead was successfully adapted to the measurement of zinc speciation. The method differs from previous zinc speciation anodic stripping voltammetry methods in that a fresh mercury film is plated with each sample aliquot. The fresh film anodic stripping voltammetry method was compared to competitive ligand exchange cathodic stripping voltammetry in a profile from the North Atlantic Ocean. Results using the fresh film anodic stripping voltammetry method were similar to those determined using the cathodic stripping voltammetry method, though ligand concentrations determined by fresh film anodic stripping voltammetry were generally slightly higher than those determined by cathodic stripping voltammetry. There did not seem to be a systematic difference between methods for the estimates of conditional stability constants. The ligand concentration in the North Atlantic profile ranged from 0.9 to 1.5 nmol L−1 as determined by fresh film anodic stripping voltammetry and 0.6 to 1.3 nmol L−1 as determined by cathodic stripping voltammetry. The conditional stability constants determined by fresh film anodic stripping voltammetry were 109.8–1010.5 and by cathodic stripping voltammetry were 109.8–1011.3.