Voltammetric determination of the complexation parameters of zinc in marine and estuarine waters

Abstract

Anodic stripping voltammetry (ASV) at the rotating disk electrode was used to probe the zinc-organic ligands interactions in Narragansett Bay Water samples and in samples collected in the Slope Water region off the U.S. mid-Atlantic Bight. In Narragansett Bay Water, two distinct groups of complexing ligands were detected, which have conditional stability constants (log K) of 7.7 and 7.0 and represent solution and surface complexation respectively. In samples collected near the western edge of the Gulf Stream two classes of dissolved organic ligands could be distinguished, with average stability constants (log K 1, log K 2) of 9.3 and 7.6. Because of the complexity of the systems studied, the complexation properties of these ligands had to be measured over a range of pH values and/or a range of electrode rotation rates, to obtain correct and precise estimates of their stability constants. This type of approach gave a complex but coherent interpretation of all the ASV data (i.e. variation of the ASV signal with zinc concentration, pH and electrode rotation rate), and is to be particularly recommended to workers confronted with new or complex marine systems.