EFFECT OF THE DEPOSITION POTENTIAL ON THE VOLTAMMETRIC DETERMINATION OF COMPLEXING LIGAND CONCENTRATIONS IN SEA-WATER

The effect of the deposition potential on the determination of complexing ligand concentrations in natural waters was investigated by titration with Cu from sea-water samples originating from the North Sea and monitoring the labile Cu concentration after deposition at two potentials, viz., -0.05 and -0.7 V. The amount of deposited metal was measured by cathodic stripping voltammetry with ligand competition, using tropolone as the added ligand. It was found that the complexing ligand concentration detected decreased by more than 60% when the more negative deposition potential was applied. The data indicate that a significant fraction of the organic complexes of Cu in natural waters is electrochemically labile at negative deposition potentials and is not determined by anodic stripping voltammetry. The concentrations and conditional stability constants of the complexing ligands in the North Sea are similar to those detected previously in the Irish Sea.