Copper complexing capacities of freshwaters by adsorptive cathodic stripping voltammetry Original Research Article

Copper complexation in freshwater was investigated by cathodic stripping voltammetry (CSV) with ligand competition using 8-hydroxyquinoline (oxine). Complexing capacity titrations were used to determine concentrations of natural copper complexing ligands and their conditional stability constants. The effect of the adsorption potential on the determination of copper complexation was studied at three potentials of −0.15, −0.7 and −1.1 V. It was found that the detected complexing ligand concentrations decreased from 6.7 to 69.4% when the potential used was more negative than −0.15 V. The decrease was greater at more negative potentials and lower detection windows. Detailed measurements of copper complexation in freshwater were carried out at three detection windows by varying the oxine concentrations from 7.3 to 36.7 μM and confirmed the presence of several complexing ligands. The detected complexing ligand concentrations were found to decrease with increasing detection window, whereas the conditional stability constants were found to increase. These findings confirm that a spectrum of natural complexing ligands exist in freshwater with weaker ligands being determined at lower detection windows and stronger ligands being determined at higher detection windows. A good linear relation was found between log αCuLx and log αCuox.