Simultaneous determination of several trace metals in seawater using cathodic stripping voltammetry with mixed ligands

Cathodic stripping voltammetry (CSV) is normally restricted to the determination of one or two elements simultaneously due to the specificity of the ligand. By using a mixture of ligands we have attempted to enable the simultaneous determination of several elements (Cu, Pb, Cd, Ni, Co and Zn) in seawater. Scans containing six resolved peaks corresponding to these metals were obtained using a combination of DMG (dimethylglyoxime) and oxine (8-hydroxyquinoline) in seawater. These metals can be quantified at concentrations above 0.3 nM Cu, 0.2 nM Pb, 0.l nM Cd, 0.4 nM Ni, 0.6 nM Zn and 0.02 nM Co. The sensitivity for Co and Zn is not sufficient for their determination in unpolluted waters. Several procedures were developed to determine various combinations of metals at lower concentrations, and optimised by making use of different ligand combinations, resulting in higher sensitivities. Nitrite was used to improve the sensitivity for Co using a catalytic reaction. The metals were found not to interfere with each other when present at concentrations normally encountered in seawater. Suitable linear ranges of voltammetric response were identified. The limits of detection using the optimised mixed ligand solutions are similar to those for the ligands separately. The major improvement is the possibility of simultaneous determination of several metals in a sample within a few minutes and the applicability to ship-board automated determinations.