Rapid determination of copper, lead and cadmium in unpurged seawater by adsorptive stripping voltammetry

Abstract

A rapid method to determine copper, cadmium and lead directly in seawater is presented. The procedure uses adsorptive cathodic stripping voltammetry and rapid (> 1 V s−1) potential scans. The ligand concentration, pH, deposition potentials and electrochemical variables are optimised for these conditions. The method is especially insensitive to the turbulence of the solution during the scan. No perturbations are produced by stirring during the scan. Oxygen interference is also drastically decreased since adsorbed metal peaks are favoured at high scan speeds. This interference together with capacitative components are eliminated by blank subtraction. The blank is measured under the same conditions, but without collection. A procedure to avoid the overlapping, especially between copper and lead peaks, is also worked out. This uses subtraction of repetitive scans in which some of the metal peaks are removed. The replicate scans are made in the same drop after the first scan, using a combination of times and reoxidation potentials. This procedure successfully results in resolving overlapping peaks without introducing delays or losses of sensitivity. The reproducibility and accuracy of the method were calculated by reference to open oceanic waters. Applications of the method to the determination of copper, lead and cadmium in an oceanic profile (Central Atlantic Ocean) is given.