Determination of ultra-trace amounts of cadmium in natural waters by the combination of a solvent extraction procedure and anodic stripping voltammetry

Abstract

A method combining a solvent extraction procedure with anodic stripping voltammetry for the reliable determination of ultra-trace amounts of cadmium in natural waters is reported. The element is pre-concentrated as cadmium dithiocarbamate into Freon and subsequently back-extracted into an acidic aqueous medium for the voltammetric determination. The utilisation of the pre-concentration procedure prior to the determination substantially reduces the required plating time for the electrochemical technique and hence permits a considerable reduction in the over-all analysis time. The separation of the analyte from the bulk of the natural water matrix permits the direct determination of 0.1 µg l^–1 of the element from a calibration graph, whereas for lower concentrations the use of the standard additions method is necessary for reliable determination. The minimum amount of cadmium that can be pre-concentrated and determined reliably by the voltammetric technique is 0.025 µg l^–1. The application of the over-all approach to an NBS Standard Reference Water (fresh water) and local sea water samples was successful.