Anodic stripping voltammetry with mercury electrodes in extracts of cadmium,lead, thallium and indium diethyldithiocarbamate complexes and analysis of mixtures

The selectivity of the determination of traces of cadmium, lead, thallium and indium is improved by direct coupling of liquid/liquid extraction and anodic stripping voltammetry. Metals are extracted from aqueous solution to benzene or chloroform after the addition of sodium or zinc diethyldithiocarbamate. Stripping voltammetry of Cd, Tl and Pb at a hanging mercury drop electrode or mercury film electrode is done in benzene/methanol medium (1:1) with 0.1 M NaClO₄ as supporting electrolyte. For indium, the medium is chloroform/ethanol/water (1:4:1) with 0.005 M sodium acetate/0.06 M KBr/0.06 M HCl as supporting electrolyte. The complexes in acidic solution can be decomposed by mercury (II) ions, which provides useful shifts of deposition potentials. Calibration graphs are linear at concentrations of about 10^?7 M with a detection limit of 1×10^?8 M. The method is applied to determine a single metal in the presence of a large amount (1000-fold) of interfering metal.