Simultaneous determination of copper, cadmium and nickel by ratio derivative polarography

Ternary mixtures of metals can be resolved by using the ratio derivative polarography without the need for any pre-separation step. The method is based on the simultaneous use of the first derivative of ratios of polarograms and measurements of zero-crossing potentials. The polarogram of the mixture is obtained and the amplitudes of the current at appropriate potentials are divided by the corresponding amplitudes in the polarogram of a standard solution of one of the components, and the subsequent derivation against potential results to the first derivative of the ratio polarogram. The concentrations of the other two components are then determined from their respective calibration graphs established by measuring the ratio derivative analytical signal at the selected zero-crossing points. The method has been successfully applied for resolving ternary mixtures of copper, cadmium and nickel, which have overlapped polarograms in pH 2.87 Britton-Robinson buffer. The concentration ranges to be determined are 0.30-1.40 mg l(-1) for copper, 0.90-4.50 mg l(-1) for cadmium and 0.20-1.20 mg l(-1) for nickel, and the recoveries are 88.3-101.9% for copper, 92.2-105.4% for cadmium and 95.0-107.0% for nickel.