Differential-pulse voltammetric determination of low μg l−1 cyanide levels using EDTA, Cu(II) and a hanging mercury drop electrode Original Research Article

The proposed method for cyanide determination at the ultratrace level by differential pulse voltammetry is based in the sensitivity enhancement obtained when both Cu(II) and EDTA are present in the background electrolyte. Comparison of the detection limits and linear dynamic ranges using the conventional borate (pH 9.75), and the proposed borate-EDTA–Cu(II) background electrolytes was carried out. Best results have been obtained with the addition of 0.5 mmol l−1 EDTA and 0.02 mmol l−1 of Cu(II), which allow a detection limit of 1.7 μg l−1 CN− (65 nmol l−1 — absolute detection limit 34 ng) with a precision better than ±2% for a 40 μg l−1 level. Calibration range extended from detection limit up to 100 μg l−1. Cyclic voltammetry indicates that the measured cyanide peak is obtained when the electrogenerated CuCN adsorbed onto the hanging mercury drop electrode surface, is oxidised at positive going potential scan. The method has been successfully applied to various industrial waste waters such as metal-finishing waste waters, water/sand mixtures from cleaning processes of coke production, leachates from wastes obtained from electrolytic cells of aluminium production, and liquors from gold extraction industry. Results obtained by the proposed method showed good agreement with those obtained by the standard methods (ion-selective potentiometry and the spectrophotometric pyridine method).