Differential-pulse voltammetric determination of low mu gl(-1) cyanide levels using EDTA, Cu(II) and a hanging mercury drop electrode

The proposed method for cyanide determination at the ultratrace level by di fferential pulse voltammetry is based in the sensitivity enhancement obtain ed when both Cu(II) and EDTA are present in the background electrolyte. Com parison of the detection limits and linear dynamic ranges using the convent ional berate (pH 9.75), and the proposed borate-EDTA-Cu(II) background elec trolytes 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 detect ion limit of 1.7 mu g l(-1) CN- (65 nmol l(-1) - absolute detection limit 3 4 ng) with a precision better than +/-2% for a 40 mu g l(-1) level. Calibra tion range extended from detection limit up to 100 mu g l(-1). Cyclic volta mmetry indicates that the measured cyanide peak is obtained when the electr ogenerated CuCN adsorbed onto the hanging mercury drop electrode surface, i s oxidised at positive going potential scan. The method has been successful ly applied to various industrial waste waters such as metal-finishing waste waters, water/sand mixtures from cleaning processes of coke production, le achates from wastes obtained from electrolytic cells of aluminium productio n, and liquors from gold extraction industry. Results obtained by the propo sed method showed good agreement with those obtained by the standard method s lion-selective potentiometry and the spectrophotometric pyridine method). (C) 2000 Elsevier Science B.V. All rights reserved.