A novel spectrophotometric method for determination of cyanide using cobalt (II) phthalocyanine tetracarboxylate as a chromogen

Abstract

Cobalt (II) phthalocyanine tetracarboxylate [Co (II)Pc-COOH] has been prepared and used in aqueous solutions as a novel chromogenic reagent for the spectrophotometric determination of cyanide ion. The method is based on measuring the increase in the intensity of the monomer peak in the reagent absorbance at 682 nm due to the formation of a 1 : 2 [Co (II)Pc-COOH] : [CN] complex. The complex exhibits a molar absorptivity (ε) of 7.7 × 104 L mol−1 cm−1 and a formation constant (Kf ) of 5.4 ± 0.01 × 106 at 25 ± 0.1°C. Beer's law is obeyed over the concentration range 0.15–15 µg mL−1 (5.8 × 10−6–5.8 × 10−4 M) of cyanide ion, the detection limit is 20 ng mL−1 (7.7 × 10−7 M) the relative standard deviation is ±0.7% (n = 6) and the method accuracy is 98.6 ± 0.9%. Interference by most common ions is negligible, except that by sulphite. The proposed method is used for determining cyanide concentration in gold, silver and chromium electroplating wastewater bath solutions after a prior distillation with 1 : 1 H2SO4 and collection of the volatile cyanide in 1 M NaOH solution containing lead carbonate as recommended by ASTM, USEPA, ISO and APAHE separation procedures. The results agree fairly well with potentiometric data obtained using the solid state cyanide ion selective electrode.