Spectrophotometric determination of total cyanide, iron-cyanide complexes, free cyanide and thiocyanate in water by a continuous-flow system

Abstract

A combination of three automated methods has been developed to determine total cyanide, free cyanide [i.e., HCN(aq)+ CN^–], iron-cyanide complexes and thiocyanate. The methods are based on a continuous-flow technique, combined with spectrophotometric detection, and have a detection limit of 0.6 µg l^–1. The distinction between iron-cyanide complexes and free cyanide plus thiocyanate was made by UV irradiation and distillation with citric acid. The distinction between free cyanide and thiocyanate was made by masking free cyanide with formaldehyde. Rapid and complete recovery of iron-cyanide complexes was obtained; the interference from nitrate was minimised. Shielding the samples from diffuse daylight appeared to be necessary to prevent rapid photolysis of the iron-cyanide complexes.