Spectrophotometric determination of aqueous cyanide using a revised phenolphthalin method

This paper focuses on a revision of the phenolphthalin method for cyanide analysis, with the intent of producing a robust and sensitive spectrophotometric method. Limitations of the phenolphthalin chemistry were overcome by the addition of EDTA to the reagent. The revised reagent was found to have suitably fast kinetics, a linear dynamic range of 0.01–3.0 ppm cyanide, and a detection limit of 5 ppb. The method was tested for interferences and applied to the determination of cyanide in environmental waters.