Spectrophotometric determination of dissolved oxygen in water by the formation of a dicyanoaurate(I) complex with gold sol

Abstract

A simple and sensitive spectrophotometric method for the determination of dissolved oxygen (DO) in water has been developed involving the dissolution of a gelatin-stabilized gold sol formed with cyanide ion in the presence of oxygen. The coloured sol is converted into the colourless dicyanoaurate(I) ion at the end-point. The reagent solution is fairly stable over the experimental time scale and the change in absorbance at 540 nm gives a measure of the concentration of DO in water. The effects of foreign ions on the determination indicated that the method is suitable for determining DO in both drinking and effluent waters. It has the advantage of being capable of determining DO down to a concentration of 60 ppb in water samples. The slope of the calibration graph is 0.16 A ml µg^–1. The molar absorptivity of the solution is 5.12 × 10³ dm³ mol^–1 cm^–1 with a relative standard deviation of 0.85%; the confidence limit (95%) for 0.20 ppm of DO (ten replicates) is 0.20 ± 0.002 ppm.