Spectrophotometric determination of dissolved oxygen in water through the formation of an argentocyanide complex with silver sol

Abstract

A simple and sensitive method for the determination of dissolved oxygen (DO) in water has been developed, involving the dissolution of a gelatin-stabilished yellow silver sol formed with cyanide ion in the presence of oxygen. The coloured sol becomes colourless argentocyanide ion at the end-point. The reagent solution is fairly stable over the experimental time scale and the change in absorbance at a wavelength of 415 nm gives a measure of the concentration of dissolved oxygen 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 and is free from interferences. It has the advantage of being capable of determining oxygen down to a concentration of 50 p.p.b. in water samples. The slope of the calibration graph is 0.206 A ml µg^–1[absorbance units per (microgram per millilitre)]. The molar absorptivity of the solution is 6.58 × 10³ l mol^–1 cm^–1 with a relative standard deviation of 0.9%, a confidence limit (for 10 determinations) of 0.17 ± 0.001 p.p.m. and a Sandell sensitivity of 1.63 × 10^–2µg cm^–2.