Spectrophotometric determination of gold(iii) with p-dimethylaminobenzilidenerhodanine in hydrochloric acid-ethanol medium

The reaction between gold(III) and p-dimethylaminobenzilidenerhodanine in hydrochloric acid medium containing 20% v/v ethanol has been studied spectrophotometrically. It has been established that the process is very complicated: gold(III) is reduced to gold(I) which reacts with unchanged reagent. The value of the equilibrium constant is 2.56 +/- 0.45. Conditions are proposed for the determination of 2-8 mug of gold in 25 ml, with a standard deviation of 0.04 mug 25 ml .