Spectrophotometric determination of Co~(2+) in tin-cobalt alloy electroplating bath with fading reaction of ponceau S

Co~(2+) ion can catalyze discoloring oxidation of ponceau S by sodium bismuthate at a constant temperature of 90 ℃ with water bath.Thereby a new method of fading spectrophotometric determination of Co~(2+) was presented.The maximum absorptivity wavelength is 520 nm and the apparent molar absorptivity is 1.814×103 L/(mol·cm).The linear range of the determination is 0～50 μg/mL and detection limit is 0.538 μg/mL.The method was applied to determine Co~(2+) in gun-black tin-cobalt alloy electroplating bath with satisfactory results.