Spetrophotometric determination of trace Co~(2+) in acidic gold electroplating bath with fading reaction of methyl violet

Co~(2+) can catalyze discoloring oxidation of methyl violet by hydrogen peroxide in media of nitric acid at constant temperature of 95 ℃ with water bath. Thereby method of fading spectrophotometric determination of trace Co~(2+) was presented. The maximum absorptivity wavelength is 580 nm and the apparent molar absorptivity is 8.69×10~5 L/mol·cm. (The linear) range of the determination was 0～135 μg/L and detection limit was 2.53×10~(-10) μg/L. The method was applied to determine Co~(2+) in acidic gold electroplating bath with satisfactory results.