Spectrophotometric Determination of Co~(2+) in Nickel-Cobalt Alloy Electroplating Bath with Fading Reaction of Thionine

It is investigated that Co~(2+)can catalyze the fading oxidation of thionine by NaBiO_(3) in HCl medium at 100℃.The maximum absorption wavelength is 600 nm and the apparent molar absorptivity is 3.494×10~(4)L/(mol·cm)~(-1).The linear range is 0—50μg/mL of Co~(2+).The detection limit for Co~(2+)is 0.05205 μg/mL.The method has been applied to the determination of Co~(2+)in nickel-cobalt alloy electroplating bath with satisfactory results.