Determination of Cobalt in Tin-Cobalt-Zinc Alloy Plating Bath by Catalytic Dynamic Spectrophotometric Method

A new determination method of Co~(2+) was built according to the oxidation fading reaction of sodium bismuthate and thionine catalyzed by Co~(2+) in boiling hydrochloride solution.Beer' law was obeyed as Co~(2+) concentration is in the region of 0~50 μg/mL,the apparent molar absorptivity is 3.494×10~4(L·mol/cm),and the detection limit is 0.052 05 μg/mL.The method can be used in concentration determination of Co~(2+) in Sn-Co-Zn alloy plating bath with satisfactory result.