Determination of cobalt based on its catalytic effect on the decomposition-reaction of Amide Black 10B with hydrogen peroxide

Abstract

Color-fading of Amide Black 10B (AB10) based on the catalytic reaction of Co and Cu has been applied to the determination of Co. The decomposition reaction of AB10 with hydrogen peroxide was catalyzed by cobalt and copper in alkaline medium. Tiron accelerated the catalytic reaction of cobalt, however, the effect of the activator was not significant for copper. The recommended procedure is as follows: Take a sample solution containing from 0.25 to 1.5 μg Co(II), adjust the concentration of hydrogen peroxide to 0.25%, AB10 to 5×10^-5 M, and Tiron to 6×10^-3 M in the final solution (50 ml). When stable absorbance (at 600 nm) is obtained for the circulating sample solution, add 2 ml of 2 M sodium hydroxide solution. A calibration curve was made between ln(A₁/A₆) and the concentration of cobalt or copper, where A₁ and A₆, were the absorbances of AB 10 at 1 min and 6 min, respectively. The values of ln(A₁/A₆) were nearly proportional to 30 ppb of Co and to 40 ppb of Cu. The R.S.D. was 2.5% (n=6) at 30 ppb of Co(II), but the R.S.D. of copper determination was 17% under the same conditions. Among diverse ions, 300-fold V, 30-fold Zn and 3-fold Fe relative to Co interfered with the determination of cobalt. The proposed method was successfully applied to the determination of cobalt (0.020.3%) contained in nickel chemical reagents.