1999 Volume 48 Issue 7 Pages 659-667
The catalytic kinetic determination of cobalt(II) with Eriochrome Black T (EBT) in the presence of hydrogen peroxide was investigated. Co(II) was determined by the reaction rate constant obtained from the decomposition of EBT with the hydroxyl radical due to the catalytic reaction of Co (II) in the presence of hydorogen peroxide. The change in the concentration of EBT was measured by a spectrophotometer. The effect of the concentration of EBT as an indicator reagent was greater than that estimated on the basis of the decomposition reaction with respect to the reaction rate constant. The cause of this phenomenon was the formation of an inert complex { Co(II) : EBT = 1 : 2}, which suppressed the formation of the hydroxyl radical produced in the presence of hydrogen peroxide and Co(II). A high sensitivity on the determination of Co(II) was obtained owing to the low concentration of EBT, because of the suppression of the inert complex formation. Therefore, indicator concentration used for the determination of Co(II) was decreased to be as low as possible by using a 5 cm cell. Farthermore, the effect of the addition of calcium(II) was examined in order to decrease the effective concentration of EBT. As a result, the addition of calcium ion increased the sensitivity of Co(II) determination as a ligand buffer reagent.
