Catalytic Kinetic Photometric Determination of Trace Amount of Iridium(Ⅲ) by the Reaction System of Brilliant Green and Hydrogen Peroxide

In 0.01 mol·L-1 H2SO4 medium and heated in a water bath at 95 ℃ for 10 min, the oxidative color-fading reaction of brilliant green with H2O2 was remarkably catalyzed by the presence of trace amount of Ir(Ⅲ). Based on these facts, a catalytic kinetic photometric method for determination of trace amount of Ir(Ⅲ) was proposed. It was proved that the catalytic process was a first order reaction for Ir(Ⅲ) and a pseudo first order reaction for total reaction. Values of apparent rate constant and apparent activation energy were found to be 7.383×10-4s-1 and 65.27 kJ·mol-1 respectively. Linear relationship between the values of decrease in absorbance (ΔA) and mass concentration of Ir(Ⅲ) was obtained in the range within 0.06 mg·L-1. Detection limit (3s/k) of the reaction found was 1.152×10-7g·L-1. In analyzing samples of molecular sieve and activated carbon by this method for Ir(Ⅲ) contents, giving recovery in the range of 97%-104%.