Catalytic spectrophotometric determination of trace iridium(IV) using iridium(IV)-KIO4-chlorophosphonazo-mA system

A new catalytic spectrophotometric method was developed for the determination of Ir(IV) based on its catalytic effect on the oxidation reaction of chlorophosphonazo-mA (CAP-mA) by KIO4 in the diluted H2SO4 medium. Kinetic parameters were derived and the reaction conditions were studied. The results indicated that the catalytic reaction is first-order for both Ir(IV) and chlorophosphonazo-mA with the apparent activation energy of 6.912 kJ/mol. The linear range of the method was 0.002 5-0.015 μg/mL for Ir(IV) with the detection limit of 6.38 × 10-6 μg/mL. Many of the common ions did not interfere with the determination except for Ru(III) and Rh(III) at the equal amount as Ir(IV). The relative standard deviation was 1.48% (n=11) for the determination of 0.20 μg/25 mL Ir(IV). The method was applied to the determination of iridium in the metallurgy products, and the results agreed well with those obtained by AAS.