Determination of trace iridium (IV) by catalytic kinetic spectrophotometry with potassium periodate-malachite green

Iridium (Ⅳ) can catalyze the fading reaction of potassium periodate with malachite green at 95 ℃ in diluted sulfuric acid medium. Based on this phenomenon, a catalytic kinetic spectrophotometric method for the rapid determination of iridium (Ⅳ) was established. Optimum experimental conditions were discussed and kinetic parameters were determined. Under selected experimental conditions, the absorbence difference ΔA between non-catalytic reaction system (A0) and catalytic reaction system (A) at 618 nm remained good linear relationship with iridium (Ⅳ) concentration in the range of 0-0.06 μg/mL and the detection limit was 1.3×10-10 g/mL. This catalytic reaction was pseudo first order reaction, whose apparent ratio constancy was 1.850×10-4/s and apparent activated energy was 48.03 kJ/mol. The method was applied to the determination of trace iridium (Ⅳ) in molecular sieves and active carbon with the recovery below 103 % and relative standard deviation of 2.2 % and 1.9 %, respectively.