Determination of Trace Iridium by Catalytic Kinetic Spectrophotometry with Potassium Periodate Oxidatizing Methyl Purple in the Presence of Irodium-catalysis

In diluted H2SO4 and heating at 95 ℃,the trace iridium can catalyze discoloured reaction of the potassium periodate oxidatizing methyl purple.According to this phenomenon,a new method using catalytic kinetic spectrophotometry to the determination of iridium has been established.Optimum experimental conditions were discussed and kinetic parameters of this catalytic reaction were determined.The difference of ΔA between non-catalytic reaction absorbency A0 and catalytic reaction absorbency A at 518 nm remains a good linear relationship with ρ,the mass concentration of iridium in the range of 0.0 to 0.06 μg/mL.The detection limit is 2.833 × 10-10 g/mL.The kinetic parameters of this reaction were also determined and the result showed it was a quasi-first-order kinetics reaction.The apparent ratio constant of this reaction was 1.345 × 10-3s-1,and the apparent activation energy of the reaction was 33.81 kJ/mol.The method has been applied to the determination of trace iridium in molecular sieves and active carbon.The recovery ratio was about 100.0% ～ 104.2%,which met the request of the trace analysis.