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

A new catalytic spectrophotometric method for the determination of trace iridium was established based on its catalytic effect on the oxidative fading reaction between methyl green and potassium periodate in H3PO4 and HAc-NaAc (pH 5.7) cushion solution.A linear relationship was obtained between the absorbency difference A of non-catalytic reaction and catalytic reaction and the concentration of Ir(Ⅳ) in the range of 0～2.0 μg/25 mL.The detection limit was 2.969×10-10 g/mL.The relative standard deviation for the determination of 1 μg/25 mL of Ir(Ⅳ) was 1.7% (n=11).The kinetic parameters were determined.The catalytic reaction was first-order to Iridium(Ⅳ) with the apparent rate constant as 4.613×10-4/s and apparent activation energy as 40.56 kJ/mol.The method can be used in the determination of trace Iridium (Ⅳ) in molecular sieves and activated carbon.The recoveries were in the range of 97.9%～104.4%.This method can meet the requirement of the trace amount analysis.