Color reaction of 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene with iridium(III) and its application

The color reaction of 5-(5-iodine-2-pyridylazo)-2,4-diaminotoluene(5-I-PADAT) and iridium(Ⅲ) was investigated by spectrophotometry.The results showed that iridium(Ⅲ) and 5-I-PADAT could form stable complex(1∶2) in HAc-NaAc buffer solution(pH 5.5-6.8).After acidification with strong acid,the complex could be converted to another protonized form with high absorption characteristic,significantly enhancing the sensitivity.In 1.2 mol/L of H2SO4 solution,the complex exhibited two absorption peaks at 542 nm and 584 nm,respectively.The apparent molar absorptivity was e584=5.9×104 L·mol-1·cm-1.Beer's law was obeyed for iridium(Ⅲ) in the range of 0.03-1.0 μg/mL.The proposed method has been applied to the determination of iridium in catalyst.The result was consistent with the reference value and the relative standard deviation(RSD) was 0.52%.