Colour reaction of Iridium(III) with 2-(5-Iodine-2-pyridylazo)-5-dimethylaminoaniline and its application

The highly sensitive color reaction of 2-(5-iodine-2-pyridylazo)-5-dimethylaminoaniline(5-I-PADMA) with iridium(III) has been studied.The experimental results show that iridium(III) reacts with 5-I-PADMA in a buffer solution of HAc-NaAc at pH 5.6 ~ 7.3 to form a stable 1:2 complex,and it shows a maximum absorption peak at 475 nm.The complex can be changed into another stable proton species possessing a higher absorption characteristic by acidification with a mineral acid(e.g.HCl,H2SO4,HClO4,H3PO4).The optimal concentrations of HCl,H2SO4,HClO4 or H3PO4 are found to be 0.6 ~ 6.0 mol/L HCl,0.24 ~ 3.9 mol/L H2SO4,0.6 ~ 3.9 mol/L HClO4 and 0.6 ~ 7.2 mol/L H3PO4 respectively.The apparent molar absorptivity is 1.01×105 L · mol-1 · cm-1 at the maximun absorption of 616 nm.Beer's law is obeyed in the range of 0 ~ 0.7 μg/mL for iridium.The method is convenient,fast and highly sensitive.It has been successfully applied to the determination of trace iridium(III) in catalyst with satisfactory results.