Colour Reaction of Iridium(III) with 2-(5 -Bromo-2-pyridylazo)-5 -dimethylamino-aminobenzene and Its Application

The colour reaction of iridium(Ⅲ) with reagent 2 _ (5 _ bromo _ 2 _ pyridylazo) _ 5 _ dimethylamino _ amino_ benzene(5 _ Br _ PADMA) was investigated. In the HAc-NaAc medium at pH 4.75～6.00 iridium(Ⅲ) reacts with 5 _ Br _ PADMA to form a stable red complex, in which the stoichiometric ratio of iridium(Ⅲ) to 5 _ Br _ PADMA is 2∶1. In the medium of 0.6 mol/L H2SO4 the complex has a maximum absorption at 558 nm and an apparent molar absorptivity of 5.1×104 L/(mol·cm). Beer's law is obeyed in the range of 0～0.8 mg/L for iridium(Ⅲ). No significant interference of common anions and cations was observed except Fe3+, Co2+ and Ni2+, which interference can be eliminated using EDTA as a masking agent. On these grounds a method for the determination of trace iridium(Ⅲ) was established in a binary complex system by spectrophotometry. The method is simple, selective and sensitive.