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研究了新试剂2-(5-碘-2-吡啶偶氮)-5-二甲氨基苯胺(5-I-PADMA)与铱(Ⅲ)的高灵敏显色反应。结果表明,在pH 5.6～7.3的HAc-NaAc缓冲溶液中,铱(Ⅲ)与5-I-PADMA可形成稳定的1:2配合物,其最大吸收峰位于475 nm;铱配合物形成后,当以适量的无机酸(HC l,H2SO4,HC lO4,H3PO4)酸化,可转变为另一种具有较高吸收特性的质子化形体,其吸收峰红移至616 nm,适宜的酸浓度范围分别为0.6～6.0 mol/L HC l、0.24～3.9 mol/L H2SO4、0.6～3.9 mol/L HC lO4和0.6～7.2 mol/L H3PO4,表观摩尔吸光系数达1.01×105L·mol-1.cm-1,是目前测定铱的高灵敏二元显色体系之一。铱(Ⅲ)含量在0～0.7μg/mL范围内符合比尔定律。本法应用于催化剂中微量铱的测定,结果满意。
The highly sensitive color reaction of 2- (5-iodo-2-pyridylazo) -5-dimethylaminoaniline (5-I-PADMA) with iridium (Ⅲ) was studied. The results showed that the stable 1: 2 complex was formed between iridium (Ⅲ) and 5-I-PADMA in HAc-NaAc buffer solution at pH 5.6-7.3 and the maximum absorption peak was at 475 nm. After formation of iridium complex, When acidified with an appropriate amount of inorganic acids (HC1, H2SO4, HC1O4, H3PO4), it can be converted into another protonated form with higher absorption characteristics. The absorption peak shifts red to 616 nm, and the suitable acid concentration ranges are The apparent molar absorptivity was 1.01 × 105L · mol -1 · cm -1 for 0.6 ~ 6.0 mol / L HCI, 0.24 ~ 3.9 mol / L H2SO4, 0.6 ~ 3.9 mol / L HC104 and 0.6 ~ 7.2 mol / L H3PO4 -1, is currently one of the highly sensitive binary colorimetric systems for the determination of iridium. Beer’s law is obeyed for iridium (Ⅲ) in the range of 0 ~ 0.7 μg / mL. The method is applied to the determination of trace amount of iridium in catalyst with satisfactory results.