4-(5-硝基-2-吡啶偶氮)-1,3-二氨基苯与铑(Ⅲ)显色反应的研究及其应用

Study on the color reaction of rhodium with 4-(5-nitro-2-pyridylazo)-1,3-diaminobenzene and its application

研究了新合成试剂4-（5-硝基-2-吡啶偶氮）-1,3-二氨基苯（5-NO2-PADAB）与铑（Ⅲ）的显色反应。结果表明,在pH 3.3-4.7的乙酸-乙酸钠缓冲介质中,5-NO2-PADAB与铑形成2∶1的紫红色络合物,其最大吸收波长位于524 nm。该络合物在1.2 mol/L HClO4介质中可质子化转变为另一种型体的紫蓝络合物,最大吸收波长红移至580 nm,其表观摩尔吸光系数提高至1.52×10^5L.mol^-1.cm^-1,以EDTA为掩蔽剂,大量常见金属离子不干扰测定。铑含量在0-0.8μg/mL内符合比尔定律。所拟方法可应用于催化剂中微量铑的测定。

A new reagent 4-（5-nitro-2-pyridylazo）-1,3-diaminobenzene（5-NO2-PADAB） is recommended for the determination of rhodium（Ⅲ）.It is shown that 5-NO2-PADAB reacts with rhodium at pH 3.3～4.7 to form a violet-red complex showing a maximum absorption at 524 nm.The complex can be changed into another deeply colored stable species by addition of mineral acid.The maximum absorption of the complex shifts to 580 nm in a medium of 1.2 mol/L HClO4.The apparent molar absorptivity is 1.52×10^5 L·mol^-1·cm^-1.Beer′s law is obeyed inthe concentration range of 0 - 0.8μg/mL for rhodium. The method is highly sensitive and selective. Most common ions do not interfere with it. It has been successfully applied to the determination of trace rhodium in catalysts with satisfactory results.