2-(5-溴-2-吡啶偶氮)-5-二甲氨基苯胺激光热透镜光谱法测定痕量铑的研究

摘要

A novel method for the determination of trace rhodium by laser thermal lens spectrometry (LTLS) based on the sensitive color reaction between rhodium(Ⅲ) and 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA)was established.The experiment results showed that in a media of pH 3.6-6.0 HAc-NaAc buffer solution,rhodium (Ⅲ) can react with 5-Br-PADMA to form a violet-red complex.The complex can be changed into another green-blue proton species possessing a high abosorption characteristics in 1.2 mol/L HClO4.The optimal concentrations of HClO4,HCl,H2SO4 or H3PO4 were found to be 0.6-3.6 mol · L-1 for HClO4,0.6-3.0 mol/L for HCl,1.2-4.0 mol/L for H2SO4 and 1.8-4.5 mol/L for H3PO4,respectively.The maximum absorption wavelength was 612 nm which matched well with the output wavelength(632.8 nm) of He-Ne laser.The analytical curve was linear in the concentration range of 5-140 μg/L for rhodium,and the detection limit was 1.1 μg/L.The method,having high sensitivity and good selectivity,was applied in the determination of trace rhodium in the rhodium-carbon catalyst with satisfactory results.%基于铑(Ⅲ)与2-(5-溴-2-吡啶偶氮)-5-二甲氨基苯胺(5-Br-PADMA)的高灵敏显色反应,建立了激光热透镜光谱法测定痕量铑的新方法.实验表明,在pH 3.6～6.0的HAc-NaAc缓冲介质中,Rh(Ⅲ)与5-Br-PADMA显色形成紫红色铑络合物；继续以1.2 mol/L HClO4酸化后,可转变为另一种具有较高吸收特性的绿蓝色质子化型体,其最大吸收波长位于612 nm处,与所用He-Ne激光器的输出激光波长(632.8 nm)能较好匹配.铑的质量浓度在5～140 μg/L范围内与热透镜信号强度呈良好的线性关系,检出限(S/N=3)为1.1μg/L.该方法灵敏度高、选择性好,用于铑炭催化剂中痕量铑的测定,结果满意.