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以5-(5-碘-2-吡啶偶氮)-5-二氨基甲苯(5-I-PADAT)作显色剂,建立了双波长叠加分光光度法同时测定铑、钯的新方法。研究发现,在0.6～1.8 mol/LHCIO4介质中,Pd(II)与5-I-PADAT形成稳定络合物,而在此酸度下,Rh(III)则完全不能反应;在pH4.0～5.2 HAc-NaAc缓冲介质中,Rh(III)与5-I-PADAT可形成稳定紫红色络合物,铑络合物形成后提高酸度至0.24～5.57 mol/L HCIO4介质,该络合物不仅不被分解,而且转化为另一种紫蓝色质子化型体,吸收红移、吸光度显著增大。研究还发现,Rh(III)、Pd(II)与5-I-PADAT形成的络合物,均呈现两个吸收峰,强峰分别位于580 nm和584 nm处,弱峰分别位于538 nm和547 nm处。其各自的强弱峰对应的吸光度之和与溶液中铑、钯的含量具有良好的线性关系。据此,建立了双波长叠加分光光度法同时测得铑、钯新方法。铑和钯的表观摩尔吸光系数分别为εRh=2.76×105L.mol-1.cm-1和εPd=1.14×105L.mol-1.cm-1,灵敏度分别为单波长法测定的1.52倍和1.53倍。铑、钯的质量浓度分别在0～0.5μg/mL和0～1.0μg/mL范围内符合比尔定律。方法用于催化剂中铑和钯的同时测定,结果满意。
A new method for the simultaneous determination of rhodium and palladium by dual-wavelength superposition spectrophotometry was developed by using 5- (5-iodo-2-pyridylazo) -5-diaminotoluene (5-I-PADAT) The results showed that Pd (II) formed a stable complex with 5-I-PADAT in 0.6-1.8 mol / L HClIO4 medium, while Rh (III) HAc-NaAc buffer medium, Rh (III) and 5-I-PADAT can form a stable fuchsine complex, rhodium complex formed after the increase of acidity to 0.24 ~ 5.57 mol / L HCIO4 medium, the complex not only not Is decomposed, and converted to another purple-blue protonated species, absorbing red-shift, absorbance increased significantly. The study also found that the complexes formed by Rh (III), Pd (II) and 5-I-PADAT showed two absorption peaks with strong peaks at 580 nm and 584 nm, weak peaks at 538 nm and 547 nm. The sum of the absorbances corresponding to their respective intensity and peak has a good linear relationship with the content of rhodium and palladium in the solution. Based on this, a new method of simultaneous determination of rhodium and palladium by dual-wavelength superposition spectrophotometry was established. The apparent molar absorptivities of rhodium and palladium were εRh = 2.76 × 105L.mol-1.cm-1 and εPd = 1.14 × 105L.mol-1.cm-1, respectively, and their sensitivities were 1.52-fold and 1.53 times. Beer’s law was obeyed in the range of 0 ~ 0.5μg / mL and 0 ~ 1.0μg / mL respectively for rhodium and palladium. The method was applied to the simultaneous determination of rhodium and palladium in the catalyst with satisfactory results.