以2-(5-氰基-2-吡啶偶氮)-5-二甲氨基苯胺(5-CN-PADMA)做显色剂,建立了双波长叠加分光光度法测定铜的新方法.研究发现,在pH 4.0~5.0的HAc-NaAc缓冲介质中,于室温下,5-CN-PADMA与铜(Ⅱ)即可形成稳定的2∶1紫红色配合物,其吸收光谱呈现两个吸收峰,分别位于548 nm和583 nm处,且两个吸收峰处的吸光度具有良好的加合性,吸光度之和与铜(Ⅱ)质量浓度线性相关.铜(Ⅱ)质量浓度在0~0.8 μg/mL范围内服从比尔定律,双波长测量的表观摩尔吸光系数为1.06×105 L·mol-1·cm-1.应用于铝合金中铜的测定,结果与火焰原子吸收光谱法一致,相对标准偏差(RSD)在0.86%~2.1%之间.
A new method for the determination of copper was established by dual-wavelength overlapping spectrophotometry with 2-(5-cyano-2-pyridylazo)-5-dimethylaminoaniline (5-CN-PADMA) as coloring agent.It was found that 5-CN-PADMA could react with Cu(Ⅱ) at room temperature in HAc-NaAc buffer solution at pH 4.0-5.0 to form stable purple red complex (2∶1).The absorption spectrum of complex had two peaks at 548 nm and 583 nm, respectively.Moreover, the absorbance at two absorption peaks exhibited good additivity.The sum of absorbance was linear to the mass concentration of Cu(Ⅱ).Beer's law was obeyed for the mass concentration of Cu(Ⅱ) in range of 0-0.8 μg/mL.The apparent molar absorptivity in dual-wavelength measurement was 1.06×105 L·mol-1·cm-1.The proposed method was applied to the determination of copper in aluminum alloy, and the results were consistent with those obtained by flame atomic absorption spectrometry.The relative standard deviations (RSD) were between 0.86% and 2.1%.
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