2-(5-溴-4-甲基-2-吡啶偶氮)-5-二甲氨基苯胺与镍显色反应的研究

研究了新试剂2-(5-溴-4-甲基-2-吡啶偶氮)-5-二甲氨基苯胺(5-Br-4-CH₃-PADMA)与镍的显色反应,建立了分光光度法测定镍的新方法。结果表明,在 pH 值为 4.2~6.0 的 HAc-NaAc 缓冲溶液中,在阴离子表面活性剂十二烷基硫酸钠(SDS)存在下,镍与 5-Br-4-CH₃-PADMA 形成稳定的组成比为1∶2的紫色配合物,其最大吸收波长位于 567 nm 处。镍的质量浓度在0～0.40 μg/mL范围内遵守比尔定律,校准曲线的线性相关系数r=0.999 2,表观摩尔吸光系数ε=1.22×10⁵ L·mol^-1·cm^-1。以硫脲和氟化铵做掩蔽剂可消除Cu²⁺、Fe³⁺ 和Pd²⁺等离子的干扰。方法用于铝合金中微量镍的测定,结果的相对标准偏差(RSD, n=6)为0.58%~0.98%,并与火焰原子吸收光谱法测定值一致。

Study on color reaction between 2-(5-bromo-4-methyl-2-pyridylazo)-5-dimethylaminoaniline and nickel

The color reaction between a new reagent 2-(5-bromo-4-methyl-2-pyridylazo)-5-dimethylaminoaniline (5-Br-4-CH₃-PADMA) and nickel was studied. A new determination method of nickel by spectrophotometry was established. The experimental results showed that nickel reacted with 5-Br-4-CH₃-PADMA in the presence of anion surfactant sodium dodecyl sulfate (SDS) in HAc-NaAc buffer solution at pH 4.2-6.0 to form a purple complex with stable composition of 1∶2. The maximum absorption wavelength of complex was at 567 nm. The Beer's law was obeyed for nickel with concentration range of 0-0.4 μg/mL. The linear correlation coefficient of calibration curve was r=0.999 2. The apparent molar absorptivity was ε=1.22×10⁵ L·mol^-1·cm^-1. The interference of Cu²⁺, Fe³⁺ and Pd²⁺ could be masked using thiourea and ammonium fluoride. The proposed method was applied to the determination of trace nickel in aluminum alloy. The relative standard deviations (RSD, n=6) were between 0.58% and 0.98%. The found results were consistent with those obtained by flame atomic absorption spectrometry.