2-(5-硝基-4-甲基-2-吡啶偶氮)-5-二甲氨基苯胺激光热透镜光谱法测定钴的研究及其应用

在pH 4.0~7.0的HAc-NaAc缓冲介质中,并在50%乙醇存在下,Co(Ⅱ)与新试剂2-(5-硝基-4-甲基-2-吡啶偶氮)-5-二甲氨基苯胺(5-NO₃-4-CH₃-PADMA)反应形成紫红色配合物;钴配合物形成后,当以强酸酸化,提高酸度至1.8 mol/L H₂SO₄介质,可转变为另一种具有较高吸收特性的绿蓝色质子化形体,最大吸收波长位于622 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,据此建立了激光热透镜光谱法测定痕量钴的新方法。钴质量浓度在3~100 ng/mL范围内与分析信号呈良好的线性关系,检出限为1.0 ng/mL。常见金属离子不干扰钴的测定,特别是与钴伴生的铁、镍和铜等元素有较高的允许量,150倍量的Fe³⁺和Ni²⁺、5倍量的Cu²⁺等不干扰钴的测定。实验方法应用于矿石中痕量钴的测定,结果与推荐值(原子吸收光谱法测定结果)一致,相对标准偏差在0.46%~1.46%之间。

Study on the determination of cobalt by laser thermal lens spectrometry using 2-(5-nirtro-4-methyl-2-pyridylazo)-5-dimethylaminoaniline as a new chelating agent and its application

In HAc-NaAc buffer solution at pH 4.0-7.0, Co(Ⅱ) could react with new reagent 2-(5-nitro-4-methyl-2-pyridylazo)-5-dimethylaminoaniline (5-NO₃-4-CH₃-PADMA) to form purple red complex in presence of 50% ethanol. When the acidity increased to 1.8 mol/L H₂SO₄ medium, the formed cobalt complex could be converted to another green-blue protonation substance with relatively high absorption characteristics. The maximum absorption wavelength located at 622 nm, which could be well matched with the output laser wavelength (632.8 nm) of He-Ne laser. Based on this, a new determination method of trace cobalt by laser thermal lens spectrometry was established. The mass concentration of cobalt in range of 3-100 ng/mL showed good linear relationship to the signal intensity of thermal lens. The detection limit was 1.0 ng/mL. The common metal ions did not interfere with the determination of cobalt. Particularly, the iron, nickel and copper, which were associated with cobalt, had highly tolerant amount: 150 fold of Fe³⁺ and Ni²⁺ and 5 fold of Cu²⁺ had no interference with the determination of cobalt. The proposed method was applied to the determination of trace cobalt in ores, and the found results were consistent with the recommended values (the determination results of atomic absorption spectrometry). The relative standard deviations (RSD) were between 0.46% and 1.46%.