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 pres‐ence of 50% ethanol .When the acidity increased to 1.8 mol/L H2 SO4 medium ,the formed cobalt complex could be converted to another green‐blue protonation substance with relatively high absorption characteris‐tics .The maximum absorption wavelength located at 622 nm ,which could be well matched with the out‐put laser wavelength (632.8 nm) of He‐Ne laser .Based on this ,a new determination method of trace co‐balt 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 ap‐plied to the determination of trace cobalt in ores ,and the found results were consistent with the recommen‐ded values (the determination results of atomic absorption spectrometry ) .T he relative standard deviations (RSD) were between 0.46% and 1.46% .%在pH 4.0～7.0的HAc‐NaAc缓冲介质中，并在50％乙醇存在下，Co槍与新试剂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 H2 SO4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／m L范围内与分析信号呈良好的线性关系，检出限为1.0 ng／m L。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。
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