以2-(5-溴-2-吡啶偶氮)-5-二甲氨基苯胺作螯合剂浊点萃取-激光热透镜光谱法测定水中痕量钴

钴是生命体必需的微量元素,研究建立水样中钴的测定方法具有重要意义。在pH 5.0的醋酸-醋酸钠缓冲介质中,于60℃水浴中加热10min, 螯合剂2-(5-溴-2-吡啶偶氮)-5-二甲氨基苯胺(5-Br-PADMA)与钴(II)反应生成配位比为2∶1的疏水性螯合物Co(II)-5-Br-PADMA,其最大吸收波长位于611nm,用非离子表面活性剂TritonX-114为萃取剂进行浊点萃取(CPE),将该疏水性螯合物萃取到表面活性剂胶束相中,在相分离之后,以0.45mL 2mol/L HCl-乙醇溶液溶解胶束相,转入光程为5mm的自制石英吸收池中,以单模He-Ne激光器(λ=632.8nm)做激发和探测光束进行热透镜光谱法(TLS)测定,建立了浊点萃取-激光热透镜光谱法(CPE-TLS)测定超痕量钴的方法。在优化条件下,热透镜光谱信号强度与钴(II)质量浓度在0.40~6.0ng/mL范围内呈良好的线性关系,相关系数为0.9978,检出限为0.05ng/mL。按富集前后溶液体积比值计算其浓缩因子为22。将实验方法用于湖水和温泉水中钴含量的测定,结果的相对标准偏差(RSD,n=6)小于4%;结果与电感耦合等离子体质谱法(ICP-MS)基本一致;加标回收率在96%~101%之间。

Determination of trace cobalt in water by laser thermal lens spectrometry after cloud point extraction using 2-(5-bromo- 2-pyridylazo)-5-dimethylaminoaniline as chelating agent

Cobalt is an essential trace element for living species, so the establishment of determination method for cobalt in water sample is of great importance. In the buffer medium of HAc-NaAc at pH 5.0, the chelating agent 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) could react with Co(II) to form a hydrophobic chelate Co(II)-5-Br-PADMA with coordination ratio of 2∶1 after heating in water bath at 60℃ for 10 min. Maximum absorption wavelength was 611nm. The nonionic surfactant Triton X-114 was selected as extraction agent for cloud point extraction (CPE). The generated hydrophobic chelate could be extracted into surfactantmicelle phase. After phase separation, the micelle phase was dissolved with 0.45mL of 2mol/L HCl-ethanol solution, which was then transferred into a self-made quartz cell with optical path of 5mm. He-Ne laser (single model, λ=632.8nm) was employed both as exciting and probing beam for the thermal lens spectrometry (TLS). Consequently, a new determination method of ultra-trace cobalt by CPE-TLS was established. Under the optimized conditions, the TLS signal intensity of Co(II) had good linear relationship with the corresponding mass concentration in range of 0.40-6.0ng/mL. The correlation coefficient was 0.9978. The limit of detection was 0.05ng/mL. Based on the volume ratio of solution before and after enrichment, the enrichment factor was calculated, i.e., 22. The proposed method was applied for the determination of cobalt content in lake water and thermal spring water. The relative standard deviations (RSD, n=6) of determination results were less than 4%. The found results were consistent with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The spiked recoveries were between 96% and 101%.