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
HAN Quan1,2, HUO Yan-yan1, YANG Xiao-hui1, YANG Na1
1. Department of Chemistry, Xi'an University, Xi'an 710065, China; 2. School of Chemistry and Materials Science, Shaanxi Normal University, Xi'an 710062, China
Abstract：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%.
韩权, 霍燕燕, 杨晓慧, 杨娜. 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[J]. 冶金分析, 2020, 40(5): 20-25.
HAN Quan, HUO Yan-yan, YANG Xiao-hui, YANG Na. 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. , 2020, 40(5): 20-25.
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