水溶液中金属元素的激光诱导击穿光谱的检测分析

文章对竖直流动的CuSO₄和Pb(NO₃)₂水溶液样品表面的激光诱导击穿光谱的（简称LIBS）特性进行了观测分析。实验中采用的烧蚀激光波长为532 nm，脉冲宽度为10 ns，重复频率为10 Hz；LIBS信号的探测通过一色散相加型双光栅单色仪、Boxcar和PMT的组合来完成。通过对水溶液中金属元素的LIBS信号随时间和能量演化规律的分析，初步确定了系统 的最佳烧蚀能量和最佳探测延时。受样品表面附近空气击穿时氧元素信号的影响，实验对Cu和Pb各自的击穿位置进行了优化。在分析影响LIBS光谱探测因素的基础上，进一步优化了系统的工作条件和探测 参数。通过对不同浓度下LIBS信号的探测分析，初步确定了系统对Cu与Pb的最低检测浓度，分别约为31，50 ppm(μg·mL-1)。文章还对将LIBS技术运用到海水中重金属的实时在线检测的可 行性进行了讨论。

Detection of Metal Ions in Water Solution by Laser Induced Breakdown Spectroscopy

Environmental concerns about the hazardous heavy metals in seawaters have been greatly increased in these years. To evaluate the potential application of laser induced breakdown spectroscopy (LIBS) to on-line toxic metals pollution monitoring in ocean, some experimental investigations with LIBS technique to detect metal ions in CuSO₄ and Pb(NO₃) ₂ water solutions have been carried out in our laboratory. A Q-switched Nd∶YAG laser operating at 532 nm with pulse width of 10 ns and repetition frequency of 10 Hz was utilized to generate plasma on a flowing liquid surface. The ensuing plasma emission was coupled by a quartz lens to a double grating monochromator and recorded with a PMT in conjunction with a computer controlled boxcar integrator. The temporal characteristic of the laser induced plasma and the power dependence of LIBS signal were investigated. The operation condition was improved with the optimal ablation pulse energy and the delay time for LIBS signal detection. The ablation location was varied to achieve better LIBS signal. The optimized ablation location for lead was found to be different from that for copper due to the breakdown of the ambient air. The detection limit of metal ion in water solution under the optimized operation conditions was found to be 31 ppm for copper and 50 ppm for lead. The experimental results proved that the flexibility of LIBS has the potential to be applied to the detection of toxic metals in seawaters, but the limits of detection for each element should be improved further to make a practical application of LIBS in this field.