激光诱导击穿谱检测土壤微量铜元素污染研究

理论分析激光诱导击穿光谱(LIBS)的特性，研究谱线信噪比随激光能量和样品属性变化的规律，对土壤样品中的微量Cu元素进行实验测量有重要意义。实验采用的烧蚀激光波长为1 064 nm，脉冲宽度约10 ns，重复率为1 Hz。实验证实背景热辐射和元素特征辐射具有不同的空间变化规律，通过在空间上将两者分离获得较高的信噪比。当激光脉冲能量为40 mJ时，实验采用的土壤样品的最佳测量位置为距离火花中心0.75 mm处，选取Cu 324.75 nm和Cu 327.39 nm作为分析线，对含微量Cu元素土壤样品进行测量。采用内标法对测量结果进行定量分析，得到土壤中Cu元素的检测限可达到67 mg·kg-1，满足国家土壤环境质量标准规定的二级土壤中Cu含量的要求。实验结果表明选择最佳光谱测量位置的方法能够有效提高信噪比，满足土壤中微量Cu污染检测的需求。

Research on Laser Induced Breakdown Spectroscopy for Detection of Trace Cu in Polluted Soil

In the present work, spatial character of emission spectrum was analyzed, the effect of laser energy and samples at-tribute on the best detection position for the highest signal-to-noise ratio was studied, and .some experimental investigations with LIBS technique to detect trace Cu in polluted soil were carried out in our laboratory. A Q-switched Nd " YAG laser operating at 1 064 nm with pulse width of 10 ns and repetition frequency of 1 Hz was utilized. The laser pulse was focused by lens with focal length of 10 cm to generate microplasmas on the surface of printed circuit board and soil samples. The sample was adjustable by vernier construction to detect the emission spectrum of the microplasrnas from different position. Experiments showed that the intensity of thermal radiation and atomic radiations evolved differently while the detection position changed. It was verified that thermal radiation reduced rapidly with the distance from the center of spark increasing, while the intensity of atomic radiations increased firstly and decreased after intensity maximum was reached. The method of separating thermal radiation and atomic ra-diations in space brought on high signal-to-noise ratio. It was found that the best detection position was 0. 75 mm off the center of the spark for soil sample while the laser energy was 40 mJ, and the distance increased with the growth of laser energy. WithCu 324. 75 nm and Cu 327. 39 nm as the analysis lines, the best detection position was selected to detect trace Cu pollution in soil. Internal standard method was used to determine the relation between Cu concentration and its intensity. It was concluded that the detection limit of Cu in soil was 67 mg·kg~(-1),which is below the trace element thresholds for Class 2 soil defined in the Environmental Quality Standard for Soil in China. It was proven an effective way to achieve higher signal-to-noise ratio by adjus-ting the location of spectral measurements. This method was viable for trace Cu detection in polluted soil.