Mapping analysis of heavy metal elements in polluted soils using Laser Induced Breakdown Spectroscopy

Laser-induced breakdown　spectroscopy(LIBS) has become a powerful technology　for quantitative analysis of the toxic heavy　metals in soils due to its excellent a attributes　of rapid analysis speed, simultaneous multi-element assay, and low-cost detection with slight sample preparation. In this work, LIBS was applied to analyze the spatial concentration distribution of toxic heavy metals in soils around a smelter. The spectral lines of copper, lead and chromium were used to directly analyzed the concentration distribution in soils around the smelter. The relevance between the spectral line intensities of Cr and the total concentrations detected by inductively coupled plasma optical emission spectrometry was poor. To improve the analysis accuracy, the calibration-free LIBS method combined with Saha equation was used. Compared with the preliminary analysis result of spectral line intensities, the concentration ratios of Cr/Si obtained from CF-LIBS showed a good correlation with the total concentrations. Then, the map of the spatial relative concentration distribution of Cr superposed on the aerial view of the locations was established.

激光诱导击穿光谱（Laser-induced breakdown spectroscopy, LIBS）凭借分析速度快、可同时实现多元素检测、样品前处理要求低且检测成本低廉等突出优势，已成为土壤中有毒重金属定量分析的强有力技术。本研究将LIBS技术应用于某冶炼厂周边土壤内有毒重金属的空间浓度分布分析。选取铜、铅、铬的特征谱线，对该区域土壤中的元素浓度分布进行直接分析。但结果显示，铬的谱线强度与电感耦合等离子体发射光谱（inductively coupled plasma optical emission spectrometry）测得的重金属总浓度之间相关性较差。为提升分析精度，本研究采用结合萨哈方程（Saha equation）的无标样激光诱导击穿光谱（calibration-free LIBS, CF-LIBS）方法。相较于仅基于谱线强度的初步分析结果，通过CF-LIBS方法得到的铬/硅浓度比值与总浓度之间呈现出良好的相关性。最终构建了叠加有采样点位航拍影像的铬元素空间相对浓度分布图谱。