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 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 (Cu), lead (Pb) and chromium (Cr) were used to directly analyze 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 (ICP-OES) was poor. To improve the analysis accuracy, the calibration-free LIBS (CF-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. Our results demonstrate that LIBS is an efficient rapid method for mapping the spatial contaminated distribution of heavy metal elements and giving us the clear direction to treat heavy metal pollution.