Laser-induced breakdown spectroscopy (LIBS) is a spectrochemical analysis method based on analyzing spectra of plasmas that generated by pulsed lasers. With its advantages of fast, real time, and stand-off analyses, LIBS has been widely applied in many areas, such as steels, plastics, ceramics, and soil. However, the complex and serious spectral interference influenced the accuracy of quantitative analysis in LIBS.

To address this problem, the laser-induced breakdown spectroscopy research team used LIBS assisted by laser-induced fluorescence (LIBS-LIF) technology to enhance the spectral intensities of the interfered lines, selectively. Utilizing this selective enhancement effect, all the interference lines could be eliminated. As an example, the interfered Pb I 405.78 nm line in soil plasma was studied in this work. Spectra of Pb I 405.78 nm in soil at different delay times were obtained and compared, serious spectral interference was found at the short delay time, but all the spectral line disappeared at a longer delay time. These phenomena indicated that, if the Pb I 405.78 line was selectively enhanced at a longer delay time, the spectral interference could be eliminated. Quantitative analysis of trace Pb element in soil was also carried out. The results showed that, in the Pb concentration range of 14–94 ppm, the determination coefficient (R2) of LIBS-LIF was improved from 0.6235 to 0.9802 of conventional LIBS, as well as the limit of detection (LOD) of Pb element calculated by the 3σ criterion was improved from 24 ppm to 0.6 ppm. These demonstrate that LIBS-LIF can eliminate spectral interference effectively and improve the ability of LIBS to detect trace heavy metals in soil.

This work was financially supported by the National Instrumentation Program of China (No. 2011YQ160017) and National Natural Science Foundation of China (No. 61575073), which had been published in ASC journal of Analytical Chemistry with the title of “Spectral Interference Elimination in Soil Analysis Using Laser-induced Breakdown Spectroscopy Assisted by Laser-Induced Fluorescence”.

Enclose: Rongxing Yi, Jiaming Li, Xinyan Yang, Ran Zhou, Huiwu Yu, Zhongqi Hao, Lianbo Guo, Xiangyou Li *, Xiaoyan Zeng and Yongfeng Lu, Spectral Interference Elimination in Soil Analysis Using Laser-induced Breakdown Spectroscopy Assisted by Laser-Induced Fluorescence, Analytical Chemistry, 2017, 89 (4), 2334–2337


                                Fig.1. The principle of LIBS-LIF and the elimination of spectral interference