Quantitative Analysis of Cr in Soil by Laser-Induced Breakdown Spectroscopy
LIN Xiao-mei1, CAO Yu-ying1, ZHAO Shang-yong2, SUN Hao-ran1, GAO Xun2*
1. College of Electronics and Electrical Engineering, Changchun University of Technology, Changchun 130012, China
2. College of Science, Changchun University of Science and Technology, Changchun 130022, China
Abstract：In order to improve the spectral intensity and the signal-to-back ratio of the characteristic spectral lines, promote the application of LIBS technology in the detection of trace heavy metals in soil. The experimental parameters in the process of soil analysis were optimized, and the element of Cr was analyzed. The Nd∶YAG laser with an output wavelength of 1 064 nm, the pulse width of 10 ns and pulse frequency of 1~10 Hz was used as the light source to focus the pulse laser on the surface of soil samples to generate laser plasma. Experimental parameters such as laser excitation energy, sample distance from lens and spectrometer collection delay were optimized. Firstly, the spectral intensity and the signal-to-back ratio of the laser energy from 60 to 110 mJ were compared. It was found that the plasma radiation intensity rises first and decreases, and the best experimental results can be obtained when 90 mJ excitation energy is selected. Secondly, the variation of spectral intensity from 5 mm before coke to 5 mm after coke is compared. It was found that when the distance between the sample and the lens was 1 mm after the focus (i. e. the focus position was 121 mm), the characteristic spectral lines and the information to back ratio of Cr elements reached the best. Finally, the influence of the acquisition delay of the spectrometer on the spectral line strength and the signal-to-back ratio were analyzed. The results show that the influence trend of energy on plasma radiation intensity is roughly the same, and the experiment result is best when the collection delay is 1 000 ns. Under the optimum experimental conditions (that is, the laser energy 90 mJ, focus position 121 mm, the acquisition delay 1 000 ns), 12 soil samples containing heavy metal Cr were detected by spectroscopy. Meanwhile, in order to reduce the interference of the external environment, the average values of the spectra obtained from 10 laser ablation positions of the same sample were pretreated. Chromium (Ⅰ) 357.86 nm, chromium (Ⅰ) 425.44 nm and chromium (Ⅰ) 427.49 nm were selected as characteristic lines. The calibration curves of doping concentration and spectral intensity were established. The detection limits of the three lines were 74.62, 64.07 and 67.49 mg·kg-1, respectively. The goodness-of-fit values R2 were 0.98, 0.97 and 0.99, respectively. RMSE was 0.41, 0.33 and 0.35, respectively. At the same time, partial least square method and support vector machine algorithm are introduced to improve the accuracy of calibration model further. The results show that the optimization of experimental parameters improves the quantitative detection parameters of trace elements by LIBS technology. The optimal spectral intensity and signal-to-back ratio are obtained. Good experimental results are obtained by the Lorenz fitting calculation of calibration curve, which has important reference significance for the detection of trace heavy metal elements by LIBS technology.
Key words：Laser induced breakdown spectroscopy; Limit of detection; The goodness-of-fit values; RMSE
林晓梅，曹玉莹，赵上勇，孙浩然，高 勋. 激光诱导击穿光谱技术对土壤中重金属元素Cr的定量分析[J]. 光谱学与光谱分析, 2021, 41(03): 875-879.
LIN Xiao-mei, CAO Yu-ying, ZHAO Shang-yong, SUN Hao-ran, GAO Xun. Quantitative Analysis of Cr in Soil by Laser-Induced Breakdown Spectroscopy. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2021, 41(03): 875-879.
[1] DU Chuang, GAO Xun, SHAO Yan, et al(杜 闯, 高 勋, 邵 研, 等). Acta Physica Sinica(物理学报), 2013, 62(4): 357.
[2] Hamzaoui S, Nouir R, Jaidene N. Journal of Applied Spectroscopy, 2017, 84(1): 82.
[3] ZHOU Xi-lin, WANG Jiao-na, LIU Di, et al(周西林, 王娇娜, 刘 迪, 等). Metallurgical Analysis(冶金分析), 2017, 37(1): 39.
[4] DONG Yan-min(董艳敏). Chemical Enterprise Mangement（化学管理）, 2019，(5): 85.
[5] TIAN Xian-qing, ZHANG Xi-cui, HU Fang-zhi, et al(田先清, 张喜翠, 胡方芝，等). Chemical Research and Application（化学研究与应用）, 2014, 26(2): 160.
[6] Shaik A K, Epuru N R, Syed H, et al. Optics Express, 2018, 26(7): 8069.
[7] LIU Yu-feng, ZHANG Lian-shui, HE Wan-lin, et al(刘玉峰, 张连水, 和万霖, 等). Acta Physica Sinica(物理学报), 2015, 64(4): 205.
[8] SHEN Gui-hua, LI Hua-chang, SHI Ye-hong(沈桂华, 李华昌, 史烨弘). Metallurgical Analysis(冶金分析), 2016, 36(5): 16.
[9] Ghezelbash M, Darbani S M R, Majd A E, et al. Journal of Superconductivity and Novel Magnetism, 2017, 30(7)：56.
[10] LU Cui-ping, LIU Wen-qing, ZHAO Nan-jing, et al(鲁翠萍, 刘文清, 赵南京, 等). Laser & Optoelectronics Progress(激光与光电子学进展), 2011, 48(5): 124.
[11] MENG De-shuo, ZHAO Nan-jing, LIU Wen-qing, et al(孟德硕, 赵南京, 刘文清, 等). Chinese Journal of Lasers(中国激光)，2014, 41(7): 253.
[12] SUN Miao, Guindo, Mahamed, et al(孙 淼，Guindo, Mahamed，等). Journal of Zhejiang University of Science and Technology(浙江科技学院学报)，2019，(5): 373.
[13] LI Yan，ZHAI Kai-hua, LI Yan-li, et al(李 艳, 翟开华, 李艳丽，等). Natural Science Journal of Xiangtan Unversity(湘潭大学自然科学学报)，2018，(3): 86.
