Detection Of Heavy Metals In Soil By LIBS Based On Chemometric Methods

The soil contaminated by heavy metals contain a large number of elements,such as lead,chromium,cadmium and copper,which are harmful to human health through biological enrichment.Therefore,it is necessary to seek a rapid and accurate method to detect heavy metals in contaminated soils for monitoring and preventing heavy metal pollution in soils.Laser-induced breakdown spectroscopy(LIBS),as a highly sensitive detection technology,becomes one of the most potential analytical methods for detecting heavy metal elements in contaminated soils because of its advantages of simple sample,real-time and on-line multi-element analysis.As a complex and large data analysis method,chemometric can overcome the matrix effect and further improve the accuracy of LIBS spectral analysis.Therefore,the combination of chemometric and LIBS technology has obvious advantages in the analysis of heavy metals in soil.This thesis focused on the qualitative and quantitative analysis of heavy metal elements in contaminated soils from near the Northwest Lead-Zinc Plant,based on LIBS technology and the chemometric method.The following two works have been carried out:The LIBS spectra of soil samples from seven sites near Lead and Zinc Plant in Baiyin were measured and analyzed.The cluster analysis of samples was carried out based on principal component analysis(PCA).The standard addition method(SAM)was used to analyze the mass concentration of Pb in contaminated soil,and the partial least squares(PLS)method was used to improve the accuracy.The LIBS measurement results are evaluated by ICP-AES measurement results.The evaluations imply that the relative error for the SAM measurements are less than 20.9% and less than 16.4% for the PLS measurements.The mass concentrations of Lead and copper in contaminated soils were predicted using the random forest regression(RFR)and generalized regression network(GRNN),respectively.The accuracy of prediction analysis was improved by combining PLS with GRNN.Compared with that using GRNN,the linear correlation of the analysis results increases from 0.927 to 0.972,which provides a reliable method to analysis large-scale soil applied LIBS technology.