Study On Analyses Of Soil Contaminants Using Laser-induced Breakdown Spectroscopy

Recently,the food and ecological securities are both threatened by deteriorating problems of soil pollution,which make the detection of the soil pollution informations more and more significant.With the drawbacks of time consuming and complex sample pretreatment,the conventional detection methods are difficult to achieve quick and big data analyses.As a new versatile technology,laser induced breakdown spectroscopy(LIBS)has been a hotspot in the analysis of heavy metals in soil due to its unique features of rapid analysis,simple sample pretreatment and convenient operation.However,bad limite of detection(LOD),matrix effect,self-absorption effect and spectral interference make LIBS not satisfy the requirement of practical quantitative analysis.To address these problems,some solutions were proposed to improve the abilities of LIBS in this thesis.The detailed contents are as follows:A classification-calibration method was proposed to solve the problem of matrix effect in quantitative analyses of LIBS.A classification method assisted with supported vector machine was used to classify different types of soil firstly,and the accuracy were reached to 100%.Based on the classification results,LIBS was combined with standard addition method and wavelet transform algorithm to improve the accuracy of quantitative analyses.For Pb element in different kinds of soil,the root-mean-square error of prediction(RMSEP)was improved significantly from larger than 300 ppm to lower than 40 ppm.LIBS assisted by laser induced fluoresence(LIF)was used to solve the problem of spectral interference and poor detection sensitivity.The spectral interferences of Fe,Ti and Mn elements were eliminated in the determination of Pb in soil by using a resonant laser of 283.21 nm and a long dealy time of 14 ?s.the R2 was improved from 0.62 to 0.98 and the LOD was improved from 10 ppm to 0.6 ppm,respectively.Furthermore,a method of repeated LIF was proposed to further improve the sensitivity,and the LOD of Pb element determination was reached to 0.143 ppm by dual-LIF(DLIF).To detect available heavy metals in soil,a multi-sample pretreatment process based on solid-liquid-solid transformation method was proposed.Using this sample preparation method,the LOD of available Cd and Pb elements in soil were reached to 0.067 ppm and 0.940 ppm,respectively under single pulse LIBS,which were both better than the environmental quality standard for soils in China.Finally,a spatially resolved collecting device was used to study the self-absorption distributions of the high concentration elements in soils.It was found that the self-absorption effect distributed inhomogeneously in the plasma,and the self-absorption effect in the upper part of the plasma was much more serious than that in the lower part.By taking advantage of this distribution differences and the spatially resolved LIBS technology,the self-absorption effect was reduced effectively.The quantitative analysis results of K element in soil proved that,the R2 and was improved from 0.8477 to 0.9891 and the RSD was improved from 22.9% to 9.2%,respectively.In this thesis,the standard addidtion,laser indued fluoresence,solid-liquid-solid transformation and spacially resolved LIBS were studied,and applied to solve the problems of matrix effect,spectral interference,detection sensitivity and self-absorption effect.These methods improved the accuracy,precision and LOD of quantitative analyses in soil,which will lay a foundation for practical application of LIBS in the field of soil contaminants detection.