Detection And Analysis Of Heavy Metal Cadmium In Soil By Laser-induced Breakdown Spectroscopy

In recent years,with the acceleration of Chinese industrialization,heavy metal pollution(Cd,Pb,Cr,Cu)in soil has become increasingly serious,resulting in increased soil cadmium(Cd)pollution.Cd is a highly toxic element,and will eventually enrich into the human body with the food chain,seriously threatening human health.Therefore,the development of a new and rapid method for substance detection is urgently needed.Laser-induced Breakdown Spectroscopy(LIBS)is a new photoluminescence technology,can detect trace elements in soil in suit and has great potential in the field of soil heavy metal detection.With laser performance boost,the LIBS technology has got rapid development,but duo to the rich content of element in soil,its physical and chemical properties are complicated.When using LIBS to determine the element content of soil,it is easily affected by matrix effect and self-absorption effect.Therefore,the detection of heavy metals in soil by LIBS still has low repeatability and poor detection accuracy.This article improves the spectral characteristics of LIBS from two aspects,theoretical analysis and experimental exploration,and uses two quantitative analysis methods and several model evaluation methods to analyze the advantages and disadvantages of the two,which provides a new idea for improving the quantitative analysis of LIBS.The main work of this article is:(1)This paper mainly introduces the technical principle of laser-induced breakdown spectroscopy in analysis,and the relationship between characteristic spectral lines and background noise over time,which provides theoretical support for the setting and optimization of experimental parameters.(2)We theoretically analyzed the evolution characteristics of the plasma and the broadening characteristics of the characteristic spectrum.According to the temperature change of the plasma and the broadening characteristics of the linear spectrum,it can guide us to correct the linearity of the spectrum to reduce the fluctuation of the spectrum and improve the repetition rate of the experiment.(3)This paper analyzes the spectral characteristics of Cd in soil.From the experiments,we found that the changes of particle size and water content in soil have a greater impact on the spectral intensity of Cd,and we studied the spectral characteristics of the two at Cd II 214.41 nm.It is found that the effect of particle size changes is more obvious,and under certain conditions,the smaller the particles,the higher the spectral intensity.We can use this feature to classify soils in different states.This article mainly uses this feature to select soils with more suitable sizes particles are used for quantitative analysis.(4)Two analysis methods are used for quantitative analysis.The fitting R~2 of the traditional single calibration is 0.97,and comprehensive analyze the three samples in the prediction set,find that the traditional single calibration method has a certain deviation in the accuracy of element calibration,and the predicted sample concentration varies greatly,indicating that the method is not stable enough and is easily affected by factors such as matrix effects and element self-absorption.However,compared with the traditional single calibration,the maximum likelihood fit R~2 in quantitative analysis reach to 0.99,the deviation of the predicted concentration is smaller.At the same time,the detection limit for the Cd element has also been decreased to 7.84 ppm,which has basically reached the domestic three-level soil testing standard,and the quantitative analysis performance of Cd element has been greatly improved.