Development Of Compact Laser-induced Breakdown Spectroscopy(LIBS) Instrument And Analysis Methods Of Solutions And Soils

Laser Induced Breakdown Spectroscopy?LIBS?is an atomic emission spectroscopy technique.Target substances generate high-temperature plasmas under the excitation of high-energy laser and radiate emission lines of atoms and ions,which can be used to detect elemental composition and content.Compared with the traditional element detection technologies,LIBS has the unique advantages of simple sample preparation,fast detection,simultaneous analysis of multiple elements and minimal consumption,which has become a hot research topic at present.The advantages of LIBS's rapid detection are realized by miniaturized detection equipment,rapid and direct sample preparation methods and multi-element simultaneous analysis.Therefore,this paper has carried out researches on these aspects.In the past,most LIBS researches were carried out based on experimental platforms,which restricted the further development of LIBS.Therefore,the instrumentation of LIBS is a key step to promote the method from mechanism research to practical application.The detection and quantitative analysis of different substances is the main part of LIBS researches,which is closely related to the application value of LIBS in various fields.Considering the development status and existing problems of LIBS,this paper has studied the following contents:?1?Development of laser induced breakdown spectroscopy instrument and measurement and control softwareCurrent LIBS instruments or devices have problems of low integration,cumbersome operation procedures,large size,and high costs.Based on modular design,small high-energy laser,unified control system and embedded software system,this paper developed a LIBS instrument with the features of high integration,simple operation and large energy output.The instrument was designed in modules,which were independent of each other and connected by standardized interfaces.The use of high-energy air-cooled laser further reduced the burden on structure,improved performance,and increased integration of the instrument.The unified control system realized the control and data transmission of all components,streamlined the instrument interface,and could quickly complete the operation of the instrument with the PC software.The LIBS software based on embedded system provided a unified interface for parameter adjustment and data acquisition of LIBS experiment,which realized the functions of spectra acquisition,file operation and qualitative analysis,and improved the automatic capability of the instrument.When analyzing copper ore samples,the content of copper?Cu?and zinc?Zn?elements were determined using the calibration curve method.The detection limits of Cu and Zn were 0.0365%and 39.581?g·g^-1,respectively.The correlation coefficients?R²?were higher than 0.98,and the relative standard deviations?RSDs?were lower than 8%for the two elements.Quantitative analysis models for different types of samples laid the foundation for the application of LIBS instruments.?2?Study on rapid detection method of liquid samples by LIBSThe physical and chemical properties of the material directly affect the quantitative analysis of LIBS.In this paper,LIBS was used to study the rapid detection method and quantitative analysis of the prepared solutions.Aiming at the low detection limit and low repeatability caused by plasma quenching effect,sputtering and surface ripple of liquid sample directly tested by LIBS,a rapid hydrogel preparation method based on superabsorbent compound was proposed.This method enabled LIBS to quickly detect liquid samples.The experimental results showed that the detection limits of Al,Cu and Cr were 1?g·g^-1,25?g·g^-1 and 5?g·g^-1,respectively,and the RSD was 16.8%,26.6%and 14.4%,respectively,which improved the poor detection limits and repeatability caused by quenching effect,liquid sputtering and surface ripple.?3?Multi-element quantitative analysis of soils based on calibration curve and multivariate regressionIn order to quantitatively detect the Si,Al,Mg,Ca,Na,K,Mn,Ba,Ti,Cr,Cu,Sr and P elements of soils under complex matrix conditions,the calibration curve,partial least squares regression?PLSR?and support vector regression?SVR?were used to quantitatively analyze various elements in soil samples from different regions,and the results were studied.Among the quantitative analysis of calibration curve,the correlation coefficients of Ca,K,Mg,Na and Sr elements were higher than 0.90,while the elements of Al,Ba,Cr,Cu,Mn and Ti had bad linear relationships due to the influence of matrix effect.In multivariate regression analysis,the quantitative analysis models were established with 14 spectral band data and full spectrum data as input variables,respectively,and the robustness of the models were evaluated.The experimental results showed that the SVR model had a better root mean square error and a higher correlation coefficient?R²?for the training data and test data,and the prediction results of the 13 elements in the unknown sample had smaller relative standard deviations?RSDs?,indicating that the SVR model had a higher predictive stability.However,the prediction relative errors of the PLSR model for all analysis elements except Na and K were lower than the prediction relative errors given by the SVR model,showing a superior quantitative analysis ability to the SVR model.Through the cross-validation of different quantitative analysis methods,a quantitative analysis model was established for multi-element of soil samples with complex matrix,which optimized the matrix effect in soil quantitative analysis and improved the accuracy of the calibration curve.?4?Research of laser induced breakdown-Raman spectroscopy hybrid instrumentSince mineral materials are crystal structures naturally formed by compounds and individual chemical elements,combining LIBS with Raman to simultaneously acquire the atomic and molecular spectra of a substance is a new method for rapidly detecting homogeneous heterogeneous minerals.In this paper,an integrated LIBS-Raman instrument was developed to detect not only the metal and non-metal elements of a substance,but also the anion group and crystal structure.The instrument adopted a modular design concept,which regulated the mechanical structure and interface type to make it compact and highly integrated.The LIBS optical system and the Raman optical system adopted an orthogonal structure,and the performance parameters of the two methods were optimized,so that the two spectral technologies closely cooperated and did not interfere with each other.The measurement and control system integrated the control mode and data transmission of each component,solving the problem that different components require different interfaces,different control modes and different data transmission channels.In order to further enhance the instrument's automatic operation capability and detection sensitivity,the instrument's versatile sample chamber was equipped with an electric stage and could be filled with shield gas to simulate different environments.The certified samples of calcium carbonate,ammonium persulfate and natural samples of calcite,magnesite,white marble and transparent calcite were detected using the developed instrument,and a good classification result was obtained.The experimental results showed that the instrument could simultaneously obtain the atomic and molecular spectra of the analytical materials,and realize the recognition of the material elements and crystal structures,making it has an unique advantage for the classification of homogeneous heterogeneous materials.