Study Of Quantitative Analysis In Laser-Induced Breakdown Spectroscopy Using Single-Sample Calibration

Laser-induced breakdown spectroscopy(LIBS)is an analytical technique with advantages including fast,real-time,in situ detection,no sample preparation,and multi-elemental analysis.At present,LIBS has been widely applied in many fields,such as industry,agriculture,environmental science,and medicine.Multi-sample calibration is usually used in the quantitative analysis of LIBS.Although this method has high detection accuracy,a series of standard samples are required to establish a calibration curve.The application of multi-sample calibration has great limitations in the field lack of standard samples,such as space exploration,environmental protection,geological survey.In addition,the calibration-free method can achieve quantitative analysis without standard sample but with low detection accuracy.Therefore,a new method called single-sample calibration LIBS(SSC-LIBS)was proposed to achieve accurate quantitative analysis using one standard sample.The major achievements and innovations are as follows:(1)Based on the principle of laser atomic emission spectroscopy,SSC-LIBS is proposed that requires only a single standard sample for calibration.The calculation formula of this method is derived by the Lomakin-Scherbe formula.The element content of the unknown sample can be calculated by just knowing the line intensity of all of the elements in an unknown sample and a standard sample.SSC-LIBS was applied to the quantitative analysis of brass,micro-alloy steel,and nickel-based alloy.Compared with multi-sample calibration,the R~2,RMSECV,ARE,and ARSD of Cu elements were improved from 0.40,3.55 wt.%,5.19%,and16.22%to 0.97,0.76 wt.%,1.05%,and 1.15%,respectively.The results demonstrated that SSC-LIBS can improve the accuracy and stability of detecting major elements.(2)The self-absorption effect,the matrix effect,and the spectral line interference and other factors lead to the poor accuracy of the quantitative analysis of LIBS.Thus,according to the mechanism of self-absorption and matrix effects,the single-sample formula was corrected by introducing the self-absorption coefficient and the total quality of ablation.Based on the revised formula,a single-sample quantitative analysis model for the binary sample was established to simulate the experimental results,and the effects of self-absorption and matrix effects on the accuracy of the model were studied.The simulation results show that for binary samples,the more self-absorption,the lower the model accuracy;the larger the difference between the standard sample and the unknown sample,the lower the model accuracy;the detection accuracy of high content elements is higher.(3)The actual sample generally contains multiple elements while the binary sample model is too idealized.Thus,the single-sample quantitative analysis model is extended from the ternary sample to the multielement sample.The simulation results show that for multielement samples,the effects of self-absorption and matrix effects on quantitative analysis are basically consistent with binary samples.For high content elements,the corresponding matrix content is low,thus the prediction accuracy is higher due to smaller effects of self-absorption and matrix effects.The multielement sample model was verified by quantitative analysis for nickel-based alloys.For trace elements,the average R~2 between the simulated and measured values of element content is 0.96.For the major elements,taking Nb element as an example,the RMSECV between the simulated and measured values is 0.33 wt.%,which is basically equivalent to the RMSECV between the standard and the measured values.In summary,the SSC-LIBS can effectively improve the analysis accuracy of major elements.The effects of self-absorption and matrix effects on the relationship between element content and relative error were studied by a single-sample quantitative analysis model.The model can not only provide guidance for the selection of standard samples but also predict and correct experimental results.The SSC-LIBS provides a more convenient and accurate calibration method for the quantitative analysis of LIBS,which is of great significance for promoting the application of LIBS.