Quantitative analysis method of laser-induced breakdown spectroscopy based on temperature iterative correction of self-absorption effect

Correction of self-absorption effect in laser-induced breakdown spectroscopy based on temperature iteration

The light emitted from plasma created by the interaction of a laser beam with the sample surface is always subject to self-absorption (SA) from its cold outer region. This phenomenon affects the precision and the uncertainty of the quantitative analysis by laser-induced breakdown spectroscopy. To overcome this inherent flaw of spectroscopy, different methods of SA corrections (SACs) have been proposed. In this work laser induced breakdown spectroscopy was performed on a set of metal alloys of reference standard samples and the respective quantitative calibration curves were plotted. The SAC was performed by adopting a method based on the ratio of electron density calculated from Stark broadening of the absorbed line and non-absorbed one emitted by the low concentration element present in the air atmosphere. The quality of the linear relationship between the normalized spectral line intensity and analytic concentration was estimated by the coefficient of determination and the quality coefficient of the regression lines. The validation of this procedure by the measurement of two new standards confirms the improvement of the quantitative analysis using the SAC especially for the single ionized emitted line in laser induced breakdown spectroscopy.

The relative intensity is one of the parameters of the spectral lines that indicate the emission strength of such lines. The spectral lines relative intensity database for most elements has been recorded a long time ago through spectroscopic data obtained by arc, spark, and vacuum tube. The problem is that relative line intensity is source dependent and the current database cannot be used for Laser-Induced Breakdown Spectroscopy (LIBS). Since LIBS is dealing with transient plasma, then a lot of parameters should be studied in order to find suitable conditions and a suitable way to record this database. In this work, we are trying to find a way to construct a database for relative lines intensities that can be used properly in LIBS analysis. The LIBS spectral lines have been recorded for different delay times for different copper alloy samples. Then, some chosen copper’ spectral lines were compared. An empirical formula has been proposed to calculate the spectral line intensity for each delay time. It was found that for delay times between 1000 ns and 2000 ns the spectral lines were related together in a way that the copper concentration doesn’t affect the spectral line relative intensity but it only affects the value of the spectral line intensity.

Effect of plasma radiation attenuation rate on the uncertainty of LIBS signal and real-time correction method.

Impact of microstructural properties on hardness of tungsten heavy alloy evaluated by stand-off LIBS after PSI plasma irradiation

With the rapid development of spectroscopy technology, laser induced breakdown spectroscopy (LIBS) has become the focus of elemental analysis technology in recent years. With its advantages of non-destructive testing, rapid and multi-element detection, LIBS has been successfully applied to the analysis of geochemical characteristics of soil elements in river basins. The application of LIBS technology in soil elemental analysis of watershed is reviewed in detail. The accuracy of LIBS technology in soil element analysis is studied with the Masha River Basin as the research area. On this basis, the key problems in the process of soil element analysis, such as spectral enhancement methods and quantitative analysis methods, were analyzed. The analysis results show that the accuracy of elemental analysis between LIBS and traditional chemical methods is not much different, but the analysis time of LIBS method is shorter. Methods such as MLR, PLSR, and internal standard methods can improve the fit of the calibration curve and reduce the quantitative analysis error. By changing parameters such as laser energy and delay time, the spectral intensity can be enhanced to reduce the effects of matrix effects. In the process of elemental analysis, the effects of soil physical and chemical parameters should be considered comprehensively, and appropriate quantitative analysis methods should be adopted to improve the accuracy of the analysis results.

In this paper, laser-induced breakdown spectroscopy (LIBS) technique is used for concentration prediction of six elements of Mn, Si, Cu, Fe, Zn, and Mg in seven Al samples by two approaches of artificial neural network (ANN) and standard calibration curve. ANN is utilized as a new technique for determination and classification of various materials and elements in LIBS method. In this study, a few spectra of six aluminum standards with known concentrations are used for training of ANN. It should be noted that the mentioned network is not on trial and error basis, but it is a self-organized network. Calibration curve method, which is implemented in represented paper, determines certain relation between concentration and intensity. Then, the calibration curve and ANN methods obtained by six samples are used for prediction of the elements of the seventh standard sample in order to check the accuracy of these methods and make a comparison. In both approaches, a self-absorption correction is applied for high concentrations species and an improvement in prediction of two methods is seen. Results illustrate that at high concentrations except for Si, ANN shows a better prediction with a lower relative error compared to calibration curve approach after self-absorption correction. Primitive study without any self-absorption correction shows that ANN and calibration curve predictions with the best result are related to Fe with R 2 = 0.99 % having the minimum errors.

Correction of self-absorption effect in calibration-free laser-induced breakdown spectroscopy(CF-LIBS) by considering plasma temperature and electron density

In a laser-induced breakdown spectroscopy (LIBS) system that performs elemental analysis of a target by acquiring the emission of plasma generated on the material surface by a focused laser, the plasma signal may be affected by the flow of the surrounding gas. A flow of gas may be present when LIBS measurements are performed in a special environment where an inert gas is normally applied. In such an environment, the flow of gas may affect the intensity of emission generated in plasma. The LIBS spectral intensity in the gas flow field changes according to the direction of the gas flow and the signal detector of the LIBS. In this case, the correlation between the flow rate and intensity of the spectral line can be confirmed both theoretically and experimentally. In this study, changes in the signal according to the flow rate were theoretically evaluated using the view factor and wave equation. In addition, LIBS signals were examined based on the flow of Ar, N2, and He gases in the experiment. The experimental results confirmed the range of effective gas flow rates over which the correlation between the flow rate and intensity of the LIBS spectral line could be inferred. These results could be used for calibration to achieve accurate measurement of LIBS signals in gas flow fields. In addition, this analysis has the potential to shed light on the properties of flowing gases that affect plasma by reversibly tracking changes in the signal of LIBS in a confined environment.

We quantitatively analyze the concentration of element chromium in edible gelatin sample by the laser-induced breakdown spectroscopy. As the excitation source, Nd:YAG pulsed laser (wavelength 355 nm) is used to generate a laser plasma in edible gelatin. We study the relationship between spectral intensity and delay time, and find that the optimal condition is 1.7 μs. The experimental data show that the relation between the spectral line intensity (CrI: 425.43 nm) and the concentration of chromium is linear when we use the internal standard method to quantitatively analyze the concentration of chromium in a range from 10 ppm to 200 ppm. This study shows that internal standard method of quantitative analysis works well on measuring the chromium concentration in edible gelatin.

Laser-induced breakdown spectroscopy (LIBS) has been employed for the qualitative and quantitative analysis of quartz-bearing limestone using two different calibration-free LIBS methods, that is, one-line calibration-free LIBS (OLCF-LIBS) and self-calibration LIBS (SC-LIBS) methods in conjunction with energy-dispersive x-ray spectroscopy (EDS) and x-ray fluorescence spectroscopy (XRF). The plasma is generated by focusing a Q-switched Nd:YAG laser (1064nm, 134mJ pulse energy, 9ns pulse duration) in air under atmospheric pressure. Spectral analysis revealed the presence of Ca, Si, and Mg. Plasma temperature is deduced using the neutral spectral lines of pertinent elements using the Boltzmann plot method, and an average value of 3462K is used for the quantitative analysis. An average value for electron number density is calculated as (1.3±0.3)×1017 cm-3 from the Stark broadening of isolated neutral Ca, Si, and Mg lines and a singly ionized Ca line. The elemental composition determined by different LIBS methods and other traditional analytical techniques are OLCF-LIBS (Ca, 71.82%; Si, 28.12%; Mg, 0.048%), SC-LIBS (Ca, 69.19%; Si, 28.92%; Mg, 1.87%), EDS (Ca, 68.86%; Si, 30.12%; Mg, 0.32%), and XRF (Ca, 68.62%; Si, 27.18%; Mg, 1.56%). By comparing the results of both CF-LIBS methods along with EDS and XRF, it is demonstrated that the SC-LIBS method is more appropriate than the OLCF-LIBS and gives compositions comparable with that determined by EDS and XRF and, hence, displays its ability as a powerful tool for the compositional analysis of complex minerals.

We report a highly sensitive electrolytic copper (Cu) detection method using nanoparticle enhanced laser-induced breakdown spectroscopy (NELIBS) for metal smelting processes. The sulfate solution Cu with content ranging from 10 to 50 g/L was prepared and measured on the nanoparticle chip. The experimental results showed that the Cu spectral line intensity of NELIBS increased 5.5 to 9.4 times compared with typical LIBS without nanoparticles. The calibration curve was established based on the spectral line intensity at Cu I 327.40 nm according to the different Cu content in the solution. The determination coefficient R2 of the calibration curve was 0.99. The method of laser-induced breakdown spectroscopy based on drying liquid droplets on the nanoparticle chip can be applied to the rapid determination of Cu content in the copper electrolyte.

Investigation on the dynamic characteristics of LIBS for heavy metal Mn in liquid matrix

Correction of self-absorption effect in calibration-free laser-induced breakdown spectroscopy (CF-LIBS) with blackbody radiation reference

В работе предлагается концепция построения спектроскопической системы на базе эмиссионной и лазерно-искровой эмиссионной спектрометрии, позволяющей выполнять многопараметрический контроль процессов горения на основе измерения множества заранее установленных спектроскопических информативных параметров. Приводятся результаты экспериментального исследования параметров, характеризующие процесс горения пропана. Даётся математическое описание многопараметрического контроля, позволяющее установить допускаемые значения результатов спектральных измерений, обеспечивающие заданную достоверность проводимого контроля. Приводятся результаты компьютерного моделирования допускаемых значений и вероятностей ошибок контроля и их сравнение с результатами эксперимента. Introduction. Combustion processes are characterized by multiple informative parameters, including spectroscopic ones. Therefore, in the research, to solve the monitoring problem, there is proposed to use the methods of applied optical spectrometry, where a monitoring system built on the basis of optical spectrometers measures optical radiation carrying spectroscopic data on the monitored process and can replace most of the monitoring and measuring equipment placed on the object. The gathered spectroscopic data allows one to carry out multi-parameter monitoring, where the conclusion about the state of the monitored process is performed based on the comparison and analysis of many spectroscopic parameters - separate spectral lines and / or spectral regions, as well as their relationship. The aimof the research is to propose a concept of a spectroscopic system that allows one to perform multi-parameter monitoring of combustion processes based on emission and laser-induced breakdown spectroscopy (LIBS) with a given monitoring reliability. Findings. 1) An experimental study of the spectroscopic informative parameters characterizing the propane combustion process was carried out by the methods of emission and laser-induced breakdown spectroscopy; the most intense spectral lines and areas characterizing the combustion process of gaseous hydrocarbon fuel were identified, and their dependence on the gas / air ratio was given. By measuring the values of the intensity of these lines and taking into account their relationship, it is feasible to implement multi-parameter monitoring of the combustion process; 2) The concept of designing a spectroscopic system based on emission and laser-induced breakdown spectroscopy was proposed, which allows to carry out multi-parameter monitoring of combustion processes based on the measurement of pre-defined spectroscopic informative parameters; 3) There was derived a mathematical apparatus that allowed to establish the limit values ​​of the results of spectral measurements, which ensure the specified requirements for the probabilities of monitoring errors of the 1st and 2nd kind. 4) Computer simulation of the permissible values ​​and error probabilities for the case of monitoring 4 parameters was carried out. Numerical findings were compared with the experimental results. It was found that the emission method exhibits the probability of an error of the 1st kind of 17.1%, and of the 2nd kind of 12.3%, while the theoretical value aS= 14.9 % at bдоп = 10 %. The LIBS method showed the probability of an error of the 1st kind of 16.1%, and of the 2nd kind of 11.7%. The best performance of monitoring was found in the case of applying two methods of spectroscopy. The probability of an error of the 1st kind was 15.5%, and the 2nd kind was 10.8%. This can be explained by the fact that the most intense spectral bands or lines were chosen as the monitored parameters.