Element quantitative analysis method based on laser-induced breakdown spectroscopy

Abstract

The present application relates to the technical field of laser-induced breakdown spectroscopy, in particular to a kind of element quantitative analysis method based on laser-induced breakdown spectroscopy, it includes the following steps: input element needing to draw Saha-Boltzmann graph;Read the corresponding element atomic and ion information matched;Plasma temperature is preset;Update plasma temperature, draw Saha-Boltzmann graph;Plasma temperature is calculated using Saha-Boltzmann graph curve;Judge whether the calculated plasma temperature is close to the preset plasma temperature;Partition function is calculated, and each component concentration is obtained using CF method.The present application is ingenious in design, improves work efficiency;Read spectrum, remove background noise, calibrate spectral intensity, find peak corresponding spectral line, calculate partition function, obtain each component concentration;Greatly reduce the amount of calculation, reduce the possibility of human error;It is favorable to improve the accuracy of quantitative analysis.

Description

Technical Field

[0001] This invention relates to the field of laser-induced breakdown spectroscopy, and in particular to a method for quantitative elemental analysis based on laser-induced breakdown spectroscopy. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is a widely used technique for elemental analysis of solid samples and remains a cutting-edge research area in analytical science. LIBS offers advantages such as eliminating the need for complex sample preparation, high analysis speed, real-time online or remote analysis capabilities, and the ability to analyze samples of any form and any element. Consequently, it has found widespread application in fields including materials science, biomedicine, agriculture, environmental science, archaeology, and space exploration. In 1999, Ciucci et al. proposed free-calibration laser-induced breakdown spectroscopy (CF-LIBS), which utilizes the detected atomic spectra to achieve quantitative elemental analysis of individual samples. Subsequently, in 2007, Tognoni et al. improved CF-LIBS by adding the use of ionic spectra, significantly enhancing analytical accuracy. Since then, CF-LIBS has been widely adopted. However, processing sample spectra is an extremely complex process involving extensive computation. Manual calculations from start to finish are time-consuming, and the computational load increases exponentially with the number of elements being identified, greatly increasing the probability of errors. Summary of the Invention

[0003] This invention addresses the problems of existing technologies by providing a method for quantitative elemental analysis based on laser-induced breakdown spectroscopy. The method is ingeniously designed and incorporates all the necessary procedures for spectral analysis, significantly improving work efficiency. It involves reading the spectrum, removing background noise, calibrating spectral intensity, identifying peak-corresponding spectral lines, plotting the Saha-Boltzmann curve, calculating the partition function, and obtaining the concentration of each component. This greatly reduces the computational load and the possibility of human error. Furthermore, spectral line intensity calibration provides more accurate spectral line intensities, which is beneficial for improving the accuracy of quantitative analysis.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention provides a method for quantitative elemental analysis based on laser-induced breakdown spectroscopy, comprising the following steps:

[0006] S1. Input the elements for which you want to plot the Saha-Boltzmann diagram;

[0007] S2. Determine whether the corresponding element atom and ion information to be matched already exists. If not, read the spectral file and generate the corresponding element atom and ion information; if they exist, proceed to step S3.

[0008] S3. Read the matched corresponding element atom and ion information;

[0009] S4, Preset plasma temperature;

[0010] S5. Update the plasma temperature and plot the Saha-Boltzmann diagram;

[0011] S6. Fit the Saha-Boltzmann plot;

[0012] S7. Calculate the plasma temperature using the Saha-Boltzmann plot curve;

[0013] S8. Determine whether the calculated plasma temperature is close to the preset plasma temperature. If not, proceed to step S5; if yes, proceed to step S9.

[0014] S9. Calculate the partition function and use the CF method to obtain the concentration of each component;

[0015] S10, End.

[0016] In step S2, the method for reading the spectral file and generating corresponding elemental atom and ion information includes the following steps:

[0017] S21. Read the spectral file;

[0018] S22. Perform median filtering and save the filtered file;

[0019] S23. Determine if there are any files for points that need to be calibrated. If so, proceed to step S24.

[0020] S24. Read the file of the points that need to be calibrated;

[0021] S25, Read the next point;

[0022] S26. Using the filtered file, extract the points on both sides of the center point wavelength;

[0023] S27. Determine whether the spectral line intensity of the point closer to the center point is greater. If yes, proceed to step S28; otherwise, proceed to step S29.

[0024] S28, Substitute into the formula Calculate the fitted values, assign them to the center points, and update the filtered file.

[0025] S29. Determine if there are any uncalibrated points remaining in the file. If yes, proceed to step S25; otherwise, proceed to step S30.

[0026] S30. Find the peak value and generate the corresponding element atom and ion information.

[0027] In step S28, when the wavelengths and spectral intensities corresponding to the left and right sides of calibration point x are x1, x2, y1, and y2 respectively, the spectral intensity of calibration point x can be calculated as follows:

[0028]

[0029] In steps S8 and S9, the method for calculating the partition function is as follows: the partition function Us(T) will be calculated using the F-value in the CF method. The F-value is calculated using the normalization method, that is, the concentrations of all elements are added together to get 1. The formula is as follows:

[0030]

[0031] Where qs is the intercept of the fitted slope, the F value is obtained by solving the above formula, and the concentration of each component can be theoretically calculated, as shown in the following formula:

[0032]

[0033] In step S7, the method for calculating the plasma temperature using the Saha curve is as follows: based on the preset plasma temperature, calculate the points on the Saha-Boltzmann plane corresponding to each spectral line; the calculation formula is as follows:

[0034]

[0035]

[0036] In the above formula, m e For electron mass, k B Where n is Boltzmann's constant, h is Planck's constant, and n is Boltzmann's constant. e Electron density;

[0037] The Saha-Boltzmann slope is fitted by points on the obtained plane. The slope of this slope can be used to calculate the plasma temperature. By comparing the calculated plasma temperature with the preset plasma temperature, the actual plasma temperature is calculated iteratively step by step.

[0038] The beneficial effects of this invention are:

[0039] This invention is ingeniously designed, incorporating all the necessary procedures for spectral analysis, greatly improving work efficiency. It reads the spectrum, removes background noise, calibrates spectral intensity, locates the peak corresponding spectral line, plots the Saha-Boltzmann curve, calculates the partition function, and obtains the concentration of each component. This significantly reduces the computational load and the possibility of human error. Furthermore, spectral line intensity calibration provides more accurate spectral line intensities, which is beneficial for improving the accuracy of quantitative analysis. Attached Figure Description

[0040] Figure 1 This is a flowchart of a method for quantitative elemental analysis based on laser-induced breakdown spectroscopy according to the present invention.

[0041] Figure 2 This is the spectrum of the continuous background noise with a maximum value of 2000 and a sampling window size of 49 in this embodiment.

[0042] Figure 3 This is a schematic diagram of the Saha-Boltzmann diagonal line in this embodiment. Detailed Implementation

[0043] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. The present invention will be described in detail below with reference to the accompanying drawings.

[0044] A quantitative elemental analysis method based on laser-induced breakdown spectroscopy, such as Figure 1 As shown, it includes the following steps:

[0045] S1. Input the elements for which you want to plot the Saha-Boltzmann diagram;

[0046] S2. Determine whether the corresponding element atom and ion information to be matched already exists. If not, read the spectral file and generate the corresponding element atom and ion information; if they exist, proceed to step S3.

[0047] S3. Read the matched corresponding element atom and ion information;

[0048] S4, Preset plasma temperature;

[0049] S5. Update the plasma temperature and plot the Saha-Boltzmann diagram;

[0050] S6. Fit the Saha-Boltzmann plot;

[0051] S7. Calculate the plasma temperature using the Saha-Boltzmann plot; the method for calculating the plasma temperature using the Saha plot is as follows: based on the preset plasma temperature, calculate the points on the Saha-Boltzmann plane corresponding to each spectral line; the calculation formula is as follows:

[0052]

[0053]

[0054] In the above formula, the degeneracy g of the k-level is... k A is the transition probability, E is the energy level, I is the relative spectral intensity, and m is the energy level. e For electron mass, k B Where n is Boltzmann's constant, h is Planck's constant, and n is Boltzmann's constant. e Electron density;

[0055] The Saha-Boltzmann oblique line is fitted by the points on the obtained plane, such as... Figure 3 As shown, the slope of the line can be used to calculate the plasma temperature. By comparing the calculated plasma temperature with the preset plasma temperature, the actual plasma temperature can be calculated iteratively step by step.

[0056] S8. Determine whether the calculated plasma temperature is close to the preset plasma temperature. If not, proceed to step S5; if yes, proceed to step S9.

[0057] S9. Calculate the partition function and use the CF method to obtain the concentration of each component. The method for calculating the partition function is as follows: the partition function Us(T) will be obtained by solving for the F value in the CF method. The F value is obtained by normalization, that is, the concentrations of all elements are added together to get 1. The formula is as follows:

[0058]

[0059] Where qs is the intercept of the fitted slope, the F value is obtained by solving the above formula, and the concentration of each component can be theoretically calculated, as shown in the following formula:

[0060]

[0061] S10, End.

[0062] Specifically, this invention is ingeniously designed, incorporating all the necessary procedures for spectral analysis, greatly improving work efficiency; it reads the spectrum, removes background noise, calibrates spectral intensity, finds the spectral lines corresponding to the peaks, plots the Saha-Boltzmann curve, calculates the partition function, and obtains the concentration of each component; it greatly reduces the amount of calculation and lowers the possibility of human error; it adds a debugging function, as some spectral lines may be incorrectly identified due to matrix effects or self-absorption effects, therefore the design prevents automatic updates based on spectral data when the corresponding element atom and ion information file already exists.

[0063] In this embodiment, the method for reading the spectral file and generating corresponding elemental atom and ion information in step S2 includes the following steps:

[0064] S21. Use a spectrometer to read the spectral file; the spectrum measured by the spectrometer contains two pieces of information, namely the wavelength and the spectral intensity corresponding to the wavelength (i.e., spectral line intensity);

[0065] S22. Perform median filtering and save the filtered file. Median filtering is a nonlinear signal processing technique based on order statistics theory that can effectively suppress noise. The basic principle of median filtering is to replace the value of a point in a digital image or digital sequence with the median value of all points in its neighborhood, making the surrounding pixel values ​​closer to the true value, thereby eliminating isolated noise points. This part requires setting two parameters: the maximum noise value and the sampling window size. The maximum noise value is set based on the continuous background noise in the measured spectrum; the greater the continuous background noise in the spectrum, the larger this value. The sampling window size varies depending on the sample being measured; it is often smaller when there are many types of elements in the sample and larger when there are fewer types of elements in the sample. Figure 2 The image shown is a spectrum with the maximum continuous background noise value set to 2000 and the sampling window size set to 49; the bottom line represents the noise to be filtered out.

[0066] S23. Determine if there are any files for points that need to be calibrated. If so, proceed to step S24.

[0067] S24. Read the file of the points that need to be calibrated (hereinafter referred to as center points);

[0068] S25, Read the next point;

[0069] S26. Using the filtered file, extract the points on both sides of the center point wavelength;

[0070] S27. Determine whether the spectral line intensity of the point closer to the center point is greater. If yes, proceed to step S28; otherwise, proceed to step S29.

[0071] S28. The calibration module works after the initial identification and determination of spectral line positions. Since the spectrometer measures discrete points, the actual spectral peaks fall within a range of two points; that is, the peak value is always greater than or equal to the measured value between the two points. The spectral line shape of the actual spectrum can be reconstructed using Gaussian fitting; therefore, a first-order Gaussian fitting method can be used for calibration. The formula is: This formula is a first-order Gaussian function, where a, b, and c are all constants, and e is a mathematical constant, representing the base of the natural logarithm. The fitted value is assigned to the center point and updated in the filtered file. Specifically, when the wavelengths and spectral intensities corresponding to the left and right sides of calibration point x are x1, x2, y1, and y2 respectively, the spectral intensity of calibration point x can be calculated as follows:

[0072] S29. Determine if there are any uncalibrated points remaining in the file. If yes, proceed to step S25; otherwise, proceed to step S30.

[0073] S30. Find peaks and compare them with the NIST database corresponding to the input elements to generate corresponding atomic and ion information. This part uses the built-in MATLAB peak-finding function `findpeaks`, which requires setting the minimum peak intensity and the minimum distance between two peaks. For the minimum peak intensity, since noise reduction has already been performed, the minimum peak intensity can be set relatively small, allowing for the identification of more spectral lines. The minimum distance between two peaks depends on the element being measured; the denser the theoretical spectral lines of the element being measured, the smaller the minimum distance between the two peaks should be. After finding the peaks in the spectrum, spectral analysis is required. Line identification requires recognizing the elemental information corresponding to the spectral line. Here, an allowable error value needs to be set; this value depends on the measured spectral data and is generally the maximum value between two nearest neighbors, also known as the spectrometer's resolution. NIST is the abbreviation for the National Institute of Standards and Technology in the United States. NIST conducts basic and applied research in physics, biology, and engineering, as well as research in measurement techniques and testing methods, providing standards, standard reference data, and related services. In this case, it is necessary to extract the atomic lines, ionic lines, and their corresponding transition probabilities A and degeneracy g of the k-level of the element being measured from the NIST database beforehand. k Information such as energy level E and relative spectral intensity I.

[0074] Specifically, under the above settings, the spectral line intensity calibration module uses a first-order Gaussian fitting method to calibrate the spectral line intensity, obtaining more accurate spectral line intensity, which is beneficial to improving the accuracy of quantitative analysis.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the present invention without departing from the scope of the present invention are within the scope of the present invention.

Claims

1. A method for elemental quantitative analysis based on laser-induced breakdown spectroscopy, characterized by, The method comprises the following steps: S1, inputting elements needing to draw Saha-Boltzmann graph; S2, judging whether the corresponding element atomic and ion information needing to be matched exist or not, if not, reading a spectrum file to generate the corresponding element atomic and ion information; if yes, proceeding to step S3; S3, reading the corresponding element atomic and ion information which has been matched; S4, presetting plasma temperature; S5, updating plasma temperature and drawing Saha-Boltzmann graph; S6, fitting Saha-Boltzmann graph; S7, calculating plasma temperature by using Saha-Boltzmann graph curve; S8, judging whether the calculated plasma temperature is close to the preset plasma temperature or not, if not, executing step S5; if yes, executing step S9; S9, calculating partition function and obtaining the concentration of each component by using CF method; S10, ending.

2. The method according to claim 1, wherein, In step S2, the method for reading a spectrum file to generate corresponding element atomic and ion information comprises the following steps: S21, reading a spectrum file; S22, performing median filtering and saving the filtered file; S23, judging whether there is a file of points needing to be calibrated or not, if yes, executing step S24; S24, reading the file of points needing to be calibrated; S25, reading the next point; S26, using the filtered file to extract points on both sides of the center point wavelength; S27, judging whether the spectral line intensity of the point close to the center point is greater or not, if yes, executing step S28, if not, executing step S29; S28, substitute the formula The calculation results in a fit value assigned to the center point and updated into the filtered file; S29, judging whether there is still a point needing to be calibrated in the file or not, if yes, executing step S25, if not, executing step S30; S30, finding a peak value to generate corresponding element atomic and ion information.

3. The method according to claim 2, wherein the method is characterized by, When the wavelengths and spectral intensities corresponding to the left and right sides of the calibration point x are x1, x2, y1 and y2 respectively, the spectral intensity of the calibration point x can be calculated as:

4. The method according to claim 1, wherein, In step S8 and step S9, the method for calculating partition function is that the partition function Us(T) will use the solving of F value in CF method, and the solving of F value uses normalization method, that is, the sum of the concentrations of all elements is 1, and the formula is as follows: Wherein, qs is the intercept of the fitted straight line, the F value is solved by the above formula, the concentration of each component can be theoretically calculated, and the formula is as follows:

5. The method according to claim 1, wherein, In step S7, the method for calculating plasma temperature by using Saha curve is that according to the preset plasma temperature, the points on the Saha-Boltzmann plane corresponding to each spectral line are calculated, and the calculation formula is as follows: In the above formula, m e is the electron mass, k B is the Boltzmann constant, h is the Planck constant, n e is the electron density; The Saha-Boltzmann straight line is fitted by the obtained points on the plane, the slope of the straight line can calculate the plasma temperature, and by comparing the calculated plasma temperature with the preset plasma temperature, the actual plasma temperature is gradually iteratively calculated.

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