Method for improving quantitative accuracy of LIBS (laser-induced breakdown spectroscopy) based on double-standard-sample multi-spectral-line correction

Abstract

The invention discloses a double-standard-sample multi-spectral-line correction LIBS quantitative accuracy improving method. The method comprises the following steps: acquiring LIBS spectral data of a to-be-detected sample and two standard samples; acquiring multiple pieces of characteristic spectral line data of to-be-detected elements of the to-be-detected sample and the two standard samples from the LIBS spectral data; calculating a spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data; calculating the characteristic spectral line theoretical intensity of the to-be-detected sample according to the spectral line intensity correction factor of the second standard sample; establishing a correction curve according to the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral line of the to-be-detected sample; and calculating the to-be-detected element content of the to-be-detected sample according to the correction curve. By adopting a double-standard-sample multi-spectral-line correction algorithm, the accuracy of quantitative analysis of a single-point multi-spectral-line correction method can be remarkably improved, and meanwhile, the defect that the calculation process of a calibration-free laser-induced breakdown spectroscopy algorithm is tedious is overcome.

Description

Technical Field

[0001] The present invention relates to the field of element quantitative analysis, and in particular to a method for improving LIBS quantitative accuracy by double-standard sample multi-spectral line correction. Background Art

[0002] Laser-induced breakdown spectroscopy (LIBS) is a novel spectroscopic analysis technique developed in recent years. It primarily uses a high-energy pulsed laser focused on the surface of a sample to be tested. This process instantly ablates localized material on the sample, causing it to melt, vaporize, and ionize. This generates a transient plasma that radiates a characteristic spectrum of wavelengths. The characteristic wavelength and intensity of these spectra are then used to identify the elemental species and predict their content. Due to its advantages of rapid, in-situ, and remote analysis, LIBS has been widely used in aerospace, metallurgical analysis, deep space exploration, and other fields. While research on LIBS has deepened with technological advancements, it remains a relatively mature technology. Matrix effects, spectral instabilities, and the detection environment are the main factors limiting its quantitative accuracy, severely hindering the development of this emerging technique. Therefore, developing methods to improve the quantitative accuracy of LIBS is highly valuable.

[0003] Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technology requires no standard samples. Instead, it determines the elemental content of the sample being measured through theoretical calculations, eliminating reliance on standard samples. It has been widely used in fields such as archaeological exploration, alloy analysis, and deep space exploration, where it demonstrates great potential. In recent years, CF-LIBS has evolved into a variety of correction methods to improve the accuracy of quantitative analysis. These methods can be categorized into three main categories: non-stoichiometric ablation correction, self-absorption correction, and single-standard correction. New theoretical approaches have continuously improved the accuracy of LIBS quantitative analysis. However, research has shown that while CF-LIBS variants can significantly improve the accuracy of quantitative analysis, their algorithms are complex and time-consuming, requiring a high level of theoretical knowledge to accurately calculate.

[0004] The single-point multi-line calibration (OP-MLC) method is a rapid LIBS quantitative analysis method that requires only a single standard sample and incorporates some CF-LIBS calculation theory. Compared with traditional CF-LIBS methods, it significantly omits the calculation process, offering advantages such as flexibility and simplicity. However, its relatively low quantitative accuracy has significantly limited its application. Summary of the Invention

[0005] The present invention provides a method for improving the quantitative accuracy of LIBS using dual-standard multi-line correction. This method addresses the problems in the prior art where the algorithm for calibration-free laser-induced breakdown spectroscopy is overly complex and time-consuming, requiring personnel with advanced theoretical knowledge to accurately calculate, and the relatively low quantitative accuracy of the single-point multi-line correction method, which greatly hinders its practical application.

[0006] In one aspect, an embodiment of the present invention provides a method for improving LIBS quantitative accuracy using dual-standard multi-spectral correction, comprising: Obtain LIBS spectral data of the sample to be tested and two standard samples; Acquire multiple characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectrum data; Calculating a spectral line intensity correction factor of a second standard sample based on the characteristic spectral line data; Calculating the theoretical intensity of the characteristic spectral line of the sample to be tested according to the spectral line intensity correction factor of the second standard sample; Establishing a calibration curve based on the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral line of the sample to be tested; The content of the element to be measured in the sample to be measured is calculated according to the calibration curve.

[0007] In one possible implementation, obtaining LIBS spectral data of the sample to be tested and two standard samples includes: Setting two standard samples of the same material with similar composition and a group of initial samples of the same material to be tested; The initial sample to be tested is pre-processed by cutting, grinding and polishing to obtain the cylindrical sample to be tested; LIBS is used to detect different positions of each of the standard samples and the sample to be tested to obtain a plurality of LIBS spectral data.

[0008] In a possible implementation, after obtaining the LIBS spectra of the sample to be tested and the two standard samples, the method further includes: The average value of the plurality of LIBS spectral data of each of the standard sample and the sample to be tested is calculated to obtain the average spectral data of each of the standard sample and the sample to be tested.

[0009] In one possible implementation, obtaining a plurality of characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectral data includes: Performing LIBS on a pure sample of the element to be measured under the same laboratory environment and experimental conditions as those used to obtain the LIBS spectrum data to obtain an element spectrum line corresponding to the element to be measured; A plurality of characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples are obtained from the LIBS spectral data according to the element spectral line.

[0010] In a possible implementation, calculating the spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data includes: Calculating the theoretical spectral line intensity corresponding to the second standard sample based on the spectral line intensity of the first standard sample; The spectral line intensity correction factors of the plurality of characteristic spectral lines of the second standard sample are calculated according to the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of the plurality of characteristic spectral line data of the second standard sample.

[0011] In a possible implementation, establishing a calibration curve according to the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral line of the sample to be tested includes: A calibration curve is established with the actual spectral line intensity of the first standard sample as the abscissa and the theoretical intensities of the plurality of characteristic spectral lines of the sample to be tested as the ordinate.

[0012] The LIBS quantitative accuracy improvement method of the present invention using dual-standard multi-spectral correction has the following advantages: The use of a double-standard multi-spectral line correction algorithm can significantly improve the accuracy of quantitative analysis using the single-point multi-spectral line correction method, while also overcoming the drawback of the cumbersome calculation process of the calibration-free laser-induced breakdown spectroscopy algorithm. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 A flowchart of a method for improving LIBS quantitative accuracy using dual-standard multi-spectral correction provided in an embodiment of the present application; Figure 2 A double standard multi-spectral calibration curve of the Mn element in an embodiment of a method for improving LIBS quantitative accuracy using double standard multi-spectral calibration provided in an embodiment of the present application; Figure 3 A double standard multi-spectral calibration curve of Ni element in an embodiment of a method for improving LIBS quantitative accuracy by double standard multi-spectral calibration provided in an embodiment of the present application; Figure 4A comparison chart of the LIBS quantitative results of the Mn element using single-point multi-spectral line correction and double-standard multi-spectral line correction in an embodiment of a method for improving LIBS quantitative accuracy using double-standard multi-spectral line correction provided in an embodiment of the present application; Figure 5 This is a comparison chart of the LIBS quantitative results of the Ni element using single-point multi-line correction and double-standard multi-line correction in an embodiment of a method for improving LIBS quantitative accuracy using double-standard multi-line correction provided in an embodiment of the present application. DETAILED DESCRIPTION

[0015] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] Figure 1 A schematic flow chart of a method for improving the quantitative accuracy of LIBS using dual-standard multi-spectral correction provided by an embodiment of the present invention; an embodiment of the present invention provides a method for improving the quantitative accuracy of LIBS using dual-standard multi-spectral correction, comprising: Obtain LIBS spectral data of the sample to be tested and two standard samples; Acquire multiple characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectrum data; Calculating a spectral line intensity correction factor of a second standard sample based on the characteristic spectral line data; Calculating the theoretical intensity of the characteristic spectral line of the sample to be tested according to the spectral line intensity correction factor of the second standard sample; Establishing a calibration curve based on the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral line of the sample to be tested; The content of the element to be measured in the sample to be measured is calculated according to the calibration curve.

[0017] The obtaining of LIBS spectral data of the sample to be tested and two standard samples includes: Setting two standard samples of the same material with similar composition and a group of initial samples of the same material to be tested; The initial sample to be tested is pre-processed by cutting, grinding and polishing to obtain the cylindrical sample to be tested; LIBS is used to detect different positions of each of the standard samples and the sample to be tested to obtain a plurality of LIBS spectral data.

[0018] After obtaining the LIBS spectrum data of the sample to be tested and the two standard samples, the method further includes: The average value of the plurality of LIBS spectral data of each of the standard sample and the sample to be tested is calculated to obtain the average spectral data of each of the standard sample and the sample to be tested.

[0019] Acquiring multiple characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectrum data includes: Performing LIBS on a pure sample of the element to be measured under the same laboratory environment and experimental conditions as those used to obtain the LIBS spectrum data to obtain an element spectrum line corresponding to the element to be measured; A plurality of characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples are obtained from the LIBS spectral data according to the element spectral line.

[0020] Calculating the spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data includes: Calculating the theoretical spectral line intensity corresponding to the second standard sample based on the spectral line intensity of the first standard sample; The spectral line intensity correction factors of the plurality of characteristic spectral lines of the second standard sample are calculated according to the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of the plurality of characteristic spectral line data of the second standard sample.

[0021] The establishing of a calibration curve according to the actual spectral line intensity of the first standard sample and the characteristic spectral line theoretical intensity of the sample to be tested comprises: A calibration curve is established with the actual spectral line intensity of the first standard sample as the abscissa and the theoretical intensities of the plurality of characteristic spectral lines of the sample to be tested as the ordinate.

[0022] Exemplarily, two standard samples of the same material with similar composition and a group of initial samples to be tested of the same material are obtained respectively.

[0023] These initial samples were pre-processed, including cutting, grinding, and polishing, to make them cylindrical samples with a radius of 3 cm and a height of 40 cm.

[0024] Under the same experimental environment, these cylindrical samples were tested separately using a laser-induced breakdown spectroscopy system to obtain their respective LIBS spectral data, where multiple LIBS data were collected at different positions for each sample.

[0025] The multiple LIBS data collected at different positions of each sample are set as a group. Each group contains multiple LIBS data. The LIBS data in each group are averaged, that is, an average spectrum data is obtained at each position.

[0026] Under the same experimental environment and conditions, the pure sample of the element to be tested is tested using the laser-induced breakdown spectroscopy system to obtain the corresponding accurate element spectral lines and perform spectral line selection.

[0027] Under the assumptions of local thermodynamic equilibrium and plasma optical thinness, according to the Boltzmann equation, the integrated intensity of the spectrum can be obtained as: (1) in, is the intensity of the emission line at wavelength λ, F is a constant related to the experimental environment and system, C S is the particle content (number fraction), A ki Is spontaneous emission from the energy level k arrive i The transition probability of is the upper energy level degeneracy, U S (T) is the partition function, is the upper energy level, is the Boltzmann constant, T is the plasma temperature.

[0028] For two emission lines of the same element from the same plasma λ 1 and λ 2. The ratio of their spectral line intensities can be described as: (2) in, A ki 、 、 Parameters such as can be found in the database of the National Institute of Standards and Technology (NIST). λ 1 and λ 2 wavelength, we can determine A ki 、 、 are equal parameter values.

[0029] Under certain experimental conditions, it is assumed that the plasma temperature T of the samples to be tested is a constant. Therefore, the right side of formula (2) is equivalent to a constant. For samples of the same material, under given plasma conditions, and Directly proportional.

[0030] Two spectral lines emitted by different samples of the same element and , their intensity ratio can be described as: (3) in, a and b Represents two different samples, is the concentration of the substance in sample a, is the concentration of the substance in sample b.

[0031] When λ1=λ2=λ x When , formula (3) can be rewritten as: (4) Furthermore, for samples of the same material, two standard samples are selected a 、 b There are multiple spectral lines of different wavelengths of a certain element. In the process of selecting such spectral lines, the resonance lines that are easy to self-absorb cannot be selected; then select the standard sample a The actual spectral intensity of each spectral line is: 、 、 、 、 ; The actual spectral intensity of each spectral line in the selected standard sample b is: 、 、 、 、 , the actual spectral intensity of each spectral line in the sample c to be tested is selected as: 、 、 、 、 .

[0032] Select standard sample b For the first calibration standard, select the standard a As the second calibration standard, b The plasma temperature at this moment T As the benchmark, the standard a The theoretical spectral intensity of the selected spectral lines of different wavelengths can be expressed as: (5) in, x The options are 1, 2, 3, ...

[0033] Then select the standard a The wavelength is λ x The actual spectrum and theoretical spectrum The gap between them can be expressed as: (6) Then the multiple spectral line intensity correction factors of each wavelength calculated based on the second calibration standard a can be expressed as: (7) in, x You can choose 1, 2, 3, ... Then the theoretical spectral intensity of each spectral line in the sample c to be tested can be expressed as: (8) Standard sample b The actual spectral line intensity selected from the sample is used as the horizontal axis. c The theoretical spectral line intensity is used as the ordinate to establish a calibration curve, and the slope is K , then formula (4) can be rewritten as: (9) Then the content of a certain element in the sample to be tested is: (10) In a possible embodiment, six standard samples of medium and low alloy steel are used as implementation objects, and Mn and Ni are selected as detection targets respectively. The specific steps are as follows: 1. For two elements, obtain two standard samples of the same material with similar composition and four initial samples to be tested. The record numbers of these six samples are: S1, S2, S3, S4, S5, and S6; 2. Perform preliminary pretreatment on these initial samples, including cutting, grinding, and polishing, to make them cylindrical samples with a radius of 3 cm and a height of 40 cm; 3. Under the same experimental environment, these cylindrical samples were tested separately using a laser-induced breakdown spectroscopy system to obtain their respective LIBS spectral data, where multiple LIBS data were collected at different positions for each sample; 4. Assign multiple LIBS data points collected at different locations of each sample to a group. Each group contains multiple LIBS data points, and average the LIBS data points within each group to obtain an average spectrum data point at each location. 5. Record the first calibration standard sample of the Mn element as S4 and the second calibration standard sample as S5. 6. The first calibration standard sample of Ni element is S3, and the second calibration standard sample is S4; 7. Select different wavelength spectral lines of Mn element, which are: 403.08, 403.31, 403.45, 475.40, 478.34nm; select different wavelength spectral lines of Ni element, which are: 339.30, 346.17, 349.30, 352.45nm; 8. Calculate the theoretical spectral intensity of the spectral lines at different wavelengths according to formula (5); calculate the correction factors of the intensity of multiple spectral lines at each wavelength according to formulas (6) and (7); 9. Calculate the theoretical spectral intensity of each spectral line in the sample to be tested according to formula (8); 10. Establish a calibration curve using the actual spectral line intensity of the first calibration standard sample as the abscissa and the theoretical spectral line intensity of the sample to be tested as the ordinate; 11. Calculate the element content of the sample to be tested according to formula (10).

[0034] The results are as follows Figure 2 、 3 , 4, and 5.

[0035] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including all changes and modifications that fall within the scope of the present invention and the preferred embodiments.

[0036] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction, characterized in that: include: Obtain LIBS spectral data of the sample to be tested and two standard samples; Acquire multiple characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectrum data; Calculating a spectral line intensity correction factor of a second standard sample based on the characteristic spectral line data; Calculating the theoretical intensity of the characteristic spectral line of the sample to be tested according to the spectral line intensity correction factor of the second standard sample; Establishing a calibration curve based on the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral line of the sample to be tested; The content of the element to be measured in the sample to be measured is calculated according to the calibration curve.

2. The method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction according to claim 1, characterized in that: The obtaining of LIBS spectral data of the sample to be tested and two standard samples includes: Setting two standard samples of the same material with similar composition and a group of initial samples of the same material to be tested; The initial sample to be tested is pre-processed by cutting, grinding and polishing to obtain the cylindrical sample to be tested; LIBS is used to detect different positions of each of the standard samples and the sample to be tested to obtain a plurality of LIBS spectral data.

3. The method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction according to claim 1, characterized in that: The obtaining of LIBS spectral data of the sample to be tested and two standard samples includes: The average value of the multiple LIBS spectra of each of the standard sample and the sample to be tested is calculated to obtain the average spectrum data of each of the standard sample and the sample to be tested.

4. The method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction according to claim 1, wherein: Acquiring multiple characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples from the LIBS spectrum data includes: Performing LIBS on a pure sample of the element to be measured under the same laboratory environment and experimental conditions as those used to obtain the LIBS spectrum data to obtain an element spectrum line corresponding to the element to be measured; A plurality of characteristic spectral line data of the element to be measured of the sample to be measured and the two standard samples are obtained from the LIBS spectral data according to the element spectral line.

5. The method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction according to claim 1, characterized in that: Calculating the spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data includes: Calculating the theoretical spectral line intensity corresponding to the second standard sample based on the spectral line intensity of the first standard sample; The spectral line intensity correction factors of the plurality of characteristic spectral lines of the second standard sample are calculated according to the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of the plurality of characteristic spectral line data of the second standard sample.

6. The method for improving LIBS quantitative accuracy by dual-standard multi-spectral correction according to claim 1, characterized in that: The establishing of a calibration curve according to the actual spectral line intensity of the first standard sample and the characteristic spectral line theoretical intensity of the sample to be tested comprises: A calibration curve is established with the actual spectral line intensity of the first standard sample as the abscissa and the theoretical intensities of the plurality of characteristic spectral lines of the sample to be tested as the ordinate.

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