A dual-standard multi-line correction method for improving the quantitative accuracy of LIBS

Abstract

The application discloses a kind of double standard sample multispectral line correction LIBS quantitative accuracy promotion method, comprising: obtaining the LIBS spectral data of sample to be measured and two standard samples;From the LIBS spectral data, obtain the multiple characteristic spectral line data of the element to be measured of sample to be measured and two standard samples;According to characteristic spectral line data, the spectral line intensity correction factor of second standard sample is calculated;According to the spectral line intensity correction factor of second standard sample, the characteristic spectral line theoretical intensity of sample to be measured is calculated;According to the actual spectral line intensity of first standard sample and the characteristic spectral line theoretical intensity of sample to be measured, correction curve is established;According to correction curve, the content of element to be measured of sample to be measured is calculated.The application can significantly improve the accuracy of quantitative analysis of single-point multispectral line correction method by using double standard sample multispectral line correction algorithm, and make up the defect that the calculation process of calibration-free laser-induced breakdown spectroscopy algorithm is complicated.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of element quantitative analysis, in particular to a LIBS quantitative accuracy improvement method based on double standard sample and multi-spectral line correction. BACKGROUND

[0002] Laser-induced breakdown spectroscopy (LIBS) is a new type of spectral analysis technology developed in recent years. This technology mainly focuses high-energy pulsed laser on the surface of the sample to be measured. The local material of the sample surface is instantaneously ablated, melted, vaporized and ionized. Then, a transient plasma is generated, which radiates characteristic spectra of certain wavelengths. According to the characteristic wavelengths and intensities of these spectra, the types of elements in the sample can be identified and the content can be predicted. Due to its advantages of rapidity, in-situ analysis, and remote analysis, LIBS is widely used in aerospace, metallurgical analysis, deep space exploration and other fields. With the progress of science and technology, the research of LIBS technology is more in-depth, but it is still not fully mature. Matrix effect, spectral instability, detection environment and other factors are the main reasons for the limitation of quantitative accuracy, which seriously hinders the development of this emerging detection technology. Therefore, it is very meaningful to study a method for improving the quantitative accuracy of LIBS.

[0003] Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) technology does not require standard samples. The element content in the sample to be measured is calculated by a certain theory, which avoids the dependence on standard samples. CF-LIBS is widely used in archaeological detection, alloy analysis and deep space exploration, and has shown great potential in these fields. In recent years, CF-LIBS technology has evolved into various correction methods to improve the accuracy of quantitative analysis. These methods can be divided into three categories: non-chemical stoichiometric ablation correction, self-absorption correction, and single standard sample correction. By proposing new theoretical methods, the accuracy of LIBS quantitative analysis is continuously improved. However, research shows that although CF-LIBS variants can greatly improve the accuracy of quantitative analysis, their algorithms are too complex and time-consuming, and require detection personnel with high theoretical knowledge to accurately calculate.

[0004] The single-point multi-spectral line correction (OP-MLC) method is a LIBS rapid quantitative analysis method that only requires one standard sample and combines part of the CF-LIBS calculation theory. At the same time, compared with traditional CF-LIBS methods, the calculation process is greatly simplified, and the method has the advantages of flexibility and simplicity. However, the quantitative accuracy of this method is relatively low, which greatly hinders the application of this method. SUMMARY

[0005] The embodiment of the present application provides a LIBS quantitative accuracy improvement method of double-standard multi-spectral line correction, to solve the problems that the algorithm of the existing technology of the calibration-free laser-induced breakdown spectroscopy is too complex and time-consuming, and the detection personnel with high theoretical knowledge are needed to accurately calculate, and the quantitative accuracy of the single-point multi-spectral line correction method is relatively low, and the practical application is greatly inhibited.

[0006] In one aspect, the embodiment of the present application provides a LIBS quantitative accuracy improvement method of double-standard multi-spectral line correction, comprising:

[0007] Obtaining LIBS spectrum data of a to-be-detected sample and two standard samples;

[0008] Obtaining a plurality of characteristic spectral line data of a to-be-detected element of the to-be-detected sample and the two standard samples from the LIBS spectrum data;

[0009] Calculating a spectral line intensity correction factor of a second standard sample according to the characteristic spectral line data;

[0010] Calculating a characteristic spectral line theoretical intensity of the to-be-detected sample according to the spectral line intensity correction factor of the second standard sample;

[0011] Establishing a correction curve according to the actual spectral line intensity of the first standard sample and the characteristic spectral line theoretical intensity of the to-be-detected sample;

[0012] Calculating the content of the to-be-detected element of the to-be-detected sample according to the correction curve.

[0013] In one possible implementation, the obtaining of the LIBS spectrum data of the to-be-detected sample and the two standard samples comprises:

[0014] Setting the two standard samples of the same material with similar components and a group of to-be-detected initial samples of the same material;

[0015] Cutting, grinding and polishing the to-be-detected initial samples to obtain the to-be-detected samples in a cylindrical shape;

[0016] Detecting different positions of each of the standard samples and the to-be-detected samples by LIBS to obtain a plurality of LIBS spectrum data.

[0017] In one possible implementation, after the obtaining of the LIBS spectrum data of the to-be-detected sample and the two standard samples, the method further comprises:

[0018] Calculating the average value of a plurality of the LIBS spectrum data of each of the standard samples and the to-be-detected sample to obtain the average spectrum data of each of the standard samples and the to-be-detected sample.

[0019] In a possible implementation, the acquiring the multiple characteristic spectral line data of the to-be-tested element of the to-be-tested sample and the two standard samples from the LIBS spectral data comprises:

[0020] The LIBS inspection of the pure sample of the to-be-tested element under the same laboratory environment and experimental conditions as the acquiring of the LIBS spectral data obtains an element spectrum corresponding to the to-be-tested element;

[0021] The multiple characteristic spectral line data of the to-be-tested element of the to-be-tested sample and the two standard samples are obtained according to the element spectrum.

[0022] In a possible implementation, the calculating the spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data comprises:

[0023] The theoretical spectral line intensity corresponding to the second standard sample is calculated based on the spectral line intensity of the first standard sample;

[0024] The spectral line intensity correction factor of the multiple characteristic spectral lines of the second standard sample is calculated according to the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of the multiple characteristic spectral line data of the second standard sample.

[0025] In a possible implementation, the establishing a correction curve according to the actual spectral line intensity of the first standard sample and the characteristic spectral line theoretical intensity of the to-be-tested sample comprises:

[0026] The correction curve is established with the actual spectral line intensity of the first standard sample as the abscissa and the multiple characteristic spectral line theoretical intensity of the to-be-tested sample as the ordinate.

[0027] The LIBS quantitative accuracy improvement method of the double-standard-sample multi-spectral line correction in the application has the following advantages:

[0028] The double-standard-sample multi-spectral line correction algorithm can significantly improve the quantitative analysis accuracy of the single-point multi-spectral line correction method, and at the same time, make up for the defect of the complicated calculation process of the calibration-free laser-induced breakdown spectroscopy algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0030] Figure 1A flowchart of a double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for an embodiment of the present application;

[0031] Figure 2 A double-standard multi-spectral line correction curve graph of the Mn element in an embodiment of the double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for the present application;

[0032] Figure 3 A double-standard multi-spectral line correction curve graph of the Ni element in an embodiment of the double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for the present application;

[0033] Figure 4 A LIBS quantitative result comparison graph of single-point multi-spectral line correction and double-standard multi-spectral line correction of the Mn element in an embodiment of the double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for the present application;

[0034] Figure 5 A LIBS quantitative result comparison graph of single-point multi-spectral line correction and double-standard multi-spectral line correction of the Ni element in an embodiment of the double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0036] Figure 1 A flowchart of a double-standard multi-spectral line correction LIBS quantitative accuracy improvement method provided for an embodiment of the present application; the present application provides a double-standard multi-spectral line correction LIBS quantitative accuracy improvement method, which comprises:

[0037] acquiring LIBS spectral data of a to-be-measured sample and two standard samples;

[0038] acquiring, from the LIBS spectral data, multi-feature spectral line data of a to-be-measured element of the to-be-measured sample and the two standard samples;

[0039] calculating a spectral line intensity correction factor of a second standard sample according to the feature spectral line data;

[0040] calculating a feature spectral line theoretical intensity of the to-be-measured sample according to the spectral line intensity correction factor of the second standard sample;

[0041] 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 sample to be measured;

[0042] calculating the content of the element to be measured of the sample to be measured according to the correction curve.

[0043] The LIBS spectral data of the sample to be measured and the two standard samples includes:

[0044] Setting the standard samples of the same material with similar components and a group of initial samples to be measured of the same material;

[0045] Cutting, grinding and polishing the initial samples to be measured to obtain the cylindrical samples to be measured;

[0046] Detecting different positions of each of the standard samples and the sample to be measured by LIBS to obtain a plurality of LIBS spectral data.

[0047] After obtaining the LIBS spectral data of the sample to be measured and the two standard samples, it further includes:

[0048] Calculating the average value of a plurality of LIBS spectral data of each of the standard samples and the sample to be measured to obtain the average spectral data of each of the standard samples and the sample to be measured.

[0049] 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:

[0050] Performing LIBS inspection on the pure sample of the element to be measured under the same laboratory environment and experimental conditions as obtaining the LIBS spectral data to obtain the element spectrum corresponding to the element to be measured;

[0051] 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 according to the element spectrum.

[0052] Calculating the spectral line intensity correction factor of the second standard sample according to the characteristic spectral line data includes:

[0053] Calculating the theoretical spectral line intensity corresponding to the second standard sample based on the spectral line intensity of the first standard sample;

[0054] Calculating the spectral line intensity correction factor of a plurality of characteristic spectral lines of the second standard sample according to the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of a plurality of characteristic spectral line data of the second standard sample.

[0055] The correction curve is established according to the actual spectral line intensity of the first standard sample and the characteristic spectral line theoretical intensity of the sample to be measured.

[0056] The correction curve is established with the actual spectral line intensity of the first standard sample as the abscissa and the characteristic spectral line theoretical intensity of the sample to be measured as the ordinate.

[0057] For example, two standard samples of the same material with similar components and a group of initial samples of the same material to be measured are obtained respectively.

[0058] The initial samples are preliminarily pretreated, including cutting, grinding and polishing, so as to become cylindrical samples with a radius of 3 cm and a height of 40 cm.

[0059] Under the same experimental environment, the cylindrical samples are detected by a laser-induced breakdown spectroscopy system to obtain respective LIBS spectral data, wherein a plurality of LIBS data are collected at different positions of each sample.

[0060] A plurality of LIBS data collected at different positions of each sample are set as a group, each group containing a plurality of LIBS data, and the LIBS data in each group are averaged, that is, an average spectral data is obtained at each position.

[0061] Under the same experimental environment and experimental conditions, a pure sample of the element to be measured is detected by a laser-induced breakdown spectroscopy system to obtain corresponding accurate element spectral lines, and spectral line selection is performed.

[0062] Under the assumption conditions that local thermodynamic equilibrium and plasma optical thinness are met, according to the Boltzmann equation, the integral intensity of the spectrum can be obtained as:

[0063] (1)

[0064] wherein, is the intensity of the emission line at the wavelength λ, F is a constant related to the experimental environment and system, C S is the particle content (number fraction), A ki is the spontaneous emission transition probability from the energy level k to i , is the degeneracy of the upper energy level, U S (T) is the partition function, is the energy of the upper energy level, is the Boltzmann constant, T is the plasma temperature.

[0065] Two emission lines from the same element from the same plasma λ 1 and λ 2, their spectral line intensity ratio can be described as:

[0066] (2)

[0067] where, A ki , , are the same parameters which can be found from the database of National Institute of Standards and Technology (NIST). Once the wavelengths of λ 1 and λ 2 are determined, the values of A ki , , can be determined.

[0068] Under certain experimental conditions, it is assumed that the plasma temperature T of these samples to be measured is a constant, so the right side of equation (2) is equivalent to a constant. For samples of the same material, under given plasma conditions, and are proportional.

[0069] Two emission lines from different samples of the same element and , their intensity ratio can be described as:

[0070] (3)

[0071] where, a and b represent two different samples, is the concentration of the substance in sample a, is the concentration of the substance in sample b.

[0072] When λ1=λ2=λ x , equation (3) can be rewritten as:

[0073] (4)

[0074] Further, for samples of the same material, select multiple spectral lines of different wavelengths of a certain element from two standard samples a , b This spectral line selection process cannot select resonance lines that are prone to self-absorption; then the actual spectral intensity of each spectral line in the standard sample a is: , , , , The actual spectral intensities of each spectral line in standard sample b are selected as follows: , , , , The actual spectral intensities of each spectral line in the sample c to be tested are selected as follows: , , , , .

[0075] Selecting standard samples b Select the first calibration standard. a As the second calibration standard, b The plasma temperature at this moment T As a benchmark, then the standard sample a The theoretical spectral intensities of the selected spectral lines at different wavelengths can be expressed as:

[0076] (5)

[0077] in, x The possible values ​​are 1, 2, 3, ...

[0078] Then select a standard sample a Wavelength is λ x actual spectrum Compared with theoretical spectra The difference between them can be expressed as:

[0079] (6)

[0080] Therefore, the intensity correction factors for multiple spectral lines at each wavelength calculated based on the second correction standard a can be expressed as:

[0081] (7)

[0082] in, x The possible values ​​are 1, 2, 3, ...

[0083] Therefore, the theoretical spectral intensities of each spectral line in the selected sample c can be expressed as:

[0084] (8)

[0085] With standard sample b The actual spectral line intensity selected in the figure is used as the abscissa, and the sample under test is used as the ordinate. c Using the theoretical spectral line intensity as the ordinate, a calibration curve is constructed; then the slope is... K Then formula (4) can be rewritten as:

[0086] (9)

[0087] Then the content of the element in the sample to be tested:

[0088] (10)

[0089] In one possible embodiment, six medium-low alloy steel standard samples are used as the implementation object, and two elements Mn and Ni are selected as the detection target, and the specific steps are as follows:

[0090] 1. For the two elements, two standard samples of the same material with similar compositions and four initial samples to be tested are obtained, and the six samples are recorded as S1, S2, S3, S4, S5 and S6;

[0091] 2. The initial samples are preliminarily pretreated, including cutting, grinding and polishing, so as to become cylindrical samples with a radius of 3 cm and a height of 40 cm;

[0092] 3. Under the same experimental environment, the LIBS spectrum data of each sample is obtained by using a laser-induced breakdown spectroscopy system to detect the cylindrical samples, and multiple LIBS data are collected at different positions of each sample;

[0093] 4. Multiple LIBS data collected at different positions of each sample are set as a group, each group contains multiple LIBS data, and the LIBS data in each group is averaged, that is, an average spectrum data is obtained by averaging each position;

[0094] 6. Record the first calibration standard sample of Mn as S4 and the second calibration standard sample as S5;

[0095] 7. Select different wavelength spectral lines of Mn element, which are 403.08, 403.31, 403.45, 475.40 and 478.34 nm respectively; and select different wavelength spectral lines of Ni element, which are 339.30, 346.17, 349.30 and 352.45 nm respectively;

[0096] 8. The theoretical spectral intensity of different wavelengths is calculated according to formula (5); and the spectral line intensity correction factor of each wavelength is calculated according to formula (6) and (7);

[0097] 9. The theoretical spectral intensity of each spectral line in the sample to be tested is calculated according to formula (8);

[0098] 10. The actual spectral line intensity selected by the first calibration standard sample is taken as the abscissa, and the theoretical spectral line intensity of the sample to be tested is taken as the ordinate, and a calibration curve is established;

[0099] 11. Calculate the element content of the sample to be measured according to formula (10).

[0100] The results are shown in Tables 1, 2, 3, 4, 5. Figure 2 , 3 , 4, 5.

[0101] While the preferred embodiments of the application have been described, modifications and alterations thereto will occur to those skilled in the art upon reading the preceding description. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims and their equivalents.

[0102] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims and their equivalents, the application can be practiced otherwise than as specifically described.

Claims

1. A method for improving the accuracy of LIBS quantification with dual-standard multi-spectral line correction, characterized in that, include: Acquire LIBS spectral data of the sample to be tested and two standard samples; Multiple characteristic spectral lines of the elements to be measured in the sample to be tested and the two standard samples are obtained from the LIBS spectral data. Calculate the spectral intensity correction factor for the second standard sample based on the characteristic spectral line data; The theoretical spectral intensity of the second standard sample is calculated based on the spectral intensity of the first standard sample. The spectral intensity correction factor of the multiple characteristic spectral lines of the second standard sample is calculated based on the difference between the theoretical spectral line intensity corresponding to the second standard sample and the actual intensity of the multiple characteristic spectral lines of the second standard sample. The theoretical intensity of the characteristic spectral lines of the sample to be tested is calculated based on the spectral line intensity correction factor of the second standard sample. A calibration curve is established based on the actual spectral line intensity of the first standard sample and the theoretical intensity of the characteristic spectral lines of the sample to be tested. The content of the analyte element in the sample to be tested is calculated based on the calibration curve. Selecting standard samples b The first standard sample is selected as the standard sample. a As the second standard sample, b The plasma temperature at this moment T As a benchmark, then the standard sample a The theoretical spectral intensities of the selected spectral lines at different wavelengths can be expressed as: Among them, It is the concentration of the substance in sample a. This refers to the concentration of the substance in sample b. x The possible values ​​are 1, 2, 3, ...; Then select a standard sample a Wavelength is λ x actual spectrum Compared with theoretical spectra The difference between them can be expressed as: Therefore, the intensity correction factors for multiple spectral lines at various wavelengths calculated based on the second standard sample a can be expressed as: in, x The possible values ​​are 1, 2, 3, ...; Therefore, the theoretical spectral intensities of each spectral line in the selected sample c can be expressed as: With standard sample b The actual spectral line intensity selected in the figure is used as the abscissa, and the sample under test is used as the ordinate. c Using the theoretical spectral line intensity as the ordinate, a calibration curve is constructed; then the slope is... K Then the formula It can be rewritten as: The content of a certain element in the sample to be tested: 。 2. The method for improving the quantitative accuracy of LIBS with dual-standard multi-spectral line correction according to claim 1, characterized in that, The acquisition of LIBS spectral data for the sample to be tested and two standard samples includes: Set up two standard samples of the same material with similar composition and a set of initial samples of the same material to be tested; The initial sample to be tested is pretreated by cutting, grinding, and polishing to obtain a cylindrical sample to be tested; Multiple LIBS spectral data were obtained by detecting different positions of each of the standard samples and the test samples using LIBS.

3. The method for improving the quantitative accuracy of LIBS with dual-standard multi-spectral line correction according to claim 1, characterized in that, The acquisition of LIBS spectral data for the sample to be tested and two standard samples includes: The average spectral data of each standard sample and the sample to be tested are obtained by averaging the multiple LIBS spectral numbers of each standard sample and the sample to be tested.

4. The method for improving the quantitative accuracy of LIBS with dual-standard multi-spectral line correction according to claim 1, characterized in that, The acquisition of multiple characteristic spectral lines of the analyte elements from the LIBS spectral data of the sample to be tested and the two standard samples includes: The elemental spectral lines corresponding to the element to be tested were obtained by performing LIBS analysis on a pure sample of the element to be tested under the same laboratory environment and experimental conditions as when the LIBS spectral data was obtained. Based on the elemental spectral lines, multiple characteristic spectral line data of the element to be tested in the LIBS spectral data of the sample to be tested and the two standard samples are obtained.

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

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