A trace element detection system and method

Abstract

The application discloses a trace element detection system and method, and belongs to the technical field of spectral quantitative detection. The system comprises a laser, a sample stage and a spectral signal acquisition system. The laser ablates a sample to generate plasma after passing through a half-wave plate, a Glan prism, a dichroic mirror and a lens group. The acquisition system comprises a wide / narrow band spectral signal collection system and a trigger system: the wide band system comprises an axial and first lateral light path, couples full spectrum signals to a spectrometer, and is used for matrix identification; the narrow band system comprises a second lateral collection lens, a light splitting element and a UV / visible double channel, each channel is sequentially provided with a neutral density filter, an ultra-narrow band filter and a plano-convex lens, and is connected to a photomultiplier tube to an oscilloscope, and high-sensitivity detection of specific element characteristic spectral lines is realized; and the trigger system is used for triggering the spectrometer to acquire. The wide band and narrow band collaborative architecture is adopted, and both material matrix identification and high-precision quantitative detection of trace elements are considered.

Description

Technical Field

[0001] This application relates to the field of quantitative spectral detection technology, specifically to a trace element detection system and method. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is a classic emission spectroscopy technique. LIBS uses a high-energy pulsed laser beam to ablate the sample, generating plasma. The spectral signal generated by the plasma is collected, and the elemental composition and content of the sample are obtained by analyzing the spectral signal. LIBS has multiple advantages, including simplicity, speed, in-situ detection, and simultaneous detection of multiple components.

[0003] Traditional LIBS uses a high-energy pulsed laser beam focused onto the sample by an optical system. Once the sample is placed on the sample stage, different regions of the sample can be detected. Traditional LIBS employs a CT-type grating spectrometer for simultaneous multi-component detection. This CT-type grating spectrometer utilizes a slit in conjunction with a grating for spectral dispersion. To improve spectral resolution and reduce interference from irrelevant elements on trace elements, a narrower slit is chosen. This narrower slit sacrifices spectral intensity for increased resolution. However, trace elements have weaker spectral signals, and reduced spectral intensity limits their detection limit. Furthermore, the spectrometer detector's ability to detect weak light is limited, which also restricts the accuracy of trace element detection.

[0004] To improve the detection of weak light, an enhanced charge-coupled device (ICCD) is often used in conjunction with a spectrometer. While the ICCD amplifies the weak light signal through its own gain, this amplification leads to the simultaneous amplification of continuous background and noise signals from the plasma, making it difficult to separate the weak signal from the noise. Furthermore, the requirement for dedicated cooling facilities for ICCDs limits their widespread application in trace element detection.

[0005] Photomultiplier tubes (PMTs) have excellent signal enhancement capabilities. However, when a single PMT is used as a detector, it cannot function as a single-channel detector because it lacks a beam splitter. This makes it impossible to simultaneously detect multiple trace elements. Summary of the Invention

[0006] Firstly, this application provides a trace element detection system that addresses the shortcomings of traditional LIBS in terms of multi-component quantity detection and accuracy detection.

[0007] The technical solution of this application is as follows:

[0008] A trace element detection system includes a laser for emitting laser light and a sample stage for placing a sample. The laser light sequentially passes through a half-wave plate, a Glan prism, a dichroic mirror, and a lens group before ablating the sample to generate plasma. The spectral signal of the plasma radiation is acquired by a data acquisition system, which includes:

[0009] A broadband spectral signal collection system includes an axial collection system and a first lateral collection system. The axial collection system uses the lens group as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a dichroic mirror and is coupled to an optical fiber by an axial collection lens and a flange, and then transmitted to a spectrometer. The first lateral collection system has a first lateral collection lens and uses the first lateral collection lens as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a plano-convex lens and a flange, and then is coupled to an optical fiber, and then transmitted to a spectrometer.

[0010] A narrowband spectral signal collection system includes a second lateral collection lens, a beam splitter, and ultraviolet light collection channels and visible light collection channels matched with the beam splitter. Each of the ultraviolet light collection channel and the visible light collection channel is equipped with a photomultiplier tube, and the two photomultiplier tubes are connected to an oscilloscope. Both the ultraviolet light collection channel and the visible light collection channel include a neutral density filter, an ultra-narrowband filter, and a plano-convex lens.

[0011] A triggering system having a PIN tube that triggers a spectrometer by receiving laser light transmitted through a dichroic mirror.

[0012] Furthermore, the center wavelength of the ultra-narrow band filter coincides with the center of the characteristic emission spectral line wavelength of the element to be measured, and its bandwidth is equal to the full width at half maximum (FWHM) of the spectral peak of the element to be measured; the ultra-narrow band filter is located at the peak position of the spectral intensity of the element to be measured in the output spectrum of the spectrometer.

[0013] Furthermore, the sample stage is configured as a three-dimensional displacement platform.

[0014] Furthermore, the spectrometer is equipped with a delay signal generator.

[0015] Secondly, this application provides a trace element detection method based on the system of the first aspect, comprising the following steps:

[0016] Step 1: Determine the element to be detected and its characteristic spectral lines;

[0017] Step 2: Select an ultra-narrowband filter whose center wavelength coincides with the characteristic spectral line wavelength of the element to be detected and whose bandwidth is equal to or slightly greater than the full width at half maximum (FWHM) of the characteristic spectral line.

[0018] Step 3: Determine the imaging position of the characteristic spectral line wavelength on the output surface of the beam splitter, and based on this imaging position, configure the ultra-narrow band filter in the ultraviolet light collection channel and the visible light collection channel;

[0019] Step 4: Place the sample on the sample stage, control the sample stage to move in a stepping motion in the vertical direction, operate the laser to emit laser to ablate the sample and generate plasma, collect the spectral signal of plasma radiation through the acquisition system, and record the position of the sample stage corresponding to the maximum intensity of the spectral signal as the origin.

[0020] Step 5: Using the origin as a reference, move the sample stage to ablate the sample at several locations to correct the spectral signal values ​​read by the PMT in the oscilloscope. After correction, acquire the spectral signals of the sample at each location, calculate the Pearson coefficient between the known spectrum and the sample spectrum, determine whether the matrix is ​​the same based on the Pearson coefficient, and output the content of the element to be measured based on the PMT signal.

[0021] Further, in step five, the spectral signal value read by the PMT in the oscilloscope is corrected using the following formula:

[0022] ;

[0023] In the formula, This represents the corrected PMT spectral signal value. This represents the spectral signal value read from the oscilloscope. A dimensionless proportional parameter. Represents the spectral lines of hydrogen. 、 、 These represent three different nitrogen spectral lines. Indicates the spectral lines of oxygen element. These represent the correction coefficients corresponding to the spectral lines.

[0024] Furthermore, in step five, the sample is ablated at at least six locations along the vertical direction with the origin as the reference, and broadband spectra at each location are collected. The broadband spectra are used as independent variables, and the height deviation of the sample ablation location relative to the origin is used as dependent variables. The partial least squares method is used to establish the correction coefficients and dimensionless scaling parameters corresponding to the fitted spectra.

[0025] Furthermore, in step five, when the Pearson coefficient is greater than 95%, the sample is determined to be of the same matrix; when the Pearson coefficient is less than or equal to 95%, the sample is determined to be of a different matrix; when the Pearson coefficient at positions above 50% is less than or equal to 95%, the sample is determined to be of a different substance.

[0026] Furthermore, when the spectrum of the element to be detected includes the ultraviolet band, the broadband spectral signal collection system adopts lateral collection;

[0027] When the spectrum of the element to be detected does not include the ultraviolet band, the broadband spectral signal collection system adopts lateral collection or axial collection.

[0028] Due to the adoption of the above technical solution, the beneficial effects of this application are as follows:

[0029] 1. This application employs a collaborative acquisition architecture combining broadband and narrowband technologies, integrating matrix identification and trace element detection. Specifically, this application acquires full-spectrum information through a broadband spectral signal acquisition system and uses Pearson correlation coefficients for matrix consistency discrimination, effectively avoiding quantitative bias caused by matrix effects. The narrowband spectral signal acquisition system utilizes a spectroscopic element coupled with an ultra-narrowband filter whose center wavelength is precisely matched to characteristic spectral lines and whose bandwidth is equal to or slightly greater than the full width at half maximum (FWHM) of the spectral peak. The filter is precisely positioned at the spatial imaging location corresponding to the characteristic spectral lines. With the aid of PMT, the detection accuracy of trace elements can be significantly improved.

[0030] 2. This application sets the origin using a three-dimensional displacement platform, ensuring stable excitation conditions. Specifically, this application moves the sample stage vertically while simultaneously ablating and acquiring spectral signals. The position of the maximum signal intensity is used as the zero point of the displacement reference, and a calibration model is established to eliminate the influence of uneven sample surface height on laser energy density, thus ensuring the repeatability and accuracy of quantitative measurements.

[0031] 3. This application achieves multi-dimensional signal correction through air background spectral lines. Different altitudes have varying excitation effects on plasma, resulting in different intensities. PMTs are single-channel and cannot directly correct for altitude-related changes using their own signal. The effect of altitude is that not all energy is transferred to the target material; some energy is used for air breakdown or heat transfer within the sample. The degree of elemental participation in the air also reflects changes in distance. This application uses the spectral line intensities corresponding to the three main elements O, H, and N in the air as correction indicators.

[0032] By utilizing the intensity of characteristic spectral lines in hydrogen, nitrogen, and oxygen air collected by a spectrometer, a correction model containing multiple spectral line weights is constructed to compensate the original PMT signal in real time, effectively correcting signal drift caused by minor defocusing or environmental fluctuations, and improving quantitative robustness.

[0033] 4. This application utilizes a PIN diode to receive the laser pulse transmitted by the dichroic mirror as a trigger signal to simultaneously start the spectrometer acquisition, ensuring that the plasma emission signal is accurately captured within the optimal delay window, thereby improving time resolution and signal stability. Attached Figure Description

[0034] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0035] Figure 1 This application provides a schematic diagram of a trace element detection system.

[0036] Figure 2 A flowchart of a trace element detection method provided in this application;

[0037] Figure 3 This is a schematic diagram of a traditional LIBS detection system;

[0038] In the attached diagram:

[0039] 1. Laser; 2. Half-wave plate; 3. Glan prism; 4. Lens group; 5. Sample; 6. Sample stage; 7. Dichroic mirror; 8. PIN diode; 9. Axial collecting lens; 10. Flange; 11. Optical fiber; 12. Spectrometer; 13. Delay signal generator; 14. Computer; 15. First lateral collecting lens; 16. Spectrometer; 17. Neutral density filter; 18. Ultra-narrow band filter; 19. Plano-convex lens; 20. Photomultiplier tube; 21. Oscilloscope; 22. Laser-induced breakdown spectrum; 23. PMT voltage signal diagram; 24. Second lateral collecting lens. Detailed Implementation

[0040] Based on the background technology described, as shown in the appendix Figure 3 As shown, traditional LIBS technology has significant limitations in trace element detection: to achieve multi-element detection, a CT-type grating spectrometer 12 based on a slit-grating spectral structure is typically used. To improve spectral resolution and suppress interference from neighboring element spectral lines, the slit width is often set very narrow. However, while narrowing the slit improves resolution, it significantly reduces the light flux entering the spectrometer 12, leading to a decrease in overall signal intensity. Since trace elements themselves emit weak spectral lines, further loss of light intensity severely restricts detection sensitivity; in addition, the detectors used in conventional spectrometers 12 have limited response to weak light, making it difficult to effectively capture the characteristic signals of low-concentration elements, thus limiting the detection limit and reliability of LIBS in trace analysis. Based on the above, as shown in the appendix... Figure 1 As shown, this application provides a trace element detection system, including a laser 1 for emitting laser light and a sample stage 6 for placing a sample 5. The laser light passes sequentially through a half-wave plate 2, a Glan prism 3, a dichroic mirror 7, and a lens group 4 before ablating the sample 5 to generate plasma. The spectral signal of the plasma radiation is acquired by an acquisition system.

[0041] After laser 1 emits laser light, it passes through half-wave plate 2 and Glan prism 3 and is refracted by dichroic mirror 7. In specific implementations, the dichroic mirror 7 forms a 45° angle with the incident laser. The refracted laser light is then focused on sample 5 on the surface of sample stage 6 after passing through lens group 4, ablating sample 5 and generating plasma. It should be noted that lens group 4 is used to focus the laser light, and lens group 4 is a combination of multiple lenses; the specific solution can be achieved using existing technology. The light emitted by the plasma is collected by a collection system, which includes:

[0042] A broadband spectral signal collection system includes an axial collection system and a first lateral collection system. The axial collection system uses the lens group 4 as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a dichroic mirror 7 and is coupled to an axial collection lens 9 and a flange 10, then enters an optical fiber 11 and is transmitted to a spectrometer 12. The first lateral collection system has a first lateral collection lens 15 and uses the first lateral collection lens 15 as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a plano-convex lens 19 and a flange 10, then enters an optical fiber 11 and is transmitted to the spectrometer 12.

[0043] In this application, lens group 4 serves two purposes: focusing the laser beam upon incident and converting the plasma light into parallel light. This functional conversion does not require altering the structure of lens group 4 and can be achieved using existing technology. The parallel light, focused by plano-convex lens 19, is collected by flange 10 and coupled into spectrometer 12. In the first lateral collection system, the first lateral collection lens 15 converts the plasma light into parallel light, which is then coupled to flange 10 via plano-convex lens 19 and transmitted to spectrometer 12 via optical fiber 11. It should be noted that in the first lateral collection system, plano-convex lens 19 is a converging lens, and is made of fused silica material. Plano-convex lenses made of fused silica can be used for transmitted ultraviolet spectroscopy. In the axial collection system, since plano-convex lens 19 does not collect ultraviolet light, its material is not limited.

[0044] In the broadband spectral signal acquisition system, the axial acquisition system and the first lateral acquisition system are selectively activated according to the element to be detected. Either the axial acquisition system or the first lateral acquisition system can be activated together with the narrowband spectral signal acquisition system. The narrowband spectral signal acquisition system in the acquisition system has a second lateral acquisition lens 24, a beam splitter 16, and an ultraviolet light acquisition channel and a visible light acquisition channel matched with the beam splitter 16. Each of the ultraviolet light acquisition channel and the visible light acquisition channel is equipped with a photomultiplier tube 20, and the two photomultiplier tubes 20 are connected to an oscilloscope 21. Both the ultraviolet light acquisition channel and the visible light acquisition channel include a neutral density filter 17, an ultra-narrowband filter 18, and a plano-convex lens 19.

[0045] The second lateral collecting lens 24 has the same structure and function as the first lateral collecting lens 15. The second lateral collecting system converts the collected light into parallel light. The parallel light undergoes preliminary light dispersion through the beam splitter 16, and then enters the ultraviolet light collecting channel and the visible light collecting channel, respectively. The two collecting channels have the same structure, but the center wavelengths of the ultra-narrow band filter 18 are different, thus collecting different spectral signals. Specifically, the neutral density filter 17 attenuates the intensity of the collected light to prevent excessive light intensity from damaging the detector. The ultra-narrow band filter 18 achieves spectral dispersion, allowing the spectral wavelength of the element to be detected to pass through while blocking other wavelengths. The filtered light is converged to the PMT to achieve signal collection. It should be noted that each channel collects only one element signal. The visible light collecting channel and the ultraviolet light collecting channel operate on the same principle, collecting signals through the PMT, as shown on the oscilloscope 21. The PMT itself has high sensitivity, making it suitable for weak light detection. Its high sensitivity, combined with the high resolution of the ultra-narrow band filter 18, enables high-precision measurement of trace elements. An ultra-narrowband filter 18 and a high-sensitivity PMT, corresponding to the spectra of the elements, are placed at corresponding spatial positions to form a high-precision multi-element detection channel. The ultra-narrowband filter 18 is configured as follows: its center wavelength coincides with the center of the characteristic emission spectral line wavelength of the element to be measured, and its bandwidth is equal to the full width at half maximum (FWHM) of the spectral peak of the element to be measured; the ultra-narrowband filter 18 is located at the peak intensity position of the spectral intensity of the element to be measured in the output spectrum of the spectroscopic element 16. In specific implementations, the bandwidth of the ultra-narrowband filter 18 can also be slightly larger than the FWHM of the spectral peak of the element to be measured. "Slightly larger" means that the bandwidth of the ultra-narrowband filter 18 is 1.0 to 1.5 times the FWHM of the spectral line to be measured.

[0046] Before ablation, sample 5 needs to be positioned to find its origin. Therefore, in a preferred embodiment of this application, the sample stage 6 is configured as a three-dimensional displacement platform, and the spectrometer 12 is equipped with a delay signal generator 13.

[0047] This application also includes a triggering system with a PIN tube 8, which triggers a spectrometer 12 by receiving laser light transmitted through a dichroic mirror 7. The spectrometer 12 is triggered by the PIN tube 8, which receives the laser light transmitted through the dichroic mirror 7 to generate a trigger signal, which is then transmitted to the spectrometer 12 to achieve triggering. The spectrometer 12 then collects broadband spectra.

[0048] In the trace element detection system of this application, the spectrometer 12 and the oscilloscope 21 undertake different signal acquisition tasks: the spectrometer 12 receives broadband spectral signals and acquires full-spectrum data through its internal detector to generate a laser-induced breakdown spectrum 22, enabling matrix identification and extraction of the intensity of H, N, and O element spectral lines in the air; while the oscilloscope 21 acquires electrical signals from two photomultiplier tubes 20, records the time-resolved intensity of characteristic spectral lines of specific elements, and forms a PMT voltage signal graph 23 for high-precision quantitative analysis. Although the spectrometer 12 and the oscilloscope 21 generate raw spectral data and voltage waveforms respectively, both types of images are ultimately visualized and processed in the computer 14. The computer 14 not only controls the synchronous triggering and parameter setting of the spectrometer 12 and the oscilloscope 21, but also receives and stores their data, and completes matrix correction and trace element content calculation.

[0049] Based on the above system, this application provides a method for detecting trace elements, as shown in the attached figure. Figure 2 As shown, before trace element detection, the optical components, except for the ultra-narrow band filter, must be configured and adjusted. The following steps need to be performed before sample ablation:

[0050] Step 1: Determine the element to be detected and its characteristic spectral lines.

[0051] The application of LIBS technology is to identify samples, i.e., to verify whether a hypothesis holds true. For elements, the signal intensity of the same element differs in different matrices; therefore, when the detected signal intensity differs, it can be determined that the matrices are different. By determining the presence or absence of trace elements, it can be determined whether they are the same substance. In laser-induced breakdown spectroscopy, when a sample is ablated by a laser to form a high-temperature plasma, the atoms / ions within are excited, subsequently cooled, and emit light with fixed wavelengths. These wavelengths are uniquely determined by the electronic energy level structure of the element and are therefore called characteristic spectral lines. An element has multiple spectral lines; therefore, in step one, the spectral line with the least interference must be selected as the characteristic spectral line.

[0052] Step 2: Select an ultra-narrowband filter whose center wavelength coincides with the characteristic spectral line wavelength of the element to be detected and whose bandwidth is equal to or slightly greater than the full width at half maximum (FWHM) of the characteristic spectral line.

[0053] Full width at half maximum (FWHM) refers to the wavelength width of a characteristic spectral line when its intensity drops to half its peak value on the spectral intensity distribution curve. It reflects the natural broadening of the spectral line and its actual width after being affected by the plasma environment. The center wavelength of the selected ultra-narrowband filter coincides with the characteristic spectral line wavelength of the analyte to ensure that the characteristic light signal can pass through the filter to the maximum extent; at the same time, its bandwidth is set to be equal to or slightly greater than the FWHM of the characteristic spectral line. This design achieves two key effects: maximizing the transmittance of the target signal and avoiding the truncation of effective light intensity on both sides of the spectral line due to an excessively narrow filter bandwidth; and effectively suppressing adjacent interfering spectral lines to prevent continuous radiation from other elements or background from entering the detector.

[0054] Step 3: Determine the imaging position of the characteristic spectral line wavelength on the output surface of the beam splitter, and based on this imaging position, configure the ultra-narrow band filter in the ultraviolet light collection channel and the visible light collection channel.

[0055] After the beam splitter separates the light, light of different wavelengths falls on different physical locations. By moving the position of the ultra-narrowband filter and observing the PMT system, the location with the strongest signal and no saturation is selected as the placement position of the ultra-narrowband filter.

[0056] Step 4: Place the sample on the sample stage and control the stage to move vertically in steps. Operate the laser to emit laser light to ablate the sample and generate plasma. Collect the spectral signal of the plasma radiation through the acquisition system, and record the position of the sample stage corresponding to the maximum intensity of the spectral signal as the origin. Subsequent position movements are all based on the origin.

[0057] Step 5: Using the origin as a reference, move the sample stage to ablate the sample at several locations to correct the spectral signal values ​​read by the PMT in the oscilloscope. After correction, acquire the spectral signals of the sample at each location, calculate the Pearson coefficient between the known spectrum and the sample spectrum, determine whether the matrix is ​​the same based on the Pearson coefficient, and output the content of the element to be measured based on the PMT.

[0058] Correct the spectral signal value read from the oscilloscope by the following formula:

[0059] ;

[0060] In the formula, This represents the corrected PMT spectral signal value. This represents the spectral signal value read from the oscilloscope. A dimensionless proportional parameter. Represents the spectral lines of hydrogen. 、 、 These represent three different nitrogen spectral lines. Indicates the spectral lines of oxygen element. These represent the correction coefficients corresponding to the spectral lines.

[0061] The sample was ablated at at least six locations along the vertical direction with the origin as the reference point. Broadband spectra were collected at each location. Using the broadband spectrum as the independent variable and the height deviation of the sample ablation location relative to the origin as the dependent variable, partial least squares method was used to establish the correction coefficients and dimensionless scaling parameters corresponding to the fitted spectra. .

[0062] In step five, when the Pearson coefficient is greater than 95%, the sample is determined to be of the same matrix; when the Pearson coefficient is less than or equal to 95%, the sample is determined to be of a different matrix and is discarded; when the Pearson coefficient at more than 50% of the positions is less than or equal to 95%, the sample is determined to be of a different substance.

[0063] When the spectrum of the element to be detected includes the ultraviolet band, the broadband spectral signal collection system adopts lateral collection.

[0064] When the spectrum of the element to be detected does not include the ultraviolet band, the broadband spectral signal collection system adopts lateral collection or axial collection.

[0065] Broadband spectra obtained by spectrometers contain rich plasma information, which can effectively assist in the quantitative analysis of trace elements using PMT signals. Although PMT can effectively capture the weak emission signals of trace elements due to its high sensitivity, its output is susceptible to the effects of laser-induced plasma fluctuations and elemental self-absorption effects, leading to a deterioration in the linear relationship between signal and concentration and reducing quantitative accuracy. Therefore, this application introduces broadband spectroscopy as supplementary information to correct and optimize the response relationship between PMT signals and elemental concentrations. Specifically:

[0066] Considering the large amount of redundant information in broadband spectra that is unrelated to the target concentration, principal component analysis (PCA) was first used to extract the features most correlated with concentration. The spectral information corresponding to the top 50 principal components with high cumulative contribution rates and strongest correlations was selected and used together with the PMT signal as input variables to construct a partial least squares regression model. After determining the optimal number of principal components, a multivariate regression model was performed with the actual content of trace elements as the dependent variable and the selected spectral features and PMT signal as independent variables to establish a robust quantitative analysis model. The model outputs the trace element content.

[0067] Example 1:

[0068] S1. Select 12 bauxite samples with known composition, mix them with binder in a certain proportion, grind, pulverize, and sieve them, and then select the same mass of cake to prepare 12 samples to be tested.

[0069] S2. Select one sample as the experimental sample for parameter optimization. Adjust the energy by changing the angle of the half-wave plate in front of the Glan prism, and collect the corresponding spectra to determine the optimal value. At the known maximum energy, use a time-delay signal generator to change the detection time of the spectrometer and PMT signal, and collect the corresponding spectra to determine the optimal value.

[0070] S3, the ultra-narrowband filter is configured with center wavelengths of 303.9 nm and 417.2 nm and a bandwidth of 1 nm. The center wavelengths correspond to the characteristic spectral lines of germanium and gallium, respectively.

[0071] The collected data is preprocessed using broadband spectral data to remove outliers. The experimental samples from step S2 are selected, and the PCA method is used to establish the correlation between concentration and each spectral component. The 50 bands with the highest correlation are selected for subsequent calculations.

[0072] S4. Combine the corresponding band signals of the spectra of the 12 samples selected in step S3 with the PMT voltage signal as independent variables and the concentration as dependent variable. Use the PLSR method to establish a quantitative model and fix the model so that the samples can be directly quantitatively calculated later.

[0073] S5. In step S2, select the experimental sample. First, determine the optimal position, i.e., the point with the strongest signal, and designate this as the origin. Move the sample upwards and downwards by 5mm in step size of 0.5mm (a total of 21 positions), and record the corresponding spectrum and PMT signal. Extract the spectral peaks of N, H, and O from the spectrum. Specifically, the spectral peaks of N are selected at 742nm, 744nm, and 746nm, and the spectral peaks of O and H are 777nm and 646nm, respectively. The corresponding correction coefficients were fitted using the spectral and PMT signals from all 21 locations. ,in , , , , These are the spectral lines corresponding to elements H, N, and O, respectively.

[0074] S6. After completing the above steps, test the actual bauxite samples. Collect the corresponding spectra and PMT signals for a series of bauxite samples, and calculate the Pearson coefficient between their spectra and the known standard sample spectra (i.e., the experimental sample spectrum selected in step S3). >95% of the samples were quantitatively calculated. This represents the Pearson coefficient. The spectrum of the selected sample is corrected using the correction model in step S5, and the contents of gallium and germanium are calculated according to the model established in step S3.

[0075] To verify the authenticity of the tests, all bauxite samples were analyzed using X-ray fluorescence spectrometry (XRF) before testing to obtain the gallium and germanium content at corresponding locations. This result was then compared with the final test results to verify the authenticity of the analysis. Since XRF is a non-destructive testing method, it does not affect the surface composition and therefore does not interfere with subsequent testing.

[0076] For any parts not mentioned in this application, existing technologies may be used or referenced.

[0077] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A trace element detection system, comprising a laser for emitting laser light and a sample stage for placing a sample, wherein the laser light sequentially passes through a half-wave plate, a Glan prism, a dichroic mirror, and a lens group to ablate the sample and generate plasma, and the spectral signal of the plasma radiation is acquired by an acquisition system, characterized in that, The data acquisition system includes: A broadband spectral signal collection system includes an axial collection system and a first lateral collection system. The axial collection system uses the lens group as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a dichroic mirror and is coupled to an optical fiber by an axial collection lens and a flange, and then transmitted to a spectrometer. The first lateral collection system has a first lateral collection lens and uses the first lateral collection lens as the first lens to collect plasma light and convert it into parallel light. The parallel light passes through a plano-convex lens and a flange, and then is coupled to an optical fiber, and then transmitted to a spectrometer. A narrowband spectral signal collection system includes a second lateral collection lens, a beam splitter, and ultraviolet light collection channels and visible light collection channels matched with the beam splitter. Each of the ultraviolet light collection channel and the visible light collection channel is equipped with a photomultiplier tube, and the two photomultiplier tubes are connected to an oscilloscope. Both the ultraviolet light collection channel and the visible light collection channel include a neutral density filter, an ultra-narrowband filter, and a plano-convex lens. A triggering system having a PIN tube that triggers a spectrometer by receiving laser light transmitted through a dichroic mirror.

2. The trace element detection system according to claim 1, characterized in that, The center wavelength of the ultra-narrow band filter coincides with the center of the characteristic emission spectral line wavelength of the element to be measured, and its bandwidth is equal to the full width at half maximum (FWHM) of the spectral peak of the element to be measured; the ultra-narrow band filter is located at the peak position of the spectral intensity of the element to be measured in the output spectrum of the spectrometer.

3. The trace element detection system according to claim 2, characterized in that, The sample stage is configured as a three-dimensional displacement platform.

4. The trace element detection system according to claim 3, characterized in that, The spectrometer is equipped with a time delay signal generator.

5. A method for detecting trace elements according to the system of claim 4, characterized in that, Includes the following steps: Step 1: Determine the element to be detected and its characteristic spectral lines; Step 2: Select an ultra-narrowband filter whose center wavelength coincides with the characteristic spectral line wavelength of the element to be detected and whose bandwidth is equal to or slightly greater than the full width at half maximum (FWHM) of the characteristic spectral line. Step 3: Determine the imaging position of the characteristic spectral line wavelength on the output surface of the beam splitter, and based on this imaging position, configure the ultra-narrow band filter in the ultraviolet light collection channel and the visible light collection channel; Step 4: Place the sample on the sample stage, control the sample stage to move in a stepping motion in the vertical direction, operate the laser to emit laser to ablate the sample and generate plasma, collect the spectral signal of plasma radiation through the acquisition system, and record the position of the sample stage corresponding to the maximum intensity of the spectral signal as the origin. Step 5: Using the origin as a reference, move the sample stage to ablate the sample at several locations to correct the spectral signal values ​​read by the PMT in the oscilloscope. After correction, acquire the spectral signals of the sample at each location, calculate the Pearson coefficient between the known spectrum and the sample spectrum, determine whether the matrix is ​​the same based on the Pearson coefficient, and output the content of the element to be measured based on the PMT signal.

6. The trace element detection method according to claim 5, characterized in that, In step five, the spectral signal value read by the PMT on the oscilloscope is corrected using the following formula: ； In the formula, This represents the corrected PMT spectral signal value. This represents the spectral signal value read from the oscilloscope. A dimensionless proportional parameter. Represents the spectral lines of hydrogen. 、 、 These represent three different nitrogen spectral lines. Indicates the spectral lines of oxygen element. These represent the correction coefficients corresponding to the spectral lines.

7. The trace element detection method according to claim 6, characterized in that, In step five, the sample is ablated at at least six locations along the vertical direction with the origin as the reference, and broadband spectra are collected at each location. The broadband spectra are used as independent variables, and the height deviation of the sample ablation location relative to the origin is used as dependent variables. The partial least squares method is used to establish the correction coefficients and dimensionless scaling parameters corresponding to the fitted spectra.

8. The trace element detection method according to claim 7, characterized in that, In step five, when the Pearson coefficient is greater than 95%, the sample is determined to be of the same matrix; when the Pearson coefficient is less than or equal to 95%, the sample is determined to be of a different matrix; when the Pearson coefficient at positions above 50% is less than or equal to 95%, the sample is determined to be of a different substance.

9. The trace element detection method according to claim 7, characterized in that, When the spectrum of the element to be detected includes the ultraviolet band, the broadband spectral signal collection system adopts lateral collection. When the spectrum of the element to be detected does not include the ultraviolet band, the broadband spectral signal collection system adopts lateral collection or axial collection.

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