Laser-induced breakdown spectroscopy analysis system and method based on a suspended electrode and filter paper

Abstract

The present application relates to a kind of spectral analysis system and method, specifically, a kind of laser-induced breakdown spectroscopy analysis system and method based on suspended electrode and filter paper.The system includes filter paper, adjustable sample stage, high-voltage discharge device, suspended electrode, laser ablation device and spectral signal acquisition and analysis device.The present application uses suspended electrode to change the distribution characteristics of high-voltage electric field, increase local electric field line density and electric field intensity, improve the collision frequency of charged particles in plasma, so as to further enhance the detection sensitivity of LIBS to trace elements, and reduce its detection limit.High-voltage discharge device is used to excite laser plasma again, to improve the detection and analysis ability of target elements.Filter paper enrichment method is used for pretreatment of the sample to be measured, which can effectively reduce the interference of liquid matrix on plasma spectral signal, and improve the sensitivity and stability of detection signal.

Description

Technical Field

[0001] This invention relates to a spectral analysis system and method, specifically to a laser-induced breakdown spectral analysis system and method based on a suspended electrode and filter paper. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS), an elemental analysis technique based on atomic emission spectroscopy, enables qualitative and quantitative detection of elements in samples. This technique boasts advantages such as simultaneous detection of multiple elements, minimal damage, remote operation, and rapid in-situ detection, and has been widely applied in fields such as space exploration, artifact authentication, environmental protection, biological detection, and industrial production. However, for the detection of trace elements in liquid samples, existing LIBS techniques still suffer from low sensitivity and high detection limits, limiting their competitiveness and hindering their further development and application. Therefore, this scientific problem has attracted significant attention from researchers.

[0003] When a laser acts on a liquid surface, the liquid is prone to sputtering and bubble formation, hindering the plasma generation and maintenance process (plasma quenching is likely), thus increasing the sample's breakdown threshold and reducing the spectral intensity and signal-to-noise ratio of the target element. Simultaneously, the liquid plasma formation process generates significant fluctuations, leading to reduced repeatability and detection stability of the spectral signal. Therefore, direct measurement of liquid samples severely impairs the qualitative and quantitative analytical performance of LIBS. Existing improvement strategies mainly involve enriching liquid samples before detection, with typical techniques including electrochemical deposition, freezing, or graphite adsorption. Among these, filter paper enrichment is widely used due to its simple operation and short pretreatment time.

[0004] The signal enhancement effect obtained by filter paper enrichment alone is limited, and it usually needs to be combined with discharge-assisted methods to improve the detection sensitivity of LIBS for trace elements in liquids, such as the "Filter Paper Enrichment Combined with High-Voltage Discharge Laser-Induced Breakdown Spectroscopy Analysis Method and System" disclosed in Chinese Patent CN117825357A. However, compared with mass spectrometry, the above methods still have significant gaps in detection sensitivity and detection limit, limiting their application in pharmaceutical, biological, and industrial production fields. Although increasing the discharge voltage can enhance spectral intensity and improve detection sensitivity, excessively high electrical energy may cause electrode melting and corrosion, generating interference signals, thereby reducing the sensitivity and stability of the spectral signal. Therefore, the existing "filter paper enrichment combined with discharge-assisted" LIBS strategy still has certain limitations in improving the detection sensitivity of trace elements in liquids, especially for the detection of trace elements at the ppb level, which is difficult to meet the high sensitivity requirements. Therefore, proposing a LIBS technique that can achieve high sensitivity and real-time speed is the key to solving the quantitative analysis of trace elements in liquid samples. Summary of the Invention

[0005] The purpose of this invention is to address the limitations of existing LIBS strategies combining filter paper enrichment with discharge assistance in improving the detection sensitivity of trace elements in liquids, particularly in meeting the high sensitivity requirements for detecting trace elements at the ppb level. Simultaneously, this invention aims to explore a technical solution that can achieve high detection sensitivity and low detection limits under low energy consumption conditions. To this end, a laser-induced breakdown spectroscopy analysis system and method based on a suspended electrode and filter paper are provided.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper, characterized by: It includes filter paper, an adjustable sample stage, a high-voltage discharge device, a suspended electrode, a laser ablation device, and a spectral signal acquisition and analysis device; The filter paper is placed on the surface of the adjustable sample stage to enrich the liquid sample to be tested; the adjustable sample stage is used to adjust the position of the filter paper. The discharge end of the high-voltage discharge device is positioned above the filter paper to output a high-voltage electric field, thereby providing energy to enhance the emission spectral intensity of the plasma. The suspended electrode is positioned above or below the discharge end of the high-voltage discharge device; at the same time, the suspended electrode is placed on the surface of the adjustable translation stage through an insulating support frame; the suspended electrode is used to change the high-voltage electric field distribution characteristics at the discharge end of the high-voltage discharge device, so as to increase the local electric field line density and electric field strength, increase the collision frequency of charged particles in the plasma, and thus further enhance the emission spectrum intensity of the plasma. The working end of the laser ablation device is set above the discharge end of the suspended electrode or the high-voltage discharge device. It is used to emit laser light to the filter paper surface that enriches the liquid sample to be tested to form a plasma spectral signal. At the same time, the formed plasma spectral signal is output to the acquisition end of the spectral signal acquisition and analysis device. The signal terminal of the laser ablation device is electrically connected to the spectral signal acquisition and analysis device to achieve time synchronization. The spectral signal acquisition and analysis device is used to acquire plasma spectral signals and to identify, analyze, and measure the intensity of the acquired plasma spectral signals, thereby realizing the qualitative and quantitative analysis of target elements in the liquid sample to be tested.

[0007] Furthermore, the suspended electrode is a ring electrode made of metal wire with a diameter of 0.4mm-0.6mm and a diameter of 10mm-14mm. The distance between the suspended electrode and the discharge end of the high-voltage discharge device is 1mm–3mm.

[0008] Furthermore, the high-voltage discharge device operates at a voltage range of 800V–8000V and includes a high-voltage DC power supply, an inductor, a high-voltage diode, a capacitor, a discharge cathode, and a discharge anode. The positive terminal of the high-voltage DC power supply is connected in sequence to the inductor and the high-voltage diode, and the cathode of the high-voltage diode is connected to one end of the capacitor and one end of the discharge anode, respectively. The negative terminal of the high-voltage DC power supply is connected to the other end of the capacitor and one end of the discharge cathode, and is grounded. The other ends of the discharge anode and discharge cathode are arranged opposite each other, with a gap of 3mm–5mm between them; The discharge anode and discharge cathode, serving as the discharge terminals of the high-voltage discharge device, are arranged parallel above the filter paper, with a distance of 2mm–4mm between them.

[0009] Furthermore, the inductance value is 5mH–50mH, and the capacitance value is 5nF–100nF.

[0010] Furthermore, the laser ablation device includes a laser, a reflector, a dichroic mirror, and a first converging lens; The laser is the signal terminal of the laser ablation device and is electrically connected to the spectral acquisition and analysis device. The reflector is placed at the output end of the laser, and the dichroic mirror is placed at the reflecting end of the reflector; The first converging lens is set at the transmission end of the dichroic mirror and serves as the working end of the laser ablation device. It is used to emit laser light to the surface of the sample to be tested to form a plasma spectral signal. At the same time, the formed plasma spectral signal is output to the acquisition end of the spectral signal acquisition and analysis device through the dichroic mirror.

[0011] Furthermore, the laser energy emitted by the laser is 5mJ–200mJ; The focal point of the first converging lens is located 2mm–5mm vertically below the liquid sample to be tested.

[0012] Furthermore, the spectral signal acquisition and analysis device includes a second converging lens, an optical fiber probe, a spectral analyzer, and a spectral data analysis platform; The second converging lens, serving as the acquisition end of the spectral signal acquisition and analysis device, is located at the reflection end of the dichroic mirror. The fiber optic probe is positioned at the output end of the second converging lens to collect plasma spectral signals and obtain plasma characteristic spectra. The output end of the fiber optic probe is electrically connected to the input end of the spectrometer. The spectrometer is used to receive the plasma characteristic spectrum output by the fiber optic probe and obtain plasma spectral data through analysis. The output of the spectrometer and the laser are electrically connected to the spectral data analysis platform. The spectral data analysis platform is used to store, identify, and perform qualitative and quantitative analysis of plasma spectral data based on existing databases, thereby enabling qualitative and quantitative analysis of target elements in the sample to be tested.

[0013] Meanwhile, this invention also provides a laser-induced breakdown spectroscopy analysis method based on a suspended electrode and filter paper. The method, based on the aforementioned laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper, is characterized by including the following steps: Step 1: Evenly drop the liquid sample to be tested onto the surface of the filter paper to enrich the liquid sample to be tested. Then, place the filter paper with the enriched liquid sample to be tested horizontally on the adjustable sample stage. Step 2: A laser is output to the filter paper surface enriched with the sample to be tested by the laser ablation device to form a plasma spectral signal; at this time, a high voltage electric field is generated at the discharge end of the high voltage discharge device, and the plasma is heated and excited by the high voltage electric field, so that the charged particles of the plasma increase exponentially, thereby enhancing the emission spectral intensity of the plasma. Step 3: By changing the distribution characteristics of the high-voltage electric field at the discharge end of the high-voltage discharge device through the suspending electrode, the local electric field line density and electric field strength are increased, the collision frequency of charged particles in the plasma is increased, thereby further enhancing the emission spectrum intensity of the plasma. Step 4: Acquire the plasma spectral signal output from the working end of the laser ablation device through the acquisition end of the spectral signal acquisition and analysis device; Step 5: The acquired plasma spectral signals are identified, analyzed, and their intensity measured using a spectral signal acquisition and analysis device, thereby achieving qualitative and quantitative analysis of the target elements in the liquid sample to be tested.

[0014] Furthermore, step 4 also includes: By adjusting the sample stage to change the interaction position between the laser and the filter paper, the spectral signals corresponding to different regions of the liquid sample to be tested are obtained, and the average value is taken as the final spectral signal for identification, analysis and intensity measurement.

[0015] The beneficial effects of this invention are: 1. Using a suspended electrode can change the distribution characteristics of the high-voltage electric field, increase the local electric field line density and electric field strength, and promote the collision frequency of charged particles in the plasma, thereby further enhancing the sensitivity of LIBS for qualitative and quantitative analysis of trace elements. 2. The filter paper enrichment method is used to pretreat the sample, which has the advantages of simple operation and short time, which is consistent with the simple characteristics of LIBS pretreatment. At the same time, this method can effectively reduce the interference of liquid matrix on plasma spectral signal and improve the sensitivity and stability of detection signal.

[0016] 3. Using a high-voltage discharge device to re-excite the laser plasma can greatly enhance the spectral signal intensity of the plasma and improve the ability to detect and analyze target elements.

[0017] 4. The analysis system has the advantages of compact optical path structure, simple construction steps, and low device cost, and has good repeatability and industrialization potential. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention (the adjustable translation stage is not shown in the figure). Figure 2 This is a schematic diagram of the high-voltage discharge device in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the structure of Embodiment 2 of the present invention (the adjustable translation stage is not shown in the figure). Figure 4 This is a schematic diagram of the high-voltage discharge device in Embodiment 2 of the present invention; Figure 5 Comparison of calcium ion spectra in lubricating oil using traditional LIBS (Filter paper & Conventional LIBS, FP&C-LIBS), high-voltage discharge-assisted LIBS (Filter paper & Discharge-assisted LIBS, FP&D-LIBS), and the suspended electrode method combined with high-voltage discharge-assisted LIBS (Filter paper & Discharge-assisted LIBS & Floating electrode, FP&D-LIBS & FE) in Examples 1 and 2 of this invention. Figure 6Comparison of sodium ion spectra of lubricating oil using traditional LIBS technology based on filter paper enrichment (FP&C-LIBS), high-voltage discharge assisted LIBS technology (FP&D-LIBS), and the suspended electrode method combined with high-voltage discharge assisted LIBS technology (FP&D-LIBS&FE) in Examples 1 and 2 of this invention. Figure 7 The diagram shows the discharge structure when the discharge voltage is 2000V. (a) is a structural diagram of the suspension electrode located 2mm above the discharge electrode in Embodiment 1 of the present invention, (b) is a structural diagram of the existing structure without a suspension electrode, and (c) is a structural diagram of the suspension electrode located 2mm below the discharge electrode in Embodiment 2 of the present invention. Figure 8 The diagram shows the two-dimensional spatial electric field intensity distribution of the plasma region when the discharge voltage is 2000V. (a)–(d) are the field intensity diagrams when the suspended electrode is 2 mm above the discharge electrode in Embodiment 1 of the present invention, (e)–(h) are the field intensity diagrams when there is no suspended electrode in the present invention, and (i)–(l) are the field intensity diagrams when the suspended electrode is 2 mm below the discharge electrode in Embodiment 2 of the present invention.

[0019] The attached figures are labeled as follows: 1-Filter paper, 2-Adjustable sample stage; 3-High voltage discharge device, 31-High voltage DC power supply, 32-Inductor, 33-High voltage diode, 34-Capacitor, 35-Discharge cathode, 36-Discharge anode; 4-Floating electrode, 5-Laser, 6-Reflector, 7-Dichroic mirror, 8-First converging lens, 9-Second converging lens, 10-Fiber optic probe, 11-Spectrometer, 12-Spectral data analysis platform. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1:

[0022] This invention provides a laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper, such as... Figure 1 and Figure 2 As shown, the system includes filter paper 1, adjustable sample stage 2, high-voltage discharge device 3, suspended electrode 4, laser ablation device, and spectral signal acquisition and analysis device.

[0023] Filter paper 1 is specifically a medium-speed filter paper, mainly used for enriching the liquid sample to be tested. A microliter of the liquid sample to be tested is dropped onto the surface of filter paper 1. After the liquid sample is fully absorbed and enriched, filter paper 1 is placed on the upper surface of the insulated adjustable sample stage 2. The position of filter paper 1 can be easily adjusted using the adjustable sample stage 2. The adjustable sample stage 2 has three-dimensional adjustment capabilities, used to accurately locate the laser focus and discharge center position to achieve the best excitation effect.

[0024] See Figure 2 Specifically, in this embodiment, the high-voltage discharge device 3 mainly includes a high-voltage DC power supply 31, an inductor 32, a high-voltage diode 33, a capacitor 34, a discharge cathode 35, and a discharge anode 36.

[0025] The high-voltage discharge device 3 has an adjustable operating voltage ranging from 800V to 8000V and is used to output a high-voltage electric field to provide energy-enhancing plasma emission spectral intensity before and after laser breakdown.

[0026] The high-voltage DC power supply 31 can operate when connected to an AC power supply with a voltage of 220V and a frequency of 50Hz. The positive terminal of the high-voltage DC power supply 31 is connected in sequence to an inductor 32 and a high-voltage diode 33. The inductance value of the inductor 32 is 5mH–50mH. The cathode of the high-voltage diode 33 is connected to one end of a capacitor 34 and one end of a discharge anode 36. The capacitance value of the capacitor 34 is 5nF–100nF. The negative terminal of the high-voltage DC power supply 31 is connected to the other end of the capacitor 34 and one end of the discharge cathode 35, and is grounded. The other ends of the discharge anode 36 and the discharge cathode 35 are positioned opposite each other, with a distance of 3mm–5mm between them. The discharge anode 36 and the discharge cathode 35 serve as the discharge terminals of the high-voltage discharge device 3, and are arranged parallel to each other above the filter paper 1, perpendicular to the laser incident direction, with a distance of 2mm–4mm between them and the filter paper 1.

[0027] Optionally, the discharge anode 36 and the discharge cathode 35 are made of copper-tungsten alloy and are rod-shaped.

[0028] In this circuit, a high-voltage DC power supply 31, an inductor 32, a high-voltage diode 33, and a capacitor 34 are connected in series to form a charging circuit, which is used to charge the capacitor 34 and store a large amount of charge. In the discharge circuit, the positive and negative terminals of the capacitor 34 are connected to the anode and cathode of the discharge electrode, respectively.

[0029] The material of the suspended electrode 4 is a highly conductive metal, specifically a ring electrode made of metal wire with a diameter of 0.4mm-0.6mm and a diameter of 10mm-14mm.

[0030] See Figure 1The suspended electrode 4 is positioned above the discharge end of the high-voltage discharge device 3. Simultaneously, the suspended electrode 4 is fixed by an insulated polytetrafluoroethylene (PTFE) support frame, which rests on the surface of an adjustable translation stage (not shown in the figure), allowing for precise adjustment of the position of the suspended electrode 4. The suspended electrode 4 remains insulated, and its potential can be considered zero. The suspended electrode 4 is used to alter the high-voltage electric field distribution characteristics at the discharge end of the high-voltage discharge device 3, thereby increasing the local electric field line density and electric field strength, enhancing the collision frequency of charged particles in the plasma, and further strengthening the emission spectrum intensity of the plasma.

[0031] The laser ablation device includes a laser 5, a reflector 6, a dichroic mirror 7, and a first converging lens 8. The laser 5 is specifically an Nd:YAG solid-state laser with an emitted laser energy of 5mJ–200mJ, and its focal point is located 2mm–5mm vertically below the sample. The reflector 6 is located at the output end of the laser 5, and the dichroic mirror 7 is located at the reflecting end of the reflector 6. The first converging lens 8 is located at the transmitting end of the dichroic mirror 7, and its focal point is located 2mm–5mm vertically below the liquid sample to be tested. It serves as the working end of the laser ablation device, used to emit laser light onto the surface of the sample to form a plasma spectral signal. Simultaneously, the generated plasma spectral signal is output through the dichroic mirror 7 to the acquisition end of the spectral signal acquisition and analysis device.

[0032] The emitted laser beam is coupled sequentially through a reflecting mirror 6, a dichroic mirror 7, and a first converging lens 8 before being incident perpendicularly onto the sample surface, forming a plasma spectral signal. The plasma rapidly expands outward along the normal to the sample surface. Since the plasma is located between the discharge cathode 35 and the discharge anode 36, the free electrons and ions in the plasma act as seed charges, activating the discharge circuit. When high-energy electrical energy is injected, the plasma is re-excited, and the number of charged particles increases exponentially, resulting in an enhanced emission spectral intensity. Simultaneously, the levitation electrode 4, located above the discharge electrode, alters the local high-voltage electric field distribution, increasing the electric field linear density and intensity within the annular region. This enhances the collision frequency of charged particles in the plasma, further strengthening the plasma's emission spectral signal intensity.

[0033] The spectral signal acquisition and analysis device includes a second converging lens 9, an optical fiber probe 10, a spectrometer 11, and a spectral data analysis platform 12. The second converging lens 9, serving as the acquisition end of the spectral signal acquisition and analysis device, is located at the reflecting end of the dichroic mirror 7. The optical fiber probe 10 is located at the emitting end of the second converging lens 9 and is used to acquire plasma spectral signals and obtain plasma characteristic spectra. The output end of the optical fiber probe 10 is electrically connected to the input end of the spectrometer 11. The output end of the spectrometer 11 and the laser 5 are connected to the spectral data analysis platform 12 via data connection lines to achieve time synchronization. The spectrometer 11 receives the plasma characteristic spectra output by the optical fiber probe 10 and obtains plasma spectral data through analysis. The spectral data analysis platform 12 stores, identifies, and performs qualitative and quantitative analysis of the plasma spectral data based on an existing database, realizing qualitative and quantitative analysis of target elements in the sample under test.

[0034] The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper in Embodiment 1 of this invention has the following specific operating steps: Step 1: Use a dropper to evenly drop a microliter of the liquid sample to be tested onto the surface of filter paper 1, let it stand for a few minutes to enrich the liquid sample, and then place the filter paper 1 with the enriched liquid sample horizontally on the adjustable sample stage 2.

[0035] Step 2: The positive terminal of the high-voltage DC power supply 31 is connected sequentially to the positive terminals of inductor 32, high-voltage diode 33, and capacitor 34. The negative terminal of the high-voltage DC power supply 31 is connected to the negative terminal of capacitor 34 and grounded to charge capacitor 34. Simultaneously, the positive terminal of capacitor 34 is connected to discharge anode 36, and the negative terminal of capacitor 34 is connected to discharge cathode 35 to discharge capacitor 34. Discharge cathode 35 and discharge anode 36 are placed parallel and facing each other above filter paper 1 containing the liquid sample. The high-voltage DC power supply 31 can operate when connected to an AC power supply with a voltage of 220V and a frequency of 50Hz. After charging is complete, capacitor 34 will store a large amount of charge, which will be discharged through discharge anode 36 and discharge cathode 35, thereby forming a high-voltage electric field above filter paper 1.

[0036] Step 3: A laser beam emitted by laser 5 passes through mirror 6, dichroic mirror 7, and first converging lens 8, and is then vertically focused onto the surface of filter paper 1 containing the liquid sample, inducing plasma generation in the liquid sample. At this point, a large number of free electrons and ions in the plasma act as seed charges between the high-voltage discharge electrodes, causing the circuit to connect and generate spark discharge. A large amount of charge in capacitor 34 is injected into the plasma, achieving reheating and excitation of the plasma, resulting in an exponential increase in the number of charged particles in the plasma and a significant enhancement in the intensity of the plasma spectral signal. During the experiment, the interaction position between the laser and filter paper 1 is changed by moving the three-dimensional adjustable sample stage 2, and the influence of measurement error on the experimental results is reduced by averaging the emission spectra obtained from different sample regions.

[0037] Step 4: Place the annular levitation electrode 4 above the discharge electrode, ensuring that its geometric center is in the same vertical direction as the laser focus. Under the action of the levitation electrode 4, the high-voltage electric field distribution changes, the electric field linear density increases and the electric field strength is enhanced within the annular region of the levitation electrode 4. This increases the collision frequency between charged particles in the plasma, thereby further enhancing the emission spectrum intensity of the plasma.

[0038] Step 5: The spectral signal generated by the plasma is reflected by the first converging lens 8 and the dichroic mirror 7, and then converged and collected by the second converging lens 9 before entering the fiber optic probe 10. The fiber optic probe 10 is connected to the spectrometer 11, which can detect the optical signal. Subsequently, the collected spectral data is stored, identified, and qualitatively and quantitatively analyzed using the existing database through a spectral analysis platform.

[0039] Example 2:

[0040] See Figure 3 and Figure 4 The difference between this embodiment and Embodiment 1 is that the suspended electrode 4 is positioned below the discharge end of the high-voltage discharge device 3, while the working end of the laser ablation device is positioned above the discharge end of the high-voltage discharge device 3. The other structures of this embodiment are the same as in Embodiment 1.

[0041] The specific operation steps of Embodiment 2 of the present invention are similar to those of Embodiment 1. Only the setting position of the corresponding device needs to be adjusted according to the differences.

[0042] according to Figure 5It can be seen that, compared with high-voltage discharge-assisted LIBS technology alone (blue line), the introduction of levitation electrode 4 significantly enhances the spectral intensities of Ca II at 393.36 nm and 396.84 nm. When using the upper levitation electrode 4 (green line), the two spectral intensities are enhanced by 1.49 times and 1.73 times, respectively; when using the lower levitation electrode 4 (red line), the two spectral intensities are enhanced by 1.72 times and 1.87 times, respectively. The results show that adding levitation electrode 4 in a high-voltage electric field effectively enhances the spectral intensity of laser plasma.

[0043] according to Figure 6 It can be seen that, compared with using only high-voltage discharge-assisted LIBS technology (blue line), the introduction of levitation electrode 4 also significantly enhances the spectral intensities of Na I at 588.99 nm and 589.59 nm. When using the upper levitation electrode 4 (green line), the two spectral intensities are enhanced by 2.63 times and 1.81 times, respectively; when using the lower levitation electrode 4 (red line), the two spectral intensities are enhanced by 3.11 times and 1.88 times, respectively. This result further indicates that, under a high-voltage electric field environment, using levitation electrode 4 will significantly enhance the spectral intensity of laser plasma.

[0044] See Figure 7 When the discharge voltage is 2000V, and the floating electrode 4 is located 2mm above or below the discharge electrode, a simulation experiment is conducted with no floating electrode 4 as a control. The results are as follows: Figure 8 The result image.

[0045] according to Figure 8 As can be seen, compared with high-voltage discharge-assisted LIBS technology alone (Figure eh), the introduction of the levitation electrode 4 can significantly change the high-voltage electric field distribution characteristics at the discharge end, that is, the local electric field lines are more concentrated and the local electric field intensity is significantly improved. Whether the levitation electrode 4 is placed above (Figure ad) or below (Figure il) the discharge electrode, it can generate a higher electric field line density and a stronger electric field intensity near the plasma region.

[0046] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper, characterized in that: It includes filter paper (1), adjustable sample stage (2), high voltage discharge device (3), suspended electrode (4), laser ablation device and spectral signal acquisition and analysis device; The filter paper (1) is placed on the surface of the adjustable sample stage (2) to enrich the liquid sample to be tested; the adjustable sample stage (2) is used to adjust the position of the filter paper (1); The discharge end of the high-voltage discharge device (3) is located above the filter paper (1) and is used to output a high-voltage electric field to provide energy-enhanced plasma emission spectral intensity. The suspended electrode (4) is positioned above or below the discharge end of the high-voltage discharge device (3); at the same time, the suspended electrode (4) is placed on the surface of the adjustable translation stage through an insulating support frame; the suspended electrode (4) is used to change the high-voltage electric field distribution characteristics at the discharge end of the high-voltage discharge device (3) to increase the local electric field line density and electric field strength, increase the collision frequency of charged particles in the plasma, and thus further enhance the emission spectrum intensity of the plasma. The working end of the laser ablation device is set above the discharge end of the suspended electrode (4) or the high-voltage discharge device (3) to emit laser light to the surface of the filter paper (1) enriched with the liquid sample to be tested to form a plasma spectral signal, and at the same time output the formed plasma spectral signal to the acquisition end of the spectral signal acquisition and analysis device. The signal terminal of the laser ablation device is electrically connected to the spectral signal acquisition and analysis device to achieve time synchronization; the spectral signal acquisition and analysis device is used to acquire plasma spectral signals, and to identify, analyze and measure the intensity of the acquired plasma spectral signals, thereby realizing qualitative and quantitative analysis of target elements in the liquid sample to be tested.

2. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 1, characterized in that: The suspended electrode (4) is a ring electrode made of metal wire with a diameter of 0.4mm-0.6mm and a diameter of 10mm-14mm. The distance between the suspended electrode (4) and the discharge end of the high-voltage discharge device (3) is 1mm–3mm.

3. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 1 or 2, characterized in that: The high-voltage discharge device (3) operates in the voltage range of 800V–8000V and includes a high-voltage DC power supply (31), an inductor (32), a high-voltage diode (33), a capacitor (34), a discharge cathode (35), and a discharge anode (36). The positive terminal of the high voltage DC power supply (31) is connected in sequence to the inductor (32) and the high voltage diode (33), and the cathode of the high voltage diode (33) is connected to one end of the capacitor (34) and one end of the discharge anode (36), respectively. The negative terminal of the high-voltage DC power supply (31) is connected to the other end of the capacitor (34) and one end of the discharge cathode (35), respectively, and grounded; The other ends of the discharge anode (36) and discharge cathode (35) are arranged opposite each other, and there is a gap of 3mm-5mm between them; The discharge anode (36) and discharge cathode (35) serve as the discharge ends of the high-voltage discharge device (3), and are arranged in parallel above the filter paper (1), with a distance of 2mm–4mm between them and the filter paper (1).

4. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 3, characterized in that: The inductance of the inductor (32) is 5mH–50mH, and the capacitance of the capacitor (34) is 5nF–100nF.

5. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 1 or 2, characterized in that: The laser ablation device includes a laser (5), a reflector (6), a dichroic mirror (7), and a first converging lens (8); The laser (5) is the signal terminal of the laser ablation device and is electrically connected to the spectral acquisition and analysis device; The reflector (6) is located at the output end of the laser (5), and the dichroic mirror (7) is located at the reflecting end of the reflector (6); The first converging lens (8) is set at the transmission end of the dichroic mirror (7) and serves as the working end of the laser ablation device. It is used to emit laser light to the surface of the sample to be tested to form a plasma spectral signal. At the same time, the formed plasma spectral signal is output to the acquisition end of the spectral signal acquisition and analysis device through the dichroic mirror (7).

6. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 5, characterized in that: The laser energy emitted by the laser (5) is 5mJ–200mJ; The focal point of the first converging lens (8) is located 2mm–5mm below the liquid sample to be tested.

7. The laser-induced breakdown spectroscopy analysis system based on a suspended electrode and filter paper according to claim 5, characterized in that: The spectral signal acquisition and analysis device includes a second converging lens (9), an optical fiber probe (10), a spectral analyzer (11), and a spectral data analysis platform (12); The second converging lens (9) serves as the acquisition end of the spectral signal acquisition and analysis device and is located at the reflection end of the dichroic mirror (7); The fiber optic probe (10) is set at the output end of the second converging lens (9) to collect plasma spectral signals and obtain plasma characteristic spectra; The output end of the fiber optic probe (10) is electrically connected to the input end of the spectrometer (11). The spectrometer (11) is used to receive the plasma characteristic spectrum output by the fiber optic probe (10) and obtain plasma spectral data through analysis. The output of the spectrometer (11) and the laser (5) are electrically connected to the spectrometer data analysis platform (12), respectively. The spectrometer data analysis platform (12) is used to store, identify and perform qualitative and quantitative analysis of plasma spectral data according to the existing database, so as to realize the qualitative and quantitative analysis of target elements in the sample to be tested.

8. A laser-induced breakdown spectroscopy method based on a suspended electrode and filter paper, employing the laser-induced breakdown spectroscopy system based on a suspended electrode and filter paper as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Evenly drop the liquid sample to be tested onto the surface of the filter paper (1) to enrich the liquid sample to be tested. Then place the filter paper (1) containing the liquid sample to be tested horizontally on the adjustable sample stage (2). Step 2: The laser is output to the surface of the filter paper (1) enriched with the sample by the laser ablation device to form a plasma spectral signal; at this time, a high voltage electric field is generated at the discharge end of the high voltage discharge device (3), and the plasma is heated and excited by the high voltage electric field, so that the charged particles of the plasma increase exponentially, thereby enhancing the emission spectral intensity of the plasma. Step 3: By changing the distribution characteristics of the high voltage electric field at the discharge end of the high voltage discharge device (3) through the floating electrode (4), the local electric field line density and electric field strength are increased, the collision frequency of charged particles in the plasma is increased, thereby further enhancing the emission spectrum intensity of the plasma. Step 4: Acquire the plasma spectral signal output from the working end of the laser ablation device through the acquisition end of the spectral signal acquisition and analysis device; Step 5: The acquired plasma spectral signals are identified, analyzed, and their intensity measured using a spectral signal acquisition and analysis device, thereby achieving qualitative and quantitative analysis of the target elements in the liquid sample to be tested.

9. The laser-induced breakdown spectroscopy analysis method based on a suspended electrode and filter paper according to claim 8, characterized in that, Step 4 also includes: By adjusting the sample stage (2) to change the interaction position of the laser and the filter paper (1), the spectral signals corresponding to different liquid sample regions are obtained, and the average value is taken as the final spectral signal for identification, analysis and intensity measurement.

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