Ion mobility spectrometer and multiplexing signal processing method thereof

Abstract

The invention relates to an ion mobility spectrometer, which is characterized in that two same dielectric electrodes form an ion source, the inner wall of a quartz capillary dielectric tube of each dielectric electrode is plated with a metal conductive layer, one port of each dielectric tube is sealed, a metal inner electrode of each dielectric electrode is arranged in the corresponding dielectric tube, and a metal outer electrode of each dielectric electrode is arranged in the corresponding dielectric tube. The metal inner electrode is led out from the other port of the dielectric tube through a metal wire, the port is sealed, and the metal wires of the two dielectric electrodes are connected with the positive electrode and the negative electrode of a high-voltage power supply to form a discharge loop. No discharge gap exists between the metal inner electrode and the quartz capillary glass medium tube, exposure and corrosion of the metal inner electrode are avoided, the service life of the ion source is prolonged, discharge is uniform and stable, the ionization effect is good, and the ion yield is high. In addition, ozone in a closed-loop gas path is decomposed at normal temperature, chemical interference is reduced, and a spectrogram is clean. The method is suitable for the scenes of environment VOCs monitoring, food pesticide residue screening, public safety explosive and drug field detection, medical expiration marker analysis and the like.

Description

Technical Field

[0001] This invention belongs to the field of analytical instrument technology, specifically relating to an ion mobility spectrometer for detecting trace substances and its multiplexing signal processing method. Background Technology

[0002] In the field of trace substance detection, ion mobility spectrometry (IMS) has become a core device in environmental monitoring (e.g., VOCs detection), food safety (e.g., pesticide residue screening), public safety (e.g., on-site detection of explosives / drugs), and medical diagnostics (e.g., breath biomarker analysis) due to its advantages such as atmospheric pressure operation, fast detection speed (typically <10s response time), portability (size can be reduced to a portable terminal), low detection limit (from ng / L to pg / L), and lower cost than mass spectrometry (MS). Compared to separation and detection technologies such as gas chromatography (GC) and high-performance liquid chromatography (HPLC), IMS eliminates the need for complex sample pretreatment and chromatographic separation processes, enabling real-time on-site detection. It is irreplaceable in emergency response and field operations, making it an indispensable key piece of equipment in the current trace detection technology system.

[0003] IMS detection is based on the difference in ion mobility. Under atmospheric pressure, sample molecules are ionized by an ion source to form charged ions, which then enter a migration region with a uniform electric field. Under the influence of electric field force and gas resistance, they migrate. Due to the differences in mass, charge number, and molecular structure of different types of ions, their mobility (migration speed per unit electric field strength) is different, and the time to reach the detector (i.e., migration time) is also different. By recording the migration time of ions to the detector and the signal intensity, qualitative (based on migration time) and quantitative (based on signal intensity) analysis of target substances in the sample can be achieved.

[0004] The core structure of an IMS (Inductively Coupled Microscopy) system includes a sample introduction system, an ion source, a migration zone, a detector, and a data processing system. The ion source is the key module determining detection performance—its ionization efficiency directly affects instrument sensitivity, ionization selectivity determines detection specificity, and stability relates to detection repeatability. Specifically, the sample introduction system is responsible for converting gaseous / liquid / solid samples into gaseous molecules that can enter the ion source; the ion source, as the core bottleneck of IMS performance, must achieve efficient ionization of sample molecules; the migration zone uses a uniform electric field and an inert buffer gas (such as nitrogen or clean air) to achieve efficient ion separation; the detector, typically a Faraday disk, converts the ion signal into an electrical signal; and the data processing system analyzes the electrical signal, outputting migration spectra and detection results.

[0005] The performance of the ion source directly determines the applicable scenarios and detection capabilities of IMS. Currently, the mainstream dedicated ion sources for IMS each have their own characteristics. Among radioactive ionization sources, the Ni-63 type emits beta rays (high-energy electrons), which, after ionization of the migrating gas, react with sample molecules to form molecular ions. It has high sensitivity, reaching the pg level for small organic molecules, and good stability. The ionization process is soft ionization, with few fragment ions and a strong molecular ion peak. However, it poses a radiation risk (activity ≤100mCi), requires a radiation safety permit, and has a limited lifespan (half-life 100 years), with sensitivity gradually decreasing over long-term use. The H-3 type emits low-energy beta rays (ionization energy 18.6keV), with sensitivity at the ng level, suitable for polar or thermally unstable substances. The ionization method is soft ionization, with no high-energy fragments, reducing matrix interference. The Am-241 type emits alpha rays (ionization capacity 5.48MeV), with sensitivity reaching the pg level and ionization efficiency superior to Ni-63. However, it has stronger radiation (alpha rays have weak penetrating power but high ionization density), requires strict safety control, and is prone to memory effects caused by sample residue. Vacuum ultraviolet photoionization sources emit photons through vacuum ultraviolet lamps (such as 10.6eV or 11.8eV), causing sample molecules to absorb energy and ionize. The sensitivity is in the ng range, and it is sensitive to aromatic and alkenes. Its soft ionization characteristics result in a molecular ion peak ratio of >90% and fewer fragments. However, it has lower sensitivity to nonpolar or high-ionization-energy substances (such as alkanes), and its negative mode sensitivity is low, usually requiring the addition of chemical reagents to enhance sensitivity. High-energy photoionization (HEPI) sources use low-energy soft X-rays (generally in the energy range of 50-200 eV) as the ionization source. Ionization is achieved through the photoelectric effect between X-ray photons and sample molecules. Its sensitivity reaches the pg level, and its ionization efficiency is better than that of empty ultraviolet photoionization, especially for medium- and high-ionization energy substances (such as alkanes and haloalkanes). The ionization method is also soft ionization. The core disadvantage is that the low-energy soft X-ray source (such as molybdenum target and aluminum target X-ray tube) has a short lifespan (usually <5000h), resulting in high replacement costs. In addition, the X-rays need to be extracted through a thin window (such as a beryllium window), and the window material is easily damaged, leading to frequent maintenance. At the same time, the equipment is slightly larger, and its compatibility with portable IMS needs further optimization.

[0006] Corona discharge ionization (CDI) sources generate corona discharge by applying a high voltage (5-10kV) to the tip electrode, forming plasma to ionize the sample. They offer pg-level sensitivity and fast response (<1s), but the discharge is susceptible to humidity and airflow interference (signal fluctuation ±30% when relative humidity >60%). The tip is also prone to carbon buildup, requiring regular cleaning. Surface ionization (SI) sources rely on the thermal ionization of sample molecules adsorbed onto high-temperature (800-1200℃) metal surfaces (such as tungsten and tantalum). They have lower sensitivity (μg-level) and are only suitable for high-boiling-point, high-electron-affinity substances (such as amines and phosphides). While they can achieve selective ionization to reduce matrix interference, their applicability is extremely narrow. High-temperature metals are prone to oxidation, resulting in a short lifespan (<1000h), and they consume a lot of energy. Electrospray ionization (ESI-IMS) sources atomize sample solutions into charged droplets using high voltage (3-5kV). The solvent evaporates, generating gaseous ions. This method offers high sensitivity (fg level) and is suitable for polar macromolecules (such as antibiotics and proteins). The multi-charged ions generated by soft ionization are well-suited for liquid samples, but require a continuous solvent supply (unsuitable for solid / gaseous samples). The nozzle is prone to clogging, leading to high maintenance costs, and it is not compatible with portable IMS systems. These characteristics indicate that existing dedicated IMS ion sources have significant limitations: radioactive ionization sources are restricted by radiation safety regulations, and their lifespan and sensitivity decrease with use; vacuum ultraviolet photoionization sources have limited applications; HEPI improves the detection of high-ionization-energy substances but is costly and has a short lifespan; CDI has poor stability and is susceptible to environmental interference; SI has a narrow applicability; and ESI-IMS relies on liquid samples and complex auxiliary systems, resulting in poor portability. These shortcomings limit the application of IMS in complex scenarios (such as high-humidity outdoor environments and solvent-free sites), necessitating the development of new ion sources to overcome these bottlenecks.

[0007] Dielectric barrier discharge ionization (DBDI) works based on the principle of dielectric barrier discharge. An insulating dielectric layer (such as quartz or ceramic) is sandwiched between two electrodes. After introducing air or an inert gas and applying high-frequency, high-voltage (1-50 kHz, 1-10 kV), a uniform atmospheric-pressure low-temperature plasma is formed. The active particles (electrons, O₂⁺, OH・) in the plasma react with sample molecules to achieve ionization. Its core advantages are: no radiation risk, eliminating concerns about radioactive isotope safety regulations and soft X-ray protection; strong environmental adaptability, operating under normal pressure and a wide humidity range; compact structure, with a volume that can be reduced to the cm scale, suitable for portable IMS; and the ability to directly ionize gaseous and solid samples without solvents or heating. Based on these advantages, DBDI was first validated for feasibility in mass spectrometry (such as portable MS) and then gradually expanded to IMS.

[0008] Although DBDI has been applied as a mass spectrometry ion source and there are reports of its use as an IMS ion source, its existing technology still suffers from three major drawbacks: First, due to differences in electrode structure, discharge stability is poor, batch-to-batch repeatability is poor, and plasma distribution is easily affected by the dielectric constant of the dielectric layer, electrode spacing, and gas flow rate, resulting in poor detection repeatability and failing to meet the requirements for quantitative detection accuracy. Second, electrode corrosion is severe. Existing DBDIs mostly use exposed stainless steel or copper electrodes, and the active oxygen species generated during discharge will react with the electrode surface, not only reducing ionization efficiency but also requiring frequent electrode replacement, increasing maintenance costs. Third, byproduct interference occurs. During discharge, O2 in the air is excited to produce ozone, which oxidizes sample molecules and corrodes insulating components in the migration region (such as PTFE coating). At the same time, the generated nitrogen oxides compete with sample ions for migration, leading to decreased selectivity and the appearance of unexplained interference peaks. The third drawback is low ion utilization, resulting in a trade-off between resolution and sensitivity.

[0009] The shortcomings of existing DBDI (Dielectric Barrier Discharge) sources, combined with the limitations of traditional IMS (Inductively Coupled Microscopy) ion sources, have become the core bottleneck restricting the upgrading of IMS technology: the safety risks of radioactive sources limit their application in public places such as airports and hospitals; the humidity sensitivity of corona discharge ionization sources (CDI) makes them unsuitable for high-humidity outdoor environments; while HEPI (High-Energy Ionization Source) improves the detection capability of high-ionization-energy substances, its high cost and maintenance threshold further limit its large-scale promotion; and the stability, corrosion, and byproduct problems of DBDI further restrict its large-scale application. Therefore, developing a novel ion source based on dielectric barrier discharge that is "stable in discharge, free from electrode corrosion, and low in byproducts," overcoming the influence of discharge byproducts, and simultaneously improving resolution and sensitivity, has urgent technical value and practical significance. It is the key to breaking through the current bottlenecks of IMS technology and promoting its large-scale application in multiple fields. Summary of the Invention

[0010] The purpose of this invention is to provide a dielectric discharge type ion mobility spectrometer and to provide a method for processing the multiplexed signals of the ion mobility spectrometer.

[0011] To achieve the above objectives, the technical solution of the present invention is an ion mobility spectrometer, comprising an ion source, an ionization reaction chamber, an ion gate, an ion migration chamber, a closed-loop gas path and a circulating gas pump, a Faraday disk detector, a transimpedance amplifier, an information processing and display device, and a high-voltage driving power supply. The ionization reaction chamber, the ion gate, and the ion migration chamber are arranged axially in sequence. The ion gate is located at the junction of the ionization reaction chamber and the ion migration chamber. The sample gas to be tested enters the ionization reaction chamber, and the migration gas is driven into the ion migration chamber by the circulating gas pump through the closed-loop gas path. The waste gas is drawn out of the ionization reaction chamber through the circulating gas pump through the closed-loop gas path. The Faraday disk detector is located inside the ion migration chamber near the port. The Faraday disk detector is electrically connected to the signal processing and display device via the transimpedance amplifier. The invention is characterized in that: the ion... The ion source is located inside the ionization reaction chamber. This ion source is a dielectric barrier discharge ion source, which includes two identical and closely spaced dielectric electrodes arranged vertically and parallel to each other along the radial direction of the ion mobility spectrometer. Each dielectric electrode consists of a metal inner electrode and a quartz capillary dielectric tube. One port of the quartz capillary dielectric tube is sealed, and the metal inner electrode is placed inside the quartz capillary dielectric tube. The metal inner electrode is led out from the other port of the quartz capillary dielectric tube through a metal wire, and then that port is sealed again. The metal inner electrodes of the two dielectric electrodes are respectively connected to the positive and negative terminals of the high-voltage driving power supply through metal wires to form independent discharge circuits. The gas used for the discharge of the dielectric electrodes is nitrogen, inert gas, or dry air, the discharge frequency is 10-50 kHz, and the discharge voltage is 1-5 kV.

[0012] In the above technical solution, the quartz capillary dielectric tube is made of high-purity fused quartz. The inner wall surface of the quartz capillary dielectric tube is first activated by stannous chloride, and then coated with a metal conductive layer by electroplating, chemical plating or magnetron sputtering. The metal conductive layer is made of gold, silver or their alloy, and the thickness of the metal conductive layer is 0.1-1μm. The distance between the metal conductive layer and the sealed end of the metal wire of the quartz capillary dielectric tube is ≥3mm.

[0013] In the above technical solution, the inner diameter of the quartz capillary medium tube is 0.2-1.0 mm, the outer diameter is 0.3-2.5 mm, and the length is 15-20 mm; the quartz capillary medium tube and the ion reaction chamber are sealed and fixed.

[0014] In the above technical solution, the diameter of the inner metal electrode is 0.2-1.0 mm, and the distance between the axes of the two inner metal electrodes is 0.4-2.5 mm.

[0015] In the above technical solution, the diameter of the metal wire in the metal conductor is 0.1-0.9mm; the metal wire passes through the sealed end of the quartz capillary medium tube, and the penetration point is sealed with inorganic adhesive.

[0016] In the above technical solution, in addition to the circulating gas pump, a drying module is also provided in the closed-loop gas path. The circulating gas pump in the closed-loop gas path drives the airflow to pass sequentially through the drying module, the ion migration chamber, the ion gate, and the ionization reaction chamber. The drying module is provided with a packed molecular sieve, which contains a copper-manganese composite ozone decomposition catalyst. The active components of the copper-manganese composite ozone decomposition catalyst are manganese dioxide and copper oxide, with a mass ratio of manganese dioxide to copper oxide of 3:1-5:1. The mass percentage of the copper-manganese composite ozone decomposition catalyst in the packed molecular sieve is 1%-5%.

[0017] In the above technical solution, the circulation flow rate of the closed-loop gas path is 100-500 mL / min.

[0018] In the above technical solution, a plurality of ion migration electrodes are provided in the ion reaction chamber and the ion migration chamber. The ion migration electrodes are parallel plate electrode structures. The ion migration electrodes are made of stainless steel and have gold-plated surfaces. The spacing between the plates of the ion migration electrodes is 3-10 mm, and the length of the plates of the ion migration electrodes is 50-100 mm.

[0019] In the above technical solution, the high-voltage driving power supply also includes an embedded controller. In addition to the switching control circuit, the embedded controller also includes a fully programmable system-on-a-chip (Zynq) core. The switching speed of the polarity of the high-voltage driving power supply by the embedded controller is ≤10ms, the output voltage range of the high-voltage driving power supply is -3kV to +3kV, and the voltage stability is ≤±0.01%. The embedded controller modulates the ion gate and synchronizes with the Faraday disk detector, and performs time-series alignment on the acquired positive and negative ion migration time-domain signals, with a time axis deviation of <1μs.

[0020] In the above technical solution, the multiplexing signal processing method of the ion mobility spectrometer includes the following steps: S1: Ion migration time-domain signals are synchronously acquired using ion gate modulation and a farad disk detector, with a modulation frequency of 0-20 kHz and a sampling accuracy of 16 bits; S2: The time-domain signal f includes polynomial fitting baseline correction, wavelet threshold filtering and signal alignment based on migration time marker peaks, with a time axis deviation of signal alignment <1µs; S3: Perform matched filtering on the preprocessed multi-channel time-domain signals. The matched filtering algorithm adopts the fast Fourier transform algorithm, which enhances the frequency domain signal of the target ion through signal superposition and noise cancellation.

[0021] Advantages and beneficial effects of the present invention: 1. The ion source of this invention employs a dielectric barrier discharge mode, specifically a symmetrical arrangement of two dielectric electrodes. A metal coating layer is added between the inner metal electrode and the inner wall of the quartz glass dielectric tube, thereby modifying the inner surface of the quartz glass dielectric tube. This prevents the gold-plated electrode layer inside the quartz dielectric tube from being exposed. There is no discharge gap between the inner metal electrode and the quartz glass dielectric; discharge occurs only between the two dielectric electrodes within the quartz dielectric tube. This avoids exposure and corrosion of the inner metal electrode, fundamentally solving the problems of uneven discharge and easy electrode corrosion in traditional dielectric barrier discharge methods. The ion source of this invention has an extended lifespan, uniform discharge, high stability, high ion yield, and excellent ionization effect.

[0022] 2. This invention achieves room-temperature ozone decomposition by adding a copper-manganese composite catalyst to the molecular sieve of the drying module of the airflow-driven device. It is simple and efficient, and the ozone concentration after treatment is low, the spectrum is clean, and there is no additional chemical interference. 3. This invention enables the dielectric barrier discharge ion source to generate ions of two polarities by rapidly switching the polarity of the high-voltage power supply, thereby expanding the detection range without replacing components and improving the sensitivity, stability and applicability of the ion mobility spectrometer (IMS).

[0023] 4. This invention uses a multiplexing algorithm to process the time-domain signal, which can improve the ion peak separation by 1 time and reduce the detection limit to the pg level; 5. This invention is applicable to scenarios such as environmental VOCs monitoring, food safety pesticide residue screening, public safety explosives, on-site drug detection, and medical breath biomarker analysis. It aims to solve problems such as unstable discharge, severe electrode corrosion, ozone byproduct interference, insufficient resolution, and unipolar detection limitations of existing corona discharge or dielectric resistance discharge IMS ion sources. It improves the sensitivity, stability, and multi-scenario adaptability of IMS equipment, and promotes the performance upgrade and industrial application of trace detection equipment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the ion mobility spectrometer system of the present invention.

[0025] Figure 2 This is a schematic diagram of the ion mobility spectrometer structure of the present invention.

[0026] Figure 3 This is a schematic diagram of the dielectric barrier discharge ion source structure of the ion mobility spectrometer of the present invention.

[0027] In the attached diagrams above, 1 is the ionization reaction chamber, 2 is the ion gate, 3 is the ion migration chamber, 4 is the ion source, 5 is the high-voltage drive power supply, 6 is the sample gas inlet, 7 is the exhaust gas outlet, 8 is the closed-loop gas path, 9 is the circulating gas pump, 10 is the drying and ozone treatment module, 11 is the migration gas inlet, 12 is the electric field direction, 13 is the migration gas direction, 14 is the Faraday disk detector, 15 is the transimpedance amplifier, and 16 is the signal processing and display device; 101 is the dielectric barrier discharge ion source, 102 is the ion migration electrode in the ionization reaction chamber, 103 is the sample gas inlet, 104 is the exhaust gas outlet, and 105 is... Ion gate, 106 is the ion migration electrode in the ion migration chamber, 107 is the Faraday disk detector, 108 is the migration gas inlet, 109 is the transimpedance amplifier, 110 is the high voltage power supply, 111 is the voltage divider circuit, 112 is the ionization reaction zone, 113 is the migration zone, 114 is the migration gas flow direction, 115 is the electric field direction, i.e., the ion drift direction; 201 is the quartz capillary dielectric tube, 202 is the inner wall coating of the dielectric tube, 203 is the metal inner electrode, 204 is the lower sealed end of the quartz capillary dielectric tube, 205 is the upper sealed end of the quartz capillary dielectric tube, 206 is the metal wire, 207 is the alternating power supply. Detailed Implementation

[0028] Example: The system configuration of the ion mobility spectrometer in this example is shown in the attached figure. Figure 1 As shown.

[0029] The ion mobility spectrometer system of this embodiment includes an ionization reaction chamber 1, an ion gate 2, an ion migration chamber 3, an ion source 4, a high-voltage drive power supply 5, a closed-loop gas path 8 and a circulating gas pump 9, a Faraday disk detector 14, a transimpedance amplifier 15, and an information processing and display device 16. The ionization reaction chamber 1, ion gate 2, and ion migration chamber 3 are arranged axially in sequence. The ion gate 2 is located at the junction of the ionization reaction chamber 1 and the ion migration chamber 3. The ion source 4 is located inside the ionization reaction chamber 1. This ion source is a dielectric barrier discharge ion source. The sample gas to be tested enters the ionization reaction chamber through the sample gas inlet 6. The migration gas is driven by the circulating gas pump through the closed-loop gas path and enters the ion migration chamber 3 from the migration gas inlet 11. The waste gas is drawn out from the waste gas outlet 7 of the ionization reaction chamber 1 through the circulating gas pump through the closed-loop gas path. The Faraday disk detector 14 is located inside the ion migration chamber 3 near the port. The Faraday disk detector 14 is electrically connected to the signal processing and display device 16 through the transimpedance amplifier 15.

[0030] In this embodiment, the high-voltage driving power supply 5 also includes an embedded controller. In addition to the switching control circuit, the embedded controller also includes a fully programmable system-on-a-chip (Zynq) core. The switching speed of the high-voltage driving power supply polarity is ≤10ms, the output voltage range of the high-voltage driving power supply is -3kV to +3kV, and the voltage stability is ≤±0.01%. The embedded controller modulates the ion gate 2 and synchronizes it with the Faraday disk detector 14, and performs time-series alignment on the acquired positive and negative ion migration time-domain signals. The time axis deviation of the signal alignment is <1μs.

[0031] In this embodiment, the closed-loop gas path 8 is equipped with a circulating gas pump 9 and a drying and ozone treatment module 10. The circulating gas pump 9 in the closed-loop gas path 8 sends the waste gas drawn out of the ion reaction chamber into the drying and ozone treatment module 10. After drying and ozone treatment, the gas forms a migration gas that meets the requirements. The migration gas then passes through the ion migration zone, ion gate and ionization reaction zone in sequence to form a closed-loop circulating gas path. The circulation flow rate of the closed-loop gas path is 100-500 mL / min.

[0032] In this embodiment, the drying and ozone treatment module 10 contains a packed molecular sieve, specifically a 13X type molecular sieve, in which a copper-manganese composite ozone decomposition catalyst is mixed. The active components of the copper-manganese composite ozone decomposition catalyst are manganese dioxide and copper oxide, with a mass ratio of manganese dioxide to copper oxide of 3:1-5:1. The mass percentage of the copper-manganese composite ozone decomposition catalyst in the packed molecular sieve is 1%-5%.

[0033] The specific structure of the ion mobility spectrometer in this embodiment is shown in the attached figure. Figure 2 As shown.

[0034] In this embodiment, the dielectric barrier discharge ion source 101 includes two identical and closely spaced dielectric electrodes, which are arranged vertically and parallel to each other along the radial direction of the ion mobility spectrometer. The ionization reaction region 112 is surrounded by the ionization reaction chamber, and the migration region 113 is surrounded by the ion migration chamber. The dielectric barrier discharge ion source 101 is disposed within the ionization reaction chamber. Within the ionization reaction chamber, migration electrodes 102 are arranged radially symmetrically, and within the ion migration chamber, migration electrodes 106 are arranged radially symmetrically. The ion migration electrodes are parallel plate electrodes, made of stainless steel with a gold-plated surface. The distance between the electrode plates is 3-10 mm, and the length of the electrode plates is 50-100 mm. A high-voltage power supply 110 creates a voltage difference between the migration electrodes through a voltage divider circuit 111. The sample gas enters the ionization reaction zone 112 through inlet 103, and the waste gas exits the ionization reaction zone 112 through waste gas outlet 104. The migrating gas, after being treated by the drying and ozone treatment device, enters the ion migration zone 113 through the migrating gas inlet 108. In the figure, the migrating gas flow direction 114 indicates that the migrating gas flows from the migration zone 113 through the ion gate 105 to the ionization reaction zone 112, while the electric field direction 115 indicates the drift direction of the characteristic ions of the sample gas.

[0035] In this embodiment, the dielectric barrier discharge ion source disposed within the ionization reaction chamber includes two identical and closely spaced strip-shaped dielectric electrodes, see Appendix. Figure 3 The two dielectric electrodes are arranged vertically and parallel to each other along the radial direction of the ion mobility spectrometer. Each dielectric electrode consists of a metal inner electrode 203 and a quartz capillary dielectric tube 201. One port 204 of the quartz capillary dielectric tube is sealed, and the metal inner electrode 203 is placed inside the quartz capillary dielectric tube 201. The metal inner electrode 203 is led out from the other port 205 of the quartz capillary dielectric tube through a metal wire 206, and then that port is sealed. The metal inner electrodes 203 of the two dielectric electrodes are respectively connected to the positive and negative terminals of the high-voltage driving power supply 207 through the metal wires 206, forming independent discharge circuits. The gas used for dielectric electrode discharge is nitrogen, inert gas, or dry air, the discharge frequency is 10-50 kHz, and the discharge voltage is 1-5 kV.

[0036] In this embodiment, the quartz capillary dielectric tube 201 is made of high-purity fused quartz. The inner wall surface of the quartz capillary dielectric tube 201 is first activated by stannous chloride, and then a metal conductive layer 202 is deposited by electroplating, chemical plating or magnetron sputtering. The metal conductive layer 202 is made of gold, silver or their alloy, and the thickness of the metal conductive layer 202 is 0.1-1μm. The distance between the metal conductive layer 202 and the upper sealing end 205 of the quartz capillary dielectric tube 201 is ≥3mm.

[0037] In this embodiment, the quartz capillary dielectric tube 201 has an inner diameter of 0.2-1.0 mm, an outer diameter of 0.3-2.5 mm, and a length of 15-20 mm; the quartz capillary dielectric tube 201 is sealed and fixed to the ion reaction chamber.

[0038] In this embodiment, the diameter of the inner metal electrode is 0.2-1.0 mm, and the distance between the axes of the two inner metal electrodes is 0.4-2.5 mm.

[0039] In this embodiment, the diameter of the metal wire in the metal conductor is 0.1-0.9 mm; the metal wire passes through the sealed end of the quartz capillary medium tube, and the penetration point is sealed with inorganic adhesive.

[0040] In this embodiment, the multiplexed signal generated by the ion mobility spectrometer is processed according to the following steps: S1: Ion migration time-domain signals are synchronously acquired through ion gate modulation and a farad disk detector, with a modulation frequency of 0-20 kHz and a sampling accuracy of 16 bits. S2: For the time-domain signal f, polynomial fitting baseline correction, wavelet threshold filtering and signal alignment based on migration time marker peaks are performed, and the time axis deviation of the signal alignment is <1µs; S3: Perform matched filtering on the preprocessed multi-channel time-domain signals. The matched filtering algorithm adopts the fast Fourier transform algorithm, which enhances the frequency domain signal of the target ion through signal superposition and noise cancellation.

[0041] This embodiment demonstrates the use of ion mobility spectrometry to detect trace amounts of industrial toxic and harmful gases (benzene-hydrogen sulfide).

[0042] In this embodiment, the actual detection scenario and sample preparation for the ion mobility spectrometer are as follows: simulating a chemical coating workshop, a mixed gas sample containing benzene (30 pg / L) and hydrogen sulfide (40 pg / L) is prepared, with dry air as the background gas. The sample is introduced into the ion mobility spectrometer at a flow rate of 100 mL / min through a membrane injection device.

[0043] The ion mobility spectrometer parameters are set as follows in this embodiment: In this embodiment, the quartz capillary dielectric tube of the ion source of the ion mobility spectrometer has an inner diameter of 1.0 mm, an outer diameter of 2.5 mm, and a length of 15 mm. The inner wall is activated with stannous chloride and then chemically plated with silver (plating solution temperature 60℃, time 25 min, repeated 4 times). The diameter of the metal inner electrode is 1.0 mm, the metal wire in the lead wire is 0.2 mm silver wire, the discharge gas is air (flow rate 180 mL / min), the frequency is 30 kHz, and the voltage is 6 kV.

[0044] In this embodiment, the gas path system of the ion mobility spectrometer has a circulation flow rate of 400 mL / min, the drying module is filled with 10 g of 13X molecular sieve, and doped with 3% copper manganese catalyst (MnO2:CuO=5:1), and the humidity of the gas path after treatment is ≤1% RH.

[0045] The signal processing and polarity control method of the ion mobility spectrometer in this embodiment is as follows: the signal collected by the Faraday disk detector is amplified by the transimpedance amplifier and then sent to the ADC. The sampling frequency is 100KHz. After Fourier deconvolution, the ion mobility spectrum is obtained. The polarity switching interval is 0.5s (benzene is a positive ion and hydrogen sulfide is a negative ion), the switching speed is 20ms, and the electric field strength is 400V / cm.

[0046] The detection results of this embodiment are as follows: Sensitivity: benzene 0.02 ng / L, hydrogen sulfide 0.04 ng / L, both lower than the industrial exposure limit of GBZ2.1-2019 (formaldehyde 0.5 mg / m³≈430 pg / L); Stability: after continuous detection for 24 hours, the RSD of the three gas signals is ≤2.5%, the RIP peak signal intensity RSD is ≤2%, and there is no electrode corrosion.

[0047] This embodiment verifies that the ion mobility spectrometer provided by the present invention can efficiently detect toxic and harmful gases in industry, is adaptable to complex industrial environments, and provides reliable technical support for safe production monitoring.

Claims

1. An ion mobility spectrometer, comprising an ion source, an ionization reaction chamber, an ion gate, an ion migration chamber, a closed-loop gas path and a circulating gas pump, a Faraday disk detector, a transimpedance amplifier circuit, an information processing and display device, and a high-voltage drive power supply. The ionization reaction chamber, the ion gate, and the ion migration chamber are arranged axially in sequence. The ion gate is located at the junction of the ionization reaction chamber and the ion migration chamber. The sample gas to be tested enters the ionization reaction chamber, and the migration gas is driven into the ion migration chamber by the circulating gas pump through the closed-loop gas path. The waste gas is drawn out of the ionization reaction chamber through the circulating gas pump through the closed-loop gas path. The Faraday disk detector is located inside the ion migration chamber near the port. The Faraday disk detector is electrically connected to the signal processing and display device through the transimpedance amplifier circuit. The feature is that: The ion source is located inside the ionization reaction chamber. This ion source is a dielectric barrier discharge ion source, which includes two identical and closely spaced dielectric electrodes arranged vertically and parallel to each other along the radial direction of the ion mobility spectrometer. Each dielectric electrode consists of a metal inner electrode and a quartz capillary dielectric tube. One port of the quartz capillary dielectric tube is sealed, and the metal inner electrode is placed inside the quartz capillary dielectric tube. The metal inner electrode is led out from the other port of the quartz capillary dielectric tube through a metal wire, and then that port is sealed again. The metal inner electrodes of the two dielectric electrodes are respectively connected to the positive and negative terminals of the high-voltage driving power supply through metal wires to form independent discharge circuits. The gas used for the discharge of the dielectric electrodes is nitrogen, inert gas, or dry air, the discharge frequency is 10-50 kHz, and the discharge voltage is 1-5 kV.

2. The ion mobility spectrometer according to claim 1, characterized in that: The quartz capillary dielectric tube is made of high-purity fused quartz. The inner wall surface of the quartz capillary dielectric tube is first surface activated with stannous chloride, and then coated with a metal conductive layer by electroplating, chemical plating or magnetron sputtering. The metal conductive layer is made of gold, silver or their alloy, and the thickness of the metal conductive layer is 0.1-1μm. The distance between the metal conductive layer and the sealed end of the metal wire of the quartz capillary dielectric tube is ≥3mm.

3. An ion mobility spectrometer according to claim 2, characterized in that: The quartz capillary medium tube has an inner diameter of 0.2-1.0 mm, an outer diameter of 0.3-2.5 mm, and a length of 15-20 mm; the quartz capillary medium tube is sealed and fixed to the ion reaction chamber.

4. An ion mobility spectrometer according to claim 1, characterized in that: The diameter of the inner metal electrode is 0.2-1.0 mm, and the distance between the axes of the two inner metal electrodes is 0.4-2.5 mm.

5. An ion mobility spectrometer according to claim 1, characterized in that, The diameter of the metal wire in the metal conductor is 0.1-0.9 mm; the metal wire passes through the sealed end of the quartz capillary medium tube, and the penetration point is sealed with inorganic adhesive.

6. An ion mobility spectrometer according to claim 1, characterized in that, In the closed-loop gas path, in addition to the circulating gas pump, a drying module is also provided. The circulating gas pump in the closed-loop gas path drives the airflow to pass sequentially through the drying module, the ion migration chamber, the ion gate, and the ionization reaction chamber. The drying module is provided with a packed molecular sieve, which contains a copper-manganese composite ozone decomposition catalyst. The active components of the copper-manganese composite ozone decomposition catalyst are manganese dioxide and copper oxide, with a mass ratio of manganese dioxide to copper oxide of 3:1-5:

1. The mass percentage of the copper-manganese composite ozone decomposition catalyst in the packed molecular sieve is 1%-5%.

7. An ion mobility spectrometer according to claim 6, characterized in that, The circulation flow rate of the closed-loop gas path is 100-500 mL / min.

8. An ion mobility spectrometer according to claim 1, characterized in that, The ion reaction chamber and ion migration chamber are provided with a number of ion migration electrodes. The ion migration electrodes are parallel plate electrode structures. The ion migration electrodes are made of stainless steel and have gold-plated surfaces. The spacing between the plates of the ion migration electrodes is 3-10 mm, and the length of the plates is 50-100 mm.

9. An ion mobility spectrometer according to claim 1, characterized in that, The high-voltage drive power supply also includes an embedded controller. In addition to the switching control circuit, the embedded controller also includes a fully programmable system-on-a-chip (Zynq) core. The switching speed of the high-voltage drive power supply polarity is ≤10ms, the output voltage range of the high-voltage drive power supply is -3kV to +3kV, and the voltage stability is ≤±0.01%. The embedded controller modulates the ion gate and synchronizes it with the Faraday disk detector. It also performs time-series alignment on the acquired positive and negative ion migration time-domain signals, with a time axis deviation of <1μs.

10. An ion mobility spectrometer according to claim 1, characterized in that, The multiplexing signal processing method for the ion mobility spectrometer includes the following steps: S1: Ion migration time-domain signals are synchronously acquired using ion gate modulation and a farad disk detector, with a modulation frequency of 0-20kHz and a sampling accuracy of 16 bits. S2: The time-domain signal f includes polynomial fitting baseline correction, wavelet threshold filtering and signal alignment based on migration time marker peaks, with a time axis deviation of signal alignment <1µs; S3: Perform matched filtering on the preprocessed multi-channel time-domain signals. The matched filtering algorithm adopts the fast Fourier transform algorithm, which enhances the frequency domain signal of the target ion through signal superposition and noise cancellation.

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