Atmospheric volatile organic pollutant tracing unmanned aerial vehicle ion trap mass spectrometry system and application method thereof

Abstract

The application discloses an unmanned aerial vehicle ion trap mass spectrometry system for tracing sources of atmospheric volatile organic pollutants and an application method thereof, and belongs to the technical field of pollutant source tracing and monitoring. The system comprises an unmanned aerial vehicle aerial survey platform and a ground control platform. The unmanned aerial vehicle aerial survey platform comprises an unmanned aerial vehicle and a miniature ion trap mass spectrometer. The miniature ion trap mass spectrometer comprises a sampling unit, a primary cavity, a secondary cavity, a vortex pump and a molecular pump. The sampling unit comprises a conical vortex-preventing groove and a sampling capillary. A detachable heat-conducting screen is arranged in the conical vortex-preventing groove. A heating device is arranged on the outer side of the sampling capillary. The system can combine the high flexibility and high maneuverability of the unmanned aerial vehicle with the strong detection capability of the miniature ion trap mass spectrometer for volatile organic compounds. The system can analyze and trace sources of various volatile pollutants, and has high flexibility, high stability and high detection precision.

Description

Technical Field

[0001] This invention relates to the field of pollutant source tracing and monitoring technology, and in particular to an unmanned aerial vehicle (UAV) ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants and its application method. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Volatile organic compounds (VOCs) are ubiquitous in the atmosphere, diverse in type, and rapidly changing in time and space. They have a significant impact on human health and ambient air quality. On the one hand, many VOCs possess toxicological properties, and direct inhalation can cause various diseases. On the other hand, they are important precursors to ozone and secondary organic aerosol formation, leading to severe environmental pollution events such as ozone pollution and photochemical smog. Therefore, source tracing and monitoring are crucial for addressing VOC pollution.

[0004] For a long time, air pollution source tracing and monitoring technologies have primarily relied on ground-based searches using robots / robots equipped with sensors. However, due to the complexity of the ground environment, the search coverage of robots / robots is limited, and their positioning speed is slow. Drones, due to their high flexibility and maneuverability, can conduct multi-level and multi-dimensional searches, and in recent years have also been developed for emergency source tracing and detection of air pollutants. Currently, much research focuses on using drones in conjunction with odor sensors, wind direction sensors, gas sensors, and other sensing devices, combined with source tracing algorithms, for aerial source tracing; this technology is known as active olfaction technology. However, for the diverse range of volatile organic compounds, the performance and detection range of sensors are very limited, and when used in conjunction with drones for source tracing and detection, comprehensive pollution information from pollution sources cannot be obtained.

[0005] Currently, portable mass spectrometry technology for the detection of volatile organic compounds has become a research hotspot in recent years. Among them, miniature ion trap mass spectrometry has great application potential in the field of volatile organic compound source tracing and monitoring due to its small size, high working pressure and tandem mass spectrometry analysis capability of a single analyzer.

[0006] The team led by Graham R. Cooks at Purdue University has been dedicated to the miniaturization of ion trap mass spectrometry. They proposed a discontinuous atmospheric pressure interface, breaking the limitations of vacuum pumps on mass spectrometry miniaturization, and developed a handheld single-stage vacuum miniature ion trap mass spectrometer that combines atmospheric pressure ionization to detect multiple compounds. However, portable ion trap mass spectrometers with discontinuous atmospheric pressure interfaces suffer from insufficient quantitative stability for volatile organic compounds due to drastic pressure changes. Furthermore, the clamp valve used in discontinuous atmospheric pressure interfaces, which compresses a flexible silicone rubber tube for ion introduction, results in poor long-term robustness. The team led by Xu Wei at Beijing Institute of Technology, using capillary injection, developed a novel two-stage differential vacuum miniature ion trap mass spectrometer with a continuous atmospheric pressure interface, improving instrument stability and robustness. Moreover, this instrument introduces an ion funnel in the first-stage vacuum to focus ions, improving ion transmission efficiency and achieving a toluene detection limit of 10 ppbv. However, for miniature ion trap mass spectrometers used for source tracing and monitoring of volatile organic compounds (VOCs), the ion funnel assembly is complex and suffers from low-mass discrimination, making it difficult to detect compounds with a mass-to-charge ratio below 100 Da. The team led by Li Haiyang at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, constructed a two-stage vacuum differential ion trap mass spectrometry system. They attempted to use a hexapole for ion transport and focusing at 100 Pa in the first-stage differential vacuum system, achieving highly sensitive qualitative and quantitative analysis of VOCs, with a detection limit of 1 ppbv for toluene, while maintaining high stability. However, currently, this instrument is mainly used for short-distance ground-based source tracing and monitoring of pollution sources.

[0007] Currently, there is no existing technology that combines portable ion trap mass spectrometers with drones. Because drones need to start, stop, ascend, descend, accelerate, and decelerate in the air during pollutant tracing, changes in airflow can reduce the detection stability of portable ion trap mass spectrometers, leading to inaccurate results. Therefore, how to provide a drone-based ion trap mass spectrometry system with high detection stability to achieve comprehensive monitoring and tracing of volatile organic compounds in the atmosphere is an urgent problem to be solved. Summary of the Invention

[0008] In view of this, the present invention provides an ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants by drone and its application method. The system can comprehensively monitor and trace the source of volatile organic compounds in the atmosphere, and has high flexibility, high detection accuracy and good detection stability.

[0009] In a first aspect, the present invention provides an ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants using an unmanned aerial vehicle (UAV), comprising an UAV aerial survey platform and a ground control platform;

[0010] The ground control platform is equipped with traceability algorithm software and a communication module;

[0011] The UAV aerial survey platform includes a UAV and a miniature ion trap mass spectrometer; the miniature ion trap mass spectrometer is connected to the UAV.

[0012] The miniature ion trap mass spectrometer includes a sample introduction unit, a primary chamber, a secondary chamber, a vortex pump, and a molecular pump. The primary chamber and the secondary chamber are connected horizontally through a conical electrode. The molecular pump is connected to the secondary chamber through a gas extraction line, and the vortex pump is connected to both the molecular pump and the primary chamber through a gas extraction line.

[0013] The sample introduction unit includes a conical anti-vortex groove and a sample introduction capillary; the central axis of the conical anti-vortex groove is parallel to the horizontal direction, and a detachable heat-conducting screen is installed inside it; the sample introduction capillary includes a horizontal section and a vertical section, one end of the horizontal section of the sample introduction capillary is connected to the bottom of the conical anti-vortex groove, and one end of the vertical section of the sample introduction capillary is connected to the primary cavity; a heating device is installed on the outside of the sample introduction capillary.

[0014] Preferably, the detachable heat-conducting screen is perpendicular to the central axis of the conical anti-vortex groove, the outer ring of the detachable heat-conducting screen abuts against the conical anti-vortex groove, and the diameter of the detachable heat-conducting screen is 1 / 3 to 2 / 3 of the top surface diameter of the conical anti-vortex groove.

[0015] Preferably, the primary cavity contains a radio frequency excitation VUV lamp, a repulsion electrode, an air intake electrode, and a segmental quadrupole radio frequency transmission electrode arranged sequentially in the direction extending toward the secondary cavity. The sample introduction capillary extends radially perpendicular to the radio frequency excitation VUV lamp to the central hole inside the air intake electrode. The diameter of the central hole of the air intake electrode gradually increases in the direction extending toward the secondary cavity.

[0016] Furthermore, the applied voltage of the repulsion electrode in the micro ion trap mass spectrometer is greater than the applied voltage of the inlet electrode, and the voltage difference between the two is less than 10V; a pair of radio frequency AC voltages with a frequency of 2.3MHz, a peak-to-peak value adjustable from 0-500V, and a phase difference of 180° are applied radially to the segment quadrupole radio frequency transmission electrode, and two voltage levels with a gradient decreasing along the direction extending towards the secondary cavity are applied axially, with the voltage difference between the two voltage levels being less than 10V.

[0017] Preferably, a square-aperture electrode, an ion trap front cover electrode, an ion trap mass analyzer, and an ion trap rear cover electrode are sequentially arranged in the secondary cavity along a horizontal direction away from the primary cavity.

[0018] Furthermore, the cone-shaped electrode and the square-shaped electrode are spaced 2-3 mm apart, and the square-shaped electrode and the front cover electrode of the ion trap are spaced 2-3 mm apart. The cone-shaped electrode, the square-shaped electrode, and the front cover electrode of the ion trap together form an electrostatic lens structure.

[0019] Furthermore, an ion detector is also provided in the secondary cavity. The ion detector is an electron multiplier. The central axis of the ion detector is perpendicular to the central axis of the ion trap mass analyzer. The central hole of the ion detector is coaxial with the slit of the ion trap mass analyzer. The ion detector and the ion trap mass analyzer are 5-10 mm apart.

[0020] Furthermore, the ion trap mass analyzer is a hyperboloid linear ion trap. Its Y electrode is subjected to a pair of adjustable radio frequency voltages with a frequency of 1.09 MHz and a peak-to-peak value of 0–5000 V for ion trapping; the X electrode is subjected to a pair of adjustable auxiliary radio frequency voltages with a frequency of 235 kHz and a peak-to-peak value of 0–20 V with a phase difference of 180° for ion ejection; the ion detector is subjected to a voltage of -1400 to -1800 V for receiving ions ejected from the ion trap mass analyzer and realizing amplified detection of ion signals.

[0021] Preferably, the UAV is a multi-rotor transport UAV, and the UAV's fuselage integrates a communication module and a GPS module. The communication module is used to transmit the detection data of the miniature ion trap mass spectrometer to the ground control platform.

[0022] Preferably, the miniature ion trap mass spectrometer is fixed to the underside of the drone fuselage via sheet metal, and the drone is equipped with a camera monitoring device.

[0023] Secondly, the present invention provides a method for applying the above-mentioned ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants using a drone, comprising the following steps:

[0024] When conducting source tracing tasks, the concentration threshold of atmospheric volatile organic pollutants is first input into the source tracing algorithm software on the ground control platform. Then, a drone takes off from a certain location downwind of the polluted area. During the flight, the drone monitors atmospheric volatile organic pollutants in real time using a miniature ion trap mass spectrometer. The detection data from the miniature ion trap mass spectrometer is then transmitted back to the ground control platform via a communication module. The source tracing algorithm software on the ground control platform plans the drone's flight route in real time based on the detection data from the miniature ion trap mass spectrometer and issues flight commands to the drone through communication equipment until the pollution source is found and the source tracing task is completed.

[0025] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0026] (1) This invention is the first to combine a highly flexible and maneuverable UAV with a miniature ion trap mass spectrometer that has a strong detection capability for volatile organic compounds. Compared with the traditional UAV + multiple sensor traceability system, this system only requires one mass spectrometer to complete the analysis of multiple volatile pollutants. While simplifying the traditional traceability system structure, it broadens the traceability application scenarios of volatile organic compounds. It has great application potential in traceability monitoring of volatile organic compound pollution accidents such as factory explosions and gas leaks, and has high detection precision and accuracy.

[0027] (2) In order to avoid the influence of the airflow of the UAV propeller on the mass spectrometer sample introduction, the present invention designed a unique air intake treatment device, adding a conical anti-vortex groove at the mass spectrometer sample inlet, which can change the flow direction of the fluid, so that the vortex gradually dissipates, achieves airflow stability, and thus ensures stable sample collection.

[0028] (3) The sample introduction unit of the present invention is equipped with a detachable heat-conducting screen and a heating device. The heating device can heat the sample introduction capillary, thereby heating and volatilizing the non-volatile components, effectively avoiding the instrument contamination problem that exists during long-term operation of the system. The mesh of the detachable heat-conducting screen can change the direction of the airflow during the sample introduction process, making the sample airflow more stable. At the same time, it can also screen out large-particle floating pollutants. In addition, its good thermal conductivity is conducive to the rapid conduction of heat from the gas heated by the heating device, thereby promoting the volatilization of non-volatile substances on the screen surface, realizing self-cleaning during operation, and avoiding sample introduction blockage. It can be removed from the conical anti-vortex groove for subsequent cleaning. The above settings further enhance the stability of the system. Attached Figure Description

[0029] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0030] Figure 1 This is a schematic diagram of the structure of the ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants by unmanned aerial vehicle (UAV) according to Embodiment 1 of the present invention;

[0031] Figure 2 This invention relates to the quantitative analysis and testing of various volatile organic compounds using a miniature ion trap mass spectrometer in the ion trap mass spectrometry system of the UAV for tracing the source of atmospheric volatile organic pollutants in Embodiment 1 of the present invention; wherein, a is benzene, b is toluene, c is ethyl sulfide, and d is methyl sulfide.

[0032] Figure 3The scan results of benzene and toluene by the miniature ion trap mass spectrometer in the ion trap mass spectrometry system of the UAV for tracing atmospheric volatile organic pollutants in Embodiment 1 of the present invention are shown. Among them, a is the scan spectrum in isolated mode, and b is a comparison of the signal-to-noise ratio of benzene and toluene in isolated mode and full scan mode.

[0033] Figure 4 The resolution test result of the micro ion trap mass spectrometer in the ion trap mass spectrometry system of the UAV for tracing atmospheric volatile organic pollutants in Embodiment 1 of the present invention was obtained by testing 60 ppbv benzene standard gas and then by Gaussian fitting.

[0034] Figure 5 The stability test results were obtained by continuously scanning 100ppbv benzene standard gas 20 times in the ion trap mass spectrometry system of the UAV for tracing atmospheric volatile organic pollutants in Embodiment 1 of the present invention.

[0035] Figure 6 This is a scanning spectrum of a mixed volatile gas with a concentration of 100 ppbv, obtained from the miniature ion trap mass spectrometry system of the UAV ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants in Embodiment 1 of the present invention. In example a, the mixed gas consists of acrolein (characteristic peak 57), acetone (characteristic peak 59), n-butyraldehyde (characteristic peak 71), butenal (characteristic peak 69), pentanal (characteristic peak 85), hexanal (characteristic peak 100), and m-methylbenzaldehyde (characteristic peak 119); in example b, the mixed gas consists of methyl acrylate (characteristic peak 86), ethyl acrylate (characteristic peak 100), dimethyl disulfide (characteristic peak 94), and ethyl acetate (characteristic peak 116).

[0036] In the diagram: the spacing or dimensions between parts have been exaggerated to show their positions; the diagram is for illustrative purposes only.

[0037] The components include: 1. Radio frequency excitation VUV lamp; 2. Repulsion electrode; 3. Inlet electrode; 4. Sample inlet capillary; 5. Segmented quadrupole radio frequency transmission electrode; 6. Conical hole electrode; 7. Square open hole electrode; 8. Ion trap front end cap electrode; 9. Ion trap mass analyzer; 10. Ion trap rear end cap electrode; 11. Ion detector; 12. Molecular pump; 13. Vortex pump; 14. Primary chamber; 15. Secondary chamber; 16. Removable thermally conductive screen; 17. Conical anti-vortex groove; 18. Heating device; 19. Camera monitoring instrument; 20. Unmanned aerial vehicle (UAV); 21. Ground control platform. Detailed Implementation

[0038] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0039] As described in the background section, current technologies for tracing and detecting volatile organic compounds (VOCs) primarily rely on ground-based methods using robots or robotic dogs equipped with sensors. However, the flexibility and maneuverability of these robots / dogs are limited, thus their application scope largely depends on the environment. Aerial tracing mainly uses drones equipped with gas sensors; however, the performance of these gas sensors is often poor, and they can only detect a single substance, limiting the system's application range. Therefore, this invention proposes combining high-performance mass spectrometry with highly flexible and maneuverable drones to provide an ion trap mass spectrometry system for tracing atmospheric VOCs using a drone, along with its application method. The entire system establishes a complete tracing framework, enabling accurate and rapid detection of pollution sources in various complex environments. This system holds great potential for tracing and detecting VOCs.

[0040] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] This embodiment provides an ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone. Please refer to [link to relevant documentation]. Figure 1 This includes unmanned aerial survey platforms and ground control platforms 21.

[0043] The UAV aerial survey platform includes a UAV 20 and a miniature ion trap mass spectrometer. The miniature ion trap mass spectrometer is fixed to the underside of the UAV 20 fuselage via sheet metal. The UAV 20 is equipped with a camera monitoring device 19. The camera monitoring device 19 is used to capture real-time images of the area around the UAV 20, while the miniature ion trap mass spectrometer is used to monitor pollutants around the UAV 20 in real time and determine the material information of atmospheric volatile organic compounds (including material type, concentration, etc.).

[0044] The UAV 20 is preferably a multi-rotor transport UAV 20. The UAV 20 integrates a communication module and a GPS module within its fuselage. The communication module transmits detection data from the miniature ion trap mass spectrometer to the ground control platform 21, while the GPS module is used for precise positioning of the UAV 20. The integration of the communication module and GPS module within the UAV 20's fuselage prevents signal interference and avoids affecting communication and positioning.

[0045] The miniature ion trap mass spectrometer includes a sample introduction unit, a primary chamber 14, a secondary chamber 15, a vortex pump 13, and a molecular pump 12. The primary chamber 14 and the secondary chamber 15 are horizontally connected via a conical electrode 6. The molecular pump 12 is connected to the secondary chamber 15 via a gas extraction line, and the vortex pump 13 is connected to both the molecular pump 12 and the primary chamber 14 via gas extraction lines. The vortex pump 13 is mainly used to maintain the working gas pressure of the ion source in the primary chamber 14 and the working gas pressure of the molecular pump 12. The molecular pump 12 is mainly used to maintain the working gas pressure of the ion trap mass analyzer 9 and the ion detector 11 in the secondary chamber 15.

[0046] The sample introduction unit includes a conical anti-vortex groove 17 and a sample introduction capillary 4. The central axis of the conical anti-vortex groove 17 is parallel to the horizontal direction, which is designed to facilitate sampling. A removable heat-conducting screen 16 is installed inside. The conical anti-vortex groove 17 is preferably a cylindrical conical anti-vortex groove. The conical anti-vortex groove 17 can change the flow direction of the fluid, causing the vortices caused by the airflow from the UAV 20 propeller to gradually dissipate, achieving airflow stability and thus ensuring stable sample collection. The conical anti-vortex groove 17 is made of an alloy material with a surface treated for corrosion resistance and adsorption. Its pore size gradually decreases from the outside to the inside, thereby gradually reducing the intensity of the vortex and stabilizing the airflow.

[0047] The detachable thermally conductive screen 16 is perpendicular to the central axis of the conical anti-vortex groove 17, and the outer ring of the detachable thermally conductive screen 16 abuts against the conical anti-vortex groove 17. The diameter of the detachable thermally conductive screen 16 is 1 / 3 to 2 / 3 of the top surface diameter of the conical anti-vortex groove 17. This is to simultaneously utilize the airflow stabilization function of the conical anti-vortex groove 17 and the detachable thermally conductive screen 16. The detachable thermally conductive screen 16 is woven from metal wire. It can change the airflow direction during sample introduction, making the sample airflow more stable. At the same time, it can also screen out large-diameter floating contaminants. In addition, the detachable thermally conductive screen 16 can also be connected to a heating device (not shown in the figure). Its excellent thermal conductivity can promote the volatilization of non-volatile substances on the screen surface and provide a preheating environment for the air intake. It can be removed from the conical anti-vortex groove 17 for subsequent cleaning.

[0048] Because the cavity is a vacuum environment, gas can be self-absorbed into the miniature ion trap mass spectrometer through the sample introduction capillary 4. The sample introduction capillary 4 includes a horizontal section and a vertical section. One end of the horizontal section of the sample introduction capillary 4 is connected to the bottom of the conical anti-vortex groove 17, and one end of the vertical section of the sample introduction capillary 4 is connected to the primary cavity 14. A heating device 18 is installed on the outside of the sample introduction capillary 4. Its main body is composed of a heating tube, which is directly wrapped around the outside of the mass spectrometer gas inlet capillary. This allows the internal temperature of the capillary to reach 180°C. On the one hand, this prevents volatile pollutants from being adsorbed on the capillary wall, and on the other hand, it allows some less volatile components to be heated and volatilized, thereby entering the cavity and being ionized. Preferably, the inner diameter of the sample introduction capillary 4 is 0.2–0.3 mm.

[0049] Within the primary chamber 14, extending towards the secondary chamber 15, a radio frequency excitation VUV lamp 1, a repulsion electrode 2, an inlet electrode 3, and a segmented quadrupole radio frequency transmission electrode 5 are sequentially arranged. These components are coaxially positioned along the central axis and integrated through supporting fixtures, forming a photochemical ionization source. After sample ionization, ions are focused and transmitted through the segmented quadrupole radio frequency transmission electrode 5, entering the conical electrode 6. The sample introduction capillary 4 extends radially into the central hole of the inlet electrode 3, perpendicular to the radio frequency excitation VUV lamp 1.

[0050] The intake electrode 3 divides the ionization region into a photoionization region and a chemical ionization region. Its central aperture gradually increases along the direction extending towards the secondary cavity 15. Preferably, the central aperture of the intake electrode 3 is expanded from 3 mm to 6 mm. The repulsion electrode 2 is a circular electrode with a central opening of 6 mm. The voltage applied to the repulsion electrode 2 is greater than the voltage applied to the intake electrode 3, and the voltage difference between the two is 0 to 10 V.

[0051] A pair of RF AC voltages with a frequency of 2.3 MHz, a peak-to-peak value adjustable from 0-500 V, and a phase difference of 180° are applied radially to the quadrupole RF transmission electrode 5. After optimization, the ion beam achieves the best focusing effect when the peak-to-peak value is set to 320 V. Gradient voltages V3 and V4 are applied axially, where V3 > V4. The ion transmission efficiency is highest when V3 is set to 23 V and V4 is set to 20 V.

[0052] This invention combines a photochemical ionization source dominated by a radio frequency excitation VUV lamp 1 and a segmented quadrupole radio frequency transmission electrode 5 with an ion trap. By utilizing the high light flux of the radio frequency excitation VUV lamp 1, the radial radio frequency collision focusing of the segmented quadrupole radio frequency transmission electrode 5, and the efficient transmission of axial gradient DC, combined with the ion trap's ability to accumulate and capture ions, highly sensitive detection and analysis of volatile organic compounds can be achieved, with a detection limit of up to 0.5 ppbv. This effectively reduces the difficulty of source tracing tasks and significantly improves the accuracy of system source tracing.

[0053] Inside the secondary chamber 15, along a horizontal direction away from the primary chamber 14, a square-aperture electrode 7, an ion trap front cover electrode 8, an ion trap mass analyzer 9, and an ion trap rear cover electrode 10 are sequentially arranged. The three electrodes—the conical electrode 6, the square-aperture electrode 7, and the ion trap front cover electrode 8—form an electrostatic lens structure. The conical electrode 6 serves as the front electrode, with a central opening of 0.4 mm, and also connects the two vacuum chambers to achieve vacuum differential. The central electrode is the square-aperture electrode 7 with a central opening of 3 mm. The rear electrode is fixed to the ion trap mass analyzer 9 2–3 mm in front by screws; it also serves as the ion trap front cover electrode 8, with a central opening of 2 mm. The three electrodes are spaced 2–3 mm apart to focus sample ions into the ion trap mass analyzer 9.

[0054] The ion trap mass analyzer 9 is a hyperboloid linear ion trap with a hyperboloid radius of 4 mm and a trap length of 40 mm. The left and right hyperboloid electrodes have slits and are mounted on a ceramic fixture. They are integrated with the front and rear end cap electrodes via screws and positioned 2–3 mm behind the front end cap electrode 8 of the ion trap for mass analysis. A pair of 1.09 MHz frequency radio frequency voltages with a peak-to-peak value of 0-5000 V are applied to the Y electrode of the ion trap mass analyzer 9 for ion collection. The ion trap achieves the highest ion collection efficiency when the peak-to-peak value of its operating voltage is set to 300 V. A pair of 235 kHz frequency auxiliary radio frequency voltages with a peak-to-peak value of 0-20 V and a 180° phase difference are applied to the X electrode for ion ejection.

[0055] An ion detector 11 is also installed inside the secondary chamber 15. The central axis of the ion detector 11 is perpendicular to the central axis of the ion trap mass analyzer 9, and it is placed on one side of the ion trap mass analyzer 9. The central hole of the ion detector 11 is coaxial with the slit of the ion trap mass analyzer 9, and it is used to receive ions ejected from the ion trap mass analyzer. The distance between the ion detector 11 and the ion trap mass analyzer 9 is adjusted by screws. After optimization, the best detection effect is obtained when the distance between the two is 10mm. The voltage of the ion detector 11 is related to its lifespan and performance. In order to balance its performance and lifespan, its voltage is finally set to -1700V. At this voltage, it can be used for a long time while maintaining certain performance.

[0056] The ground control platform 21 is equipped with traceability algorithm software and a communication module. The traceability algorithm software plans the aerial survey route of the UAV 20 in real time based on the material information monitored by the miniature ion trap mass spectrometer, and the communication module is used to maintain a connection with the UAV aerial survey platform.

[0057] The miniature ion trap mass spectrometer in this embodiment was tested and analyzed under the optimal conditions selected above. The gas pressure inside the ionization source chamber of the mass spectrometer directly affects the ionization efficiency, and the gas pressure is related to the size of the sample introduction capillary. When a capillary with an inner diameter of 0.25 mm and a length of 1 m (0.6 m horizontal section and 0.4 m horizontal section) is selected, the gas pressure inside the ionization source reaches 300 Pa, at which point the ionization efficiency is the highest.

[0058] To obtain the best analytical performance, the electrostatic lens voltage in this miniature ion trap mass spectrometer was optimized. The results showed that the ion focusing effect was optimal when the voltage of the conical aperture electrode was set to 10V, the voltage of the square aperture electrode was set to 8V, and the voltage of the ion trap front cap electrode was set to 9V.

[0059] The aforementioned miniature ion trap mass spectrometry, along with optimized parameters, was used to perform gradient measurements on benzene, toluene, ethyl sulfide, and methyl sulfide at specific concentration gradients. Quantitative curves for the four substances (benzene-a, toluene-b, ethyl sulfide-c, and methyl sulfide-d) were plotted, as shown below. Figure 2 As shown, Figure 2 In the figure, 'a' and 'b' are quantitative curves obtained by testing benzene and toluene gases at concentrations of 5, 10, 20, 40, 60, and 80 ppbv, respectively. The quantitative linearity coefficient R for benzene is... 2 The quantitative linearity coefficient R of toluene is 0.9909. 2 It is 0.9971. Figure 2 In the figure, c and d are quantitative curves obtained by testing ethyl sulfide and dimethyl sulfide gases at concentrations of 10, 20, 40, 60, 80, and 100 ppbv, respectively. The quantitative linearity coefficient R of ethyl sulfide is... 2 The quantitative linearity coefficient R for dimethyl sulfide is 0.9909. 2 The value is 0.9870, which shows that this miniature ion trap mass spectrometer has good quantitative analysis capabilities for four typical volatile organic compounds.

[0060] The miniature ion trap mass spectrometer in this embodiment has two modes: full scan and isolated scan. The isolated scan mode can improve the sensitivity of the instrument, such as... Figure 3 As shown in b, compared to full scan, the signal-to-noise ratio of benzene and toluene can be improved by approximately 10 to 15 times in isolated mode, and the detection limit of the instrument for benzene and toluene can reach 0.5 ppbv in this mode. Figure 3 As shown in 'a'.

[0061] In this embodiment, the resolution of the miniature ion trap mass spectrometer can be optimized by adjusting the scan speed, such as... Figure 4 As shown, at the optimal scanning speed, the instrument achieves a full width at half maximum (FWHM) of 0.354 for 60 ppbv benzene, with a resolution of 232.

[0062] In this embodiment, the miniature ion trap mass spectrometer uses a continuous atmospheric pressure interface with direct capillary injection, which offers better stability compared to traditional discontinuous atmospheric pressure interfaces. Figure 5 As shown, after 20 consecutive scans of 100 ppbv benzene standard gas, the signal intensity fluctuation was small, and the calculated relative standard deviation was 3.2%.

[0063] The miniature ion trap mass spectrometer in this embodiment uses a photoionization-induced chemical ionization ion source, which has soft ionization characteristics, is not prone to fragmentation, and facilitates substance identification. For example... Figure 6 As shown in Figure a, a mixture of OVOCs (Oxygen VOCs) at 100 ppbv, including acrolein (characteristic peak 57), acetone (characteristic peak 59), n-butyraldehyde (characteristic peak 71), butenal (characteristic peak 69), pentanal (characteristic peak 85), hexanal (characteristic peak 100), and m-methylbenzaldehyde (characteristic peak 119), was tested. The characteristic peaks of each substance in the spectrum were mostly molecular ion peaks, with virtually no fragmentation. A mixture of malodorous gases at 100 ppbv, including methyl acrylate (characteristic peak 86), ethyl acrylate (characteristic peak 100), dimethyl disulfide (characteristic peak 94), and ethyl acetate (characteristic peak 116), was also tested. The results showed that the characteristic peaks of these four substances were also mostly molecular ion peaks. Figure 6 As shown in b, very little fragmentation is generated.

[0064] Example 2

[0065] This embodiment provides an application method for the ion trap mass spectrometry system of the UAV used for tracing atmospheric volatile organic pollutants in Embodiment 1, including the following steps:

[0066] First, the concentration threshold of pollutants exceeding the standard in the polluted area is roughly determined. Then, the drone 20 takes off from a certain position downwind of the polluted scene, and the camera monitoring instrument 19 captures the surrounding scene in real time. The sample airflow first passes through the conical anti-vortex groove 17, which gradually stabilizes the airflow. At the same time, under the action of the detachable heat-conducting screen 16, most large particles are filtered out, and the airflow direction is also changed. Then, the gas enters the ion source chamber through the sample introduction capillary 4 on the ion trap mass spectrometer. The gas in the pipe is continuously heated by the heating device 18. The sample gas is ionized under the combined action of the radio frequency excitation VUV lamp 1, the repulsion electrode 2, the inlet electrode 3, and the segmental quadrupole radio frequency transmission electrode 5. The ionized sample is focused and transmitted into the ion trap mass analyzer 9 by the conical hole electrode 6, the square open hole electrode 7, and the ion trap front end cover electrode 8 for mass scanning. Finally, it bounces into the ion detector 11 to complete the mass analysis, thereby obtaining information such as the type and concentration of pollutants in the air. The UAV aerial survey platform uses a communication module to share the detection data with the ground control platform 21 in real time. The source tracing algorithm software installed on it plans the aerial survey route of the UAV 20 in real time and sends the instructions back to the UAV 20. This process is repeated until the pollution source is found.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone, characterized in that, Including UAV aerial survey platforms and ground control platforms; The ground control platform is equipped with traceability algorithm software and a communication module; The UAV aerial survey platform includes a UAV and a miniature ion trap mass spectrometer; the miniature ion trap mass spectrometer is connected to the UAV. The miniature ion trap mass spectrometer includes a sample introduction unit, a primary chamber, a secondary chamber, a vortex pump, and a molecular pump. The primary chamber and the secondary chamber are connected horizontally through a conical electrode. The molecular pump is connected to the secondary chamber through a gas extraction line, and the vortex pump is connected to both the molecular pump and the primary chamber through a gas extraction line. The sample introduction unit includes a conical anti-vortex groove and a sample introduction capillary; the central axis of the conical anti-vortex groove is parallel to the horizontal direction, and a detachable heat-conducting screen is installed inside it; the sample introduction capillary includes a horizontal section and a vertical section, one end of the horizontal section of the sample introduction capillary is connected to the bottom of the conical anti-vortex groove, and one end of the vertical section of the sample introduction capillary is connected to the primary cavity; a heating device is installed on the outside of the sample introduction capillary. The detachable heat-conducting screen is perpendicular to the central axis of the conical anti-vortex groove, and the outer ring of the detachable heat-conducting screen abuts against the conical anti-vortex groove. The conical anti-vortex groove changes the direction of fluid flow, causing the vortices caused by the airflow from the drone propeller to gradually dissipate, thus stabilizing the airflow. The primary chamber is provided with a radio frequency excitation VUV lamp, a repulsion electrode, an air intake electrode, and a segmental quadrupole radio frequency transmission electrode arranged sequentially in the direction extending toward the secondary chamber. The sample introduction capillary extends radially perpendicular to the radio frequency excitation VUV lamp to the central hole inside the air intake electrode. The central hole diameter of the air intake electrode gradually increases in the direction extending toward the secondary chamber.

2. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 1, characterized in that, The diameter of the detachable heat-conducting screen is 1 / 3 to 2 / 3 of the top diameter of the conical anti-vortex groove.

3. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 1, characterized in that, The applied voltage of the repulsion electrode is greater than the applied voltage of the intake electrode, and the voltage difference between the two is less than 10V; a pair of radio frequency AC voltages with a frequency of 2.3 MHz, a peak-to-peak value adjustable from 0 to 500 V, and a phase difference of 180° are applied radially to the segment quadrupole radio frequency transmission electrode, and two voltage levels with a gradient decreasing along the direction extending toward the secondary cavity are applied axially, with the voltage difference between the two voltage levels being less than 10V.

4. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 1, characterized in that, The secondary cavity is provided with a square-aperture electrode, an ion trap front cover electrode, an ion trap mass analyzer, and an ion trap rear cover electrode in sequence along the horizontal direction away from the primary cavity.

5. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 4, characterized in that, The cone-shaped electrode and the square-shaped electrode are spaced 2-3 mm apart, and the square-shaped electrode and the front cover electrode of the ion trap are spaced 2-3 mm apart. The cone-shaped electrode, the square-shaped electrode, and the front cover electrode of the ion trap form an electrostatic lens structure.

6. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 4, characterized in that, The secondary cavity is also equipped with an ion detector, which is an electron multiplier. The central axis of the ion detector is perpendicular to the central axis of the ion trap mass analyzer. The central hole of the ion detector is coaxial with the slit of the ion trap mass analyzer. The ion detector and the ion trap mass analyzer are 5-10 mm apart.

7. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 6, characterized in that, The ion trap mass analyzer is a hyperboloid linear ion trap, with a pair of adjustable radio frequency voltages of 1.09 MHz and peak-to-peak value of 0~5000 V applied to its Y electrode; a pair of adjustable auxiliary radio frequency voltages of 235 kHz and peak-to-peak value of 0~20 V with a phase difference of 180° applied to its X electrode; and a voltage of -1400~-1800 V applied to the ion detector.

8. The ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using a drone as described in claim 1, characterized in that, The drone is a multi-rotor transport drone. The drone's fuselage integrates a communication module and a GPS module. The communication module is used to transmit the detection data of the miniature ion trap mass spectrometer to the ground control platform. The miniature ion trap mass spectrometer is fixed to the underside of the drone fuselage by sheet metal. The drone is equipped with a camera monitoring device.

9. The application method of the ion trap mass spectrometry system for tracing atmospheric volatile organic pollutants using an unmanned aerial vehicle (UAV) as described in any one of claims 1 to 8, characterized in that, Includes the following steps: When conducting source tracing tasks, the concentration threshold of atmospheric volatile organic pollutants is first input into the source tracing algorithm software on the ground control platform. Then, a drone takes off from a certain location downwind of the polluted area. During the flight, the drone monitors atmospheric volatile organic pollutants in real time using a miniature ion trap mass spectrometer. The detection data from the miniature ion trap mass spectrometer is then transmitted back to the ground control platform via a communication module. The source tracing algorithm software on the ground control platform plans the drone's flight route in real time based on the detection data from the miniature ion trap mass spectrometer and issues flight commands to the drone through communication equipment until the pollution source is found and the source tracing task is completed.

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