Tracing unmanned aerial vehicle ion trap mass spectrum system for atmospheric volatile organic pollutants and application method of tracing unmanned aerial vehicle ion trap mass spectrum system

Abstract

The invention discloses an atmospheric volatile organic pollutant traceability unmanned aerial vehicle ion trap mass spectrum system and an application method thereof, and belongs to the technical field of pollutant traceability monitoring. The system provided by the invention 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, and the miniature ion trap mass spectrometer comprises a sample introduction unit, a primary cavity, a secondary cavity, a vortex pump and a molecular pump; the sample introduction unit comprises a conical vortex-proof groove and a sample introduction capillary tube; a detachable heat-conducting screen is arranged in the conical vortex-preventing groove; and a heat tracing device is arranged on the outer side of the sample injection capillary tube. According to the system provided by the invention, the unmanned aerial vehicle with high flexibility and high maneuverability is combined with the micro ion trap mass spectrum with relatively strong detection capability on volatile organic compounds for the first time, analysis and traceability of various volatile pollutants can be completed, and the system has high flexibility, high stability and high detection precision.

Description

Technical Field

[0001] The present invention relates to the technical field of pollutant source tracing monitoring, and in particular to an atmospheric volatile organic pollutant source tracing unmanned aerial vehicle ion trap mass spectrometry system and an application method thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance the understanding of the overall background of the invention and should not be necessarily regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Volatile organic compounds are ubiquitous in the atmospheric environment. They are of various types and change rapidly in time and space. Volatile organic compounds have a significant impact on human health and ambient air. On the one hand, many volatile organic compounds have toxic properties, and direct inhalation by the human body can cause various diseases. On the other hand, they are also important precursors for the formation of ozone and secondary organic aerosols, which in turn cause ozone pollution, photochemical smog and other malignant environmental pollution events. For the problem of volatile organic compound pollution, source tracing monitoring is the key.

[0004] For a long time, the source tracing monitoring technology for gas pollution has mainly been based on robots / robot dogs equipped with sensors for ground search. However, due to the complexity of the ground environment, the search coverage of robots / robot dogs is small, and the positioning speed is also slow. Due to their ultra-high flexibility and maneuverability, drones can conduct multi-level and multi-dimensional searches. In recent years, they have also been developed for emergency source tracing detection of atmospheric pollutants. At present, the technology that has been studied more is based on drones equipped with odor sensors, wind direction sensors, gas sensors and other sensor equipment combined with tracing algorithms for aerial tracing. This technology is called active olfactory technology. However, for a wide variety of volatile organic compounds, the performance and material detection range of sensors are very limited. When using drones for source tracing detection, it is not possible to obtain comprehensive pollution information from the pollution source.

[0005] At present, the research on portable mass spectrometry technology for volatile organic compound detection has become a hot topic in recent years. Among them, micro ion trap mass spectrometry has great application potential in the field of volatile organic compound traceability monitoring due to its small size, high working gas pressure and cascade mass spectrometry analysis capability of a single analyzer.

[0006] Graham R. Cooks' team at Purdue University has been committed to the miniaturization of ion trap mass spectrometry. They proposed a discontinuous atmospheric pressure interface, breaking the constraints of the vacuum pump group on the miniaturization of mass spectrometry, and developed a handheld first-stage vacuum micro-ion trap mass spectrometer combined with atmospheric pressure ionization to achieve the detection of multiple compounds. However, the portable ion trap mass spectrometer with a discontinuous atmospheric pressure interface cannot meet the quantitative requirements of volatile organic compounds due to the drastic changes in air pressure. In addition, the pinch valve used in the discontinuous atmospheric pressure interface realizes the ion injection instrument by compressing the elastic silicone rubber tube, and the long-term robustness of the instrument is poor. Xu Wei's team at Beijing Institute of Technology used capillary injection to develop a new type of second-stage differential vacuum micro-ion trap mass spectrometer with a continuous atmospheric pressure interface, which improved the stability and robustness of the instrument. In addition, the instrument introduced an ion funnel to focus ions in the first stage of vacuum to improve the ion transmission efficiency and obtain a toluene detection limit of 10ppbv. However, for the micro-ion trap mass spectrometer used for volatile organic compound source tracking and monitoring, the ion funnel assembly is complex and there is a low-mass discrimination problem, and compounds with a mass-to-charge ratio lower than 100Da are difficult to detect. Li Haiyang's team from the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, built a two-stage vacuum differential ion trap mass spectrometer system and tried to use a hexapole for ion transmission and focusing at 100Pa in the first-stage differential vacuum system, achieving highly sensitive qualitative and quantitative analysis of volatile organic compounds, with a toluene detection limit of 1ppbv while maintaining high stability. However, the instrument is currently mainly used for short-distance ground source tracking monitoring of pollution sources.

[0007] At present, there is no existing technology that combines a portable ion trap mass spectrometer with a drone. Since drones need to start and stop, ascend and descend, accelerate and decelerate in the air during the process of tracing pollutants, changes in airflow will reduce the detection stability of the portable ion trap mass spectrometer, resulting in inaccurate detection results. Therefore, how to provide a drone ion trap mass spectrometer 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 atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system and an application method thereof. The system can comprehensively monitor and trace the 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 atmospheric volatile organic pollutant tracing UAV ion trap mass spectrometry system, including a UAV aerial survey platform and a ground control platform;

[0010] The ground control platform is equipped with tracing algorithm software and communication modules;

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

[0012] The micro ion trap mass spectrometer comprises a sample injection unit, a primary cavity, a secondary cavity, a vortex pump and a molecular pump; the primary cavity and the secondary cavity are connected in the horizontal direction through a conical hole electrode, the molecular pump is connected to the secondary cavity through an exhaust pipeline, and the vortex pump is connected to the molecular pump and the primary cavity through the exhaust pipeline respectively;

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

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

[0015] Preferably, a radio frequency excitation VUV lamp, a repeller electrode, an air inlet electrode and a segment quadrupole radio frequency transmission electrode are sequentially arranged in the first-level cavity in the direction extending toward the second-level cavity; the injection capillary radially extends to the center hole inside the air inlet electrode perpendicular to the radio frequency excitation VUV lamp; the center aperture of the air inlet electrode gradually increases in the direction extending toward the second-level cavity.

[0016] Furthermore, the applied voltage of the repeller 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 RF AC voltages with a frequency of 2.3MHz, an adjustable peak-to-peak value of 0-500V, and a phase difference of 180° are applied in the radial direction of the segmented quadrupole RF transmission electrode, and two-level voltages with decreasing gradients in the direction extending toward the secondary cavity are applied axially, and the voltage difference between the two levels is less than 10V.

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

[0018] Furthermore, the conical hole electrode and the square hole electrode are 2 to 3 mm apart, the square hole electrode and the ion trap front end cover electrode are 2 to 3 mm apart, and the conical hole electrode, the square hole electrode and the ion trap front end cover electrode constitute an electrostatic lens structure.

[0019] Furthermore, an ion detector is also arranged 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 is 5 to 10 mm away from the ion trap mass analyzer.

[0020] Furthermore, the ion trap mass analyzer is a hyperbolic linear ion trap, and its Y electrode applies a pair of RF voltages with a frequency of 1.09 MHz and a peak-to-peak value of 0 to 5000 V, which are adjustable for ion capture; the X electrode applies a pair of auxiliary RF voltages with a frequency of 235 kHz, a peak-to-peak value of 0 to 20 V, and an adjustable phase difference of 180°, which are used to eject ions; the ion detector applies a voltage of -1400 to -1800 V, which is used to receive ions ejected from the ion trap mass analyzer, and realize amplified detection of ion signals.

[0021] Preferably, the UAV is a multi-rotor carrier UAV, a communication module and a GPS module are integrated inside the fuselage of the UAV, and the communication module is used to transmit the detection data of the micro ion trap mass spectrometer to the ground control platform.

[0022] Preferably, the micro ion trap mass spectrometer is fixed to the bottom of the drone body by sheet metal, and the drone is equipped with a camera monitor.

[0023] In a second aspect, the present invention provides an application method of the above-mentioned atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system, comprising the following steps:

[0024] When performing a source tracing mission, the concentration threshold of atmospheric volatile organic pollutants is first entered into the source tracing algorithm software of the ground control platform, and then the UAV is launched at a certain location downwind in the polluted area. During the flight, the UAV monitors the atmospheric volatile organic pollutants in real time through a micro ion trap mass spectrometer, and then transmits the detection data of the micro ion trap mass spectrometer back to the ground control platform through the communication module. The source tracing algorithm software on the ground control platform plans the UAV's navigation route in real time according to the detection data of the micro ion trap mass spectrometer, and sends navigation instructions to the UAV through the communication equipment until the pollution source is found and the source tracing mission is completed.

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

[0026] (1) The present invention combines for the first time a highly flexible and highly maneuverable drone with a miniature ion trap mass spectrometer that has a strong ability to detect volatile organic compounds. Compared with the traditional traceability system of drones + multiple sensors, this system only requires one mass spectrometer to complete the analysis of multiple volatile pollutants. While simplifying the traditional traceability system architecture, it broadens the application scenarios of volatile organic compound traceability. 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 propeller airflow of the UAV on the mass spectrometer sampling, the present invention designs a unique air intake processing device, and adds a conical anti-vortex groove at the sampling inlet of the mass spectrometer, which can change the flow direction of the fluid, so that the vortex gradually dissipates, realizes the stability of the airflow, and thus ensures the stable collection of samples.

[0028] (3) The injection unit of the present invention is equipped with a detachable heat-conductive screen and a heating device, wherein the heating device can heat the injection capillary, thereby heating and volatilizing the non-volatile components, effectively avoiding the problem of instrument contamination during long-term operation of the system; the mesh of the detachable heat-conductive screen can change the injection direction of the airflow during the injection process, so that the injection airflow tends to be stable, and it can also play a role in screening 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 surface of the screen, realizing self-cleaning during the operation process, and avoiding injection blockage; it can be removed from the conical anti-vortex groove for subsequent cleaning; the above-mentioned arrangement further enhances the stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute an improper limitation of the present invention. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 Schematic diagram of the structure of the atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system according to Example 1 of the present invention;

[0031] Figure 2 This is a quantitative analysis test of multiple volatile organic compounds by a micro ion trap mass spectrometer in the atmospheric volatile organic pollutant source tracing drone ion trap mass spectrometer system of Example 1 of the present invention; wherein a is benzene, b is toluene, c is ethyl sulfide, and d is methyl sulfide;

[0032] Figure 31 is the scanning result of benzene and toluene by the micro ion trap mass spectrometer in the atmospheric volatile organic pollutant source tracing drone ion trap mass spectrometer system of Example 1 of the present invention, wherein a is the scanning spectrum in the isolated mode, and b is the signal-to-noise ratio comparison diagram of benzene and toluene in the isolated mode and the full scanning mode;

[0033] Figure 4 The micro ion trap mass spectrometer in the atmospheric volatile organic pollutant source tracing drone ion trap mass spectrometer system of Example 1 of the present invention is tested on 60 ppbv benzene standard gas and then the resolution test result is obtained by Gaussian fitting;

[0034] Figure 5 The micro ion trap mass spectrometer in the atmospheric volatile organic pollutant source tracing drone ion trap mass spectrometer system of Example 1 of the present invention continuously scans 100 ppbv benzene standard gas 20 times to obtain the stability test result;

[0035] Figure 6 It is a scanning spectrum of a mixed volatile gas with a concentration of 100 ppbv by a micro ion trap mass spectrometer in the atmospheric volatile organic pollutant source tracing drone ion trap mass spectrometry system of Example 1 of the present invention, wherein the mixed gas in a is acrolein (characteristic peak 57), acetone (characteristic peak 59), n-butyraldehyde (characteristic peak 71), crotonaldehyde (characteristic peak 69), valeraldehyde (characteristic peak 85), hexanal (characteristic peak 100), and m-methylbenzaldehyde (characteristic peak 119); the mixed gas in b is methyl acrylate (characteristic peak 86), ethyl acrylate (characteristic peak 100), dimethyl disulfide (characteristic peak 94), and ethyl acetate (characteristic peak 116);

[0036] In the figure: the distances or sizes between the parts are exaggerated to show the positions of the parts, and the schematic diagram is for illustration only;

[0037] Among them, 1. RF excitation VUV lamp; 2. repeller electrode; 3. air inlet electrode; 4. sample injection capillary; 5. fragment quadrupole RF transmission electrode; 6. conical hole electrode; 7. square opening electrode; 8. ion trap front end cover electrode; 9. ion trap mass analyzer; 10. ion trap rear end cover electrode; 11. ion detector; 12. molecular pump; 13. vortex pump; 14. primary cavity; 15. secondary cavity; 16. detachable thermal conductive screen; 17. conical anti-vortex groove; 18. heating device; 19. video monitoring instrument; 20. UAV; 21. ground control platform. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0039] As introduced in the background technology, the current tracing detection technology for volatile organic compounds mainly uses robots or robot dogs carrying sensors for detection on the ground side, and the flexibility and maneuverability of robots / dogs are very limited, so the scope of their tracing applications depends largely on the environment in which they are located. Aerial tracing mainly uses drones equipped with gas sensors, but the performance of gas sensors is often poor and the detection substances are single, which limits the application scope of the system. Therefore, the present invention proposes to combine a high-performance mass spectrometer with a highly flexible and maneuverable drone to provide an atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system and its application method. The whole system has established a complete tracing system, which can accurately and quickly detect pollution sources in various complex environments. The system has great potential in the tracing detection of volatile organic compounds.

[0040] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0041] Example 1

[0042] This embodiment provides an atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system, see Figure 1 , including a UAV aerial survey platform and a ground control platform 21.

[0043] The drone aerial survey platform includes a drone 20 and a micro ion trap mass spectrometer, which is fixed to the bottom of the drone 20 by sheet metal, and is equipped with a video monitor 19. The video monitor 19 is used to capture the surrounding images of the drone 20 in real time, and the micro ion trap mass spectrometer is used to monitor the pollutants around the drone 20 in real time and determine the material information (including material type, concentration, etc.) of volatile organic compounds in the atmosphere.

[0044] The drone 20 is preferably a multi-rotor carrier drone 20, and a communication module and a GPS module are integrated inside the fuselage of the drone 20, wherein the communication module is used to transmit the detection data of the micro ion trap mass spectrometer to the ground control platform 21, and the GPS module is used to accurately locate the position of the drone 20. The communication module and the GPS module are integrated inside the fuselage of the drone 20 to prevent signal interference and avoid affecting communication and positioning.

[0045] The micro ion trap mass spectrometer includes a sample injection unit, a primary cavity 14, a secondary cavity 15, a vortex pump 13 and a molecular pump 12; the primary cavity 14 and the secondary cavity 15 are connected in the horizontal direction through a conical electrode 6, the molecular pump 12 is connected to the secondary cavity 15 through an exhaust pipeline, and the vortex pump 13 is respectively connected to the molecular pump 12 and the primary cavity 14 through an exhaust pipeline. The vortex pump 13 is mainly used to maintain the working gas pressure of the ion source in the primary cavity 14 and the working gas pressure of the molecular pump 12, and 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 cavity 15.

[0046] The sampling unit includes a conical anti-vortex groove 17 and a sampling capillary 4; the central axis of the conical anti-vortex groove 17 is parallel to the horizontal direction, and this setting is for the convenience of sampling; a detachable heat-conducting screen 16 is arranged inside it. The conical anti-vortex groove 17 is preferably a conical anti-vortex groove. The conical anti-vortex groove 17 can change the flow direction of the fluid, so that the vortex caused by the propeller airflow of the drone 20 gradually dissipates, and the airflow is stabilized, thereby ensuring the stable collection of samples. The material of the conical anti-vortex groove 17 is an alloy material with an anti-corrosion adsorption treatment on the surface, and its aperture gradually decreases from the outside to the inside, thereby gradually reducing the strength of the vortex, so that the airflow is stable.

[0047] The detachable heat-conductive screen 16 is perpendicular to the central axis of the conical anti-vortex groove 17, the outer ring of the detachable heat-conductive screen 16 is against the conical anti-vortex groove 17, and the diameter of the detachable heat-conductive screen 16 is 1 / 3 to 2 / 3 of the top diameter of the conical anti-vortex groove 17, so as to give full play to the airflow stabilization effect of the conical anti-vortex groove 17 and the detachable heat-conductive screen 16 at the same time. The detachable heat-conductive screen 16 is woven from metal wire, which can change the injection direction of the airflow during the injection process, so that the injection airflow tends to be stable, and it can also play the role of screening out large-particle floating pollutants. In addition, the detachable heat-conductive screen 16 can also be connected to a heating device (not shown in the figure), and its excellent thermal conductivity can promote the volatilization of non-volatile substances on the surface of the screen and provide a preheating environment for the intake air; it can be removed from the conical anti-vortex groove 17 for subsequent cleaning.

[0048] Since the cavity is a vacuum environment, the gas can be self-absorbed into the micro ion trap mass spectrometer through the sampling capillary 4. The sampling capillary 4 includes a horizontal section and a vertical section. One end of the horizontal section of the sampling capillary 4 is connected to the bottom of the conical anti-vortex groove 17, and one end of the vertical section of the sampling capillary 4 is connected to the primary cavity 14. A heating device 18 is arranged on the outside of the sampling capillary 4, and its main body is composed of a heating pipe, which is directly wrapped around the periphery of the mass spectrometer inlet capillary, so that the internal temperature of the capillary can reach 180°. On the one hand, it prevents volatile pollutants from being adsorbed on the capillary wall, and on the other hand, some components that are less volatile can also be heated and volatilized, so as to enter the cavity and be ionized. Preferably, the inner diameter of the sampling capillary 4 is 0.2-0.3 mm.

[0049] A radio frequency excitation VUV lamp 1, a repeller electrode 2, an inlet electrode 3 and a segment quadrupole radio frequency transmission electrode 5 are sequentially arranged in the direction extending from the primary cavity 14 to the secondary cavity 15. The radio frequency excitation VUV lamp 1, the repeller electrode 2, the inlet electrode 3 and the segment quadrupole radio frequency transmission electrode 5 are coaxially placed along the central axis, and the four are integrated through supporting fixtures to form a photochemical ionization source. After the sample is ionized, the ions are focused by the transmission of the segment quadrupole radio frequency transmission electrode 5 and enter the conical hole electrode 6. The sample injection capillary 4 is perpendicular to the radio frequency excitation VUV lamp 1 and radially extends into the central hole of the inlet electrode 3.

[0050] The air inlet electrode 3 divides the ionization zone into a photoionization zone and a chemical ionization zone, and its central aperture gradually increases along the direction extending to the secondary cavity 15. Preferably, the central aperture of the air inlet electrode 3 is expanded from 3mm to 6mm, and the repelling electrode 2 is a circular electrode with a central opening of 6mm; the voltage applied by the repelling electrode 2 is greater than the voltage applied by the air inlet electrode 3, and the pressure difference between the two is 0-10V.

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

[0052] The present invention combines a photochemical ionization source dominated by a radio frequency excitation VUV lamp 1 and a fragment quadrupole radio frequency transmission electrode 5 with an ion trap. Through the higher light flux of the radio frequency excitation VUV lamp 1, the collision focusing of the radial radio frequency of the fragment quadrupole radio frequency transmission electrode 5 and the efficient transmission of the axial gradient direct current, combined with the ability of the ion trap to accumulate and capture ions, highly sensitive detection and analysis of volatile organic compounds can be achieved, and the detection limit can reach 0.5ppbv, which can effectively reduce the difficulty of the traceability task and greatly improve the accuracy of the system traceability.

[0053] A square hole electrode 7, an ion trap front end cover electrode 8, an ion trap mass analyzer 9 and an ion trap rear end cover electrode 10 are sequentially arranged in the secondary cavity 15 along the horizontal direction away from the primary cavity 14. The three electrodes, the cone hole electrode 6, the square hole electrode 7 and the ion trap front end cover electrode 8, form an electrostatic lens structure, wherein the cone hole electrode 6 is the front electrode with a central opening of 0.4 mm, and is also used to connect two vacuum cavities to achieve vacuum differential; the central electrode is a square hole electrode 7 with a central opening of 3 mm, and the rear electrode is fixed by screws at 2 to 3 mm in front of the ion trap mass analyzer 9, and is also used as the ion trap front end cover electrode 8, with a central opening of 2 mm. The three electrodes are 2 to 3 mm apart from each other, and are used to focus the sample ions and introduce them into the ion trap mass analyzer 9.

[0054] The ion trap mass analyzer 9 is a hyperbolic linear ion trap with a cross-sectional hyperbolic radius of 4mm and a trap length of 40mm. The left and right hyperbolic electrodes are provided with slits and are mounted on a ceramic fixture. The electrodes are integrated with the front and rear cover electrodes by screws and placed 2 to 3mm behind the front cover electrode 8 of the ion trap for mass analysis. The Y electrode of the ion trap mass analyzer 9 applies a pair of 1.09MHz frequency, 0-5000V adjustable peak-to-peak radio frequency voltages to achieve ion capture. When the peak-to-peak value of the working voltage is set to 300V, the ion trap has the highest ion capture efficiency. The X electrode applies a pair of 235kHz frequency, 0-20V adjustable peak-to-peak value, and 180° phase difference auxiliary radio frequency voltages to achieve ion ejection.

[0055] An ion detector 11 is also provided in the secondary cavity 15. The central axis of the ion detector 11 is perpendicular to the central axis of the ion trap mass analyzer 9. The ion detector 11 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 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 a screw. After optimization, the best detection effect is obtained when the distance between the two is 10 mm. The voltage of the ion detector 11 is related to its life and performance. In order to balance its performance and life, its voltage is finally set to -1700V. At this voltage, it can be used for a long time while having certain performance.

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

[0057] The micro ion trap mass spectrometer of this embodiment is tested and analyzed according to the optimal conditions selected above. The gas pressure in the mass spectrometer ionization source cavity is directly related to the ionization efficiency, and its gas pressure is related to the size of the injection capillary. When a capillary with an inner diameter of 0.25 mm and a length of 1 m (0.6 m in the horizontal section and 0.4 m in the horizontal section) is selected, the gas pressure in the ionization source reaches 300 Pa, at which time the ionization efficiency is the highest.

[0058] In order to obtain the best analytical performance, the electrostatic lens voltage in the micro ion trap mass spectrometer was optimized. The results showed that the ion focusing effect was best when the conical opening electrode voltage was set to 10V, the square opening electrode voltage was set to 8V, and the ion trap front cover electrode voltage was set to 9V.

[0059] The above-mentioned micro-ion trap mass spectrometer and optimized parameters were used to conduct gradient tests on benzene, toluene, ethyl sulfide and methyl sulfide with a certain concentration gradient, and the quantitative curves of the four substances (benzene-a, toluene-b, ethyl sulfide-c and methyl sulfide-d) were drawn, as shown in FIG. Figure 2 As shown, Figure 2 a and b are the quantitative curves obtained by testing benzene and toluene gases at concentrations of 5, 10, 20, 40, 60, and 80 ppbv, respectively. The quantitative linear coefficient of benzene is R 2 The quantitative linear coefficient of toluene is 0.9909. 2 is 0.9971. Figure 2 c and d in the figure are the quantitative curves obtained by testing 10, 20, 40, 60, 80, and 100 ppbv of ethyl sulfide and methyl sulfide gas respectively. The quantitative linear coefficient R 2 The quantitative linear coefficient of methyl sulfide is 0.9909. 2 It is 0.9870. It can be seen that the micro ion trap mass spectrometer has good quantitative analysis capabilities for four typical volatile organic compounds.

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

[0061] The micro-ion trap mass spectrometer in this embodiment can optimize the resolution by adjusting the scanning speed, such as Figure 4 As shown, at the optimal scanning speed, the half-peak width of 60 ppbv benzene can reach 0.354 and the resolution is 232.

[0062] In this embodiment, the micro ion trap mass spectrometer uses a continuous atmospheric pressure interface for capillary direct injection, which has better stability than the traditional discontinuous atmospheric pressure interface. Figure 5 As shown, when 100 ppbv benzene standard gas is scanned continuously for 20 times, the signal intensity fluctuates slightly, and the calculated relative standard deviation is 3.2%.

[0063] The micro-ion trap mass spectrometer in this embodiment uses a chemical ionization ion source triggered by photoionization, which has soft ionization characteristics, is not easy to generate fragments, and is convenient for substance identification. Figure 6 As shown in a, a 100 ppbv OVOCs mixed gas of acrolein (characteristic peak 57), acetone (characteristic peak 59), n-butyraldehyde (characteristic peak 71), crotonaldehyde (characteristic peak 69), valeraldehyde (characteristic peak 85), hexanal (characteristic peak 100), and m-methylbenzaldehyde (characteristic peak 119) was tested. The characteristic peaks of each substance in the spectrum are mostly molecular ion peaks, and there is basically no fragmentation phenomenon. A 100 ppbv malodorous mixed gas of methyl acrylate (characteristic peak 86), ethyl acrylate (characteristic peak 100), dimethyl disulfide (characteristic peak 94), and ethyl acetate (characteristic peak 116) was tested. The results show that the characteristic peaks of the four substances are also mostly molecular ion peaks, such as Figure 6 As shown in b, very little fragmentation is produced.

[0064] Example 2

[0065] This embodiment provides an application method of the atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system in Embodiment 1, comprising the following steps:

[0066] First, roughly determine the concentration threshold of pollutants in the polluted area. Then take off the drone 20 at a certain position downwind of the polluted scene, and the camera monitor 19 captures the nearby images in real time. The sample airflow first passes through the conical anti-vortex groove 17, so that the airflow gradually stabilizes. At the same time, under the action of the detachable heat-conducting screen 16, most large particles are filtered and the airflow direction is changed. Then the gas enters the ion source chamber through the injection capillary 4 on the ion trap mass spectrometer. The gas in the pipeline is continuously heated by the heating device 18. The sample gas is ionized under the joint action of the radio frequency excitation VUV lamp 1, the repeller electrode 2, the intake electrode 3 and the fragment quadrupole radio frequency transmission electrode 5. The ionized sample is focused and transmitted by the conical hole electrode 6, the square opening electrode 7 and the ion trap front cover electrode 8 into the ion trap mass analyzer 9 for mass scanning, and finally bounces to the ion detector 11 to complete the mass analysis, thereby obtaining information such as the substance 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 tracing algorithm software loaded 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 source of pollution is found.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An atmospheric volatile organic pollutant tracing drone ion trap mass spectrometry system, characterized in that: Including UAV aerial survey platform and ground control platform; The ground control platform is equipped with tracing algorithm software and communication modules; The UAV aerial survey platform includes a UAV and a micro ion trap mass spectrometer; the micro ion trap mass spectrometer is connected to the UAV; The micro ion trap mass spectrometer comprises a sample injection unit, a primary cavity, a secondary cavity, a vortex pump and a molecular pump; the primary cavity and the secondary cavity are connected in the horizontal direction through a conical hole electrode, the molecular pump is connected to the secondary cavity through an exhaust pipeline, and the vortex pump is connected to the molecular pump and the primary cavity through the exhaust pipeline respectively; The sampling unit comprises a conical anti-vortex groove and a sampling capillary; the central axis of the conical anti-vortex groove is parallel to the horizontal direction, and a detachable heat-conductive screen is arranged inside the conical anti-vortex groove; the sampling capillary comprises a horizontal section and a vertical section, one end of the horizontal section of the sampling capillary is connected to the bottom of the conical anti-vortex groove, and one end of the vertical section of the sampling capillary is connected to the primary cavity; a heating device is arranged on the outside of the sampling capillary.

2. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 1, characterized in that: The detachable heat-conductive screen is perpendicular to the central axis of the conical anti-vortex groove, the outer circle of the detachable heat-conductive screen is against the conical anti-vortex groove, and the diameter of the detachable heat-conductive screen is 1 / 3 to 2 / 3 of the top surface diameter of the conical anti-vortex groove.

3. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 1, characterized in that: A radio frequency excitation VUV lamp, a repeller electrode, an air intake electrode and a segment quadrupole radio frequency transmission electrode are sequentially arranged in the first-stage cavity in the direction extending toward the second-stage cavity; the sampling capillary is perpendicular to the radio frequency excitation VUV lamp and radially extends to the central hole inside the air intake electrode; the central aperture of the air intake electrode gradually increases in the direction extending toward the second-stage cavity.

4. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 3, 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 RF AC voltages with a frequency of 2.3MHz, an adjustable peak-to-peak value of 0-500V, and a phase difference of 180° are applied in the radial direction of the segmented quadrupole RF transmission electrode, and two-level voltages with a decreasing gradient in the direction extending toward the secondary cavity are applied in the axial direction, and the voltage difference between the two levels is less than 10V.

5. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 1, characterized in that: A square opening electrode, an ion trap front end cover electrode, an ion trap mass analyzer and an ion trap rear end cover electrode are sequentially arranged in the secondary cavity along a horizontal direction away from the primary cavity.

6. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 5, characterized in that: The conical hole electrode and the square hole electrode are 2-3 mm apart, and the square hole electrode and the ion trap front end cover electrode are 2-3 mm apart. The conical hole electrode, the square hole electrode and the ion trap front end cover electrode constitute an electrostatic lens structure.

7. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 5, characterized in that: The secondary cavity is also provided 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, and the ion detector is 5 to 10 mm away from the ion trap mass analyzer.

8. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 7, characterized in that: The ion trap mass analyzer is a hyperbolic linear ion trap, and its Y electrode applies a pair of 1.09MHz, 0-5000V adjustable RF voltages; the X electrode applies a pair of 235kHz, 0-20V adjustable auxiliary RF voltages with a phase difference of 180°; the ion detector applies a voltage of -1400 to -1800V.

9. The ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to claim 1, characterized in that: The UAV is a multi-rotor transport UAV, and a communication module and a GPS module are integrated inside the fuselage of the UAV. The communication module is used to transmit the detection data of the micro ion trap mass spectrometer to the ground control platform; the micro ion trap mass spectrometer is fixed under the UAV fuselage by sheet metal; and the UAV is equipped with a camera monitor.

10. The application method of the ion trap mass spectrometry system for tracing the source of atmospheric volatile organic pollutants according to any one of claims 1 to 9, characterized in that: The steps include: When performing a source tracing mission, the concentration threshold of atmospheric volatile organic pollutants is first entered into the source tracing algorithm software of the ground control platform, and then the UAV is launched at a certain location downwind in the polluted area. During the flight, the UAV monitors the atmospheric volatile organic pollutants in real time through a micro ion trap mass spectrometer, and then transmits the detection data of the micro ion trap mass spectrometer back to the ground control platform through the communication module. The source tracing algorithm software on the ground control platform plans the UAV's navigation route in real time according to the detection data of the micro ion trap mass spectrometer, and sends navigation instructions to the UAV through the communication equipment until the pollution source is found and the source tracing mission is completed.

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