CN103426712A - Aerosol mass spectrometer with particle size selection - Google Patents

Abstract

This book applies for an aerosol mass spectrometer that can simultaneously detect the particle size, concentration and chemical composition of atmospheric aerosols. The aerosol mass spectrometer uses sampling holes with a diameter of about 100 microns to directly sample aerosols in the natural environment; aerosols The particles are focused into a particle beam with a diameter of about 0.5mm by the pneumatic focusing lens; the aerosol particles are selected by a particle size selector; the particle size selector is composed of three coaxial turntables with slits; the turntable of the particle size selector Driven by a synchronous motor; the frequency of the synchronous motor power supply is continuously adjustable; the aerosol particles selected by the particle size selector are gasified by a high-temperature (600-700°C) gasifier; the gasified gas is ionized by an electron impact ionizer; The generated ions are detected by a W-type reflective mass spectrometer, that is, the mass spectrum of the aerosol is obtained. The particle size, concentration and chemical composition of the organic aerosol can be obtained by analyzing the sampling rate, the frequency of the synchronous motor power supply and the obtained mass spectrum.

Description

Particle size selective aerosol mass spectrometer

Technical field

The invention relates to a particle diameter selective aerosol mass spectrometer, which can measure the particle diameter, concentration and chemical composition of atmospheric aerosol particles online. the

Background technique

In recent years, aerosol pollution has become the main form of air pollution in large and medium-sized cities in my country. Aerosol pollution not only endangers the health of citizens, but also affects the image of the city, traffic and many other aspects. With the economic growth and the improvement of people's living standards, the monitoring and control of aerosol pollution has become a primary issue in the urban environment. The chemical composition of atmospheric aerosol is very complex, it contains various trace metals, inorganic oxides, sulfates, nitrates, hydrocarbons and oxygen-containing organic compounds. The traditional aerosol composition analysis method is to use a collector to collect the aerosol, and then use an analytical instrument (such as HPLC/MS or GC/MS) to analyze the chemical composition of the aerosol. This process usually takes a long time (several hours to weeks). Although this method has accumulated a large amount of data for aerosol research, it cannot comprehensively obtain information on the change of aerosol chemical composition over time, and cannot find an effective theoretical basis for controlling aerosol pollution. At the same time, aerosol pollutants with different particle sizes have different degrees of harm to the human body and the environment. Therefore, the traditional aerosol component analysis methods can no longer meet people's needs for aerosol detection and analysis. the

Aerosol mass spectrometry technology matured at the end of the last century. The main inventors of the two main technical routes are Professor Kimberly A. Prather of the University of California, San Diego and Dr. John Jayne of Aerodyne. Professor Kimberly A. Prather invented an aerosol mass spectrometer based on laser desorption ionization technology, which uses two continuous laser beams to obtain aerosol particle size information, plus a pulsed laser beam (wavelength 266 nm) to vaporize aerosol and ionize to generate ions , and then use a reflection mass spectrometer to detect ion signals. This instrument is the prototype of TSI's 3800 aerosol time-of-flight mass spectrometer; Dr. John T. Jayne and others invented an aerosol mass spectrometer based on thermal vaporization-electron impact ionization technology, That is Aerodyne's aerosol mass spectrometer, which uses a high-speed turntable similar to a chopper to obtain aerosol particle size information, and then vaporizes the aerosol by a hot surface, then detects the chemical composition of the aerosol by electron impact ionization and a quadrupole mass spectrometer . This instrument uses a single turntable combined with a mass spectrometry data matrix to analyze the correspondence between particle size and mass spectrometry. The structure is relatively simple, but the data is stored in the form of a matrix. Analysis also takes a lot of time. At present, there are more than one hundred scientific research institutes or universities using TSI and Aerodyne aerosol time-of-flight mass spectrometers. In addition, there are many various aerosol mass spectrometers assembled by researchers themselves, such as aerosol mass spectrometers that use vacuum ultraviolet light as an ionization source. the

Aerosol mass spectrometers with different technical routes have different characteristics. Aerosol mass spectrometers based on electron impact ionization technology can analyze most inorganic and organic substances, and can perform quantitative analysis, but cannot gasify refractory substances such as carbon dioxide silicon etc. The aerosol mass spectrometer based on laser analysis and ionization technology can analyze/ionize all substances, and can be used to study refractory particles such as sand and dust. It has high sensitivity and has obvious advantages in analyzing metal elements in aerosols. Its disadvantage is quantitative measurement. Performance is poor. At present, there is a certain commercial market for aerosol mass spectrometers based on these two technologies. the

Contents of the invention

In order to overcome the shortcomings of existing aerosol mass spectrometers in particle size measurement, the present invention combines various advanced technologies in aerosol mass spectrometry research to provide a new aerosol mass spectrometer. The aerosol mass spectrometer adopts microhole sampling and aerodynamic focusing lens particle focusing technology, turntable particle size selector technology, high temperature gasification technology, electron collision technology and W-type double reflection ion detection technology. the

The technical scheme adopted by the patent of the present invention is: 1. Aerosol particles are directly sucked into the instrument by a micropore with a diameter of about 100 μm in the atmospheric environment; 2. The aerosol particles sucked into the instrument are accelerated and focused by the pneumatic focusing lens to form a diameter The particle beam of 0.5 mm is incident into the vacuum chamber; 3. Then the particle flow meets the particle size selector of the turntable. Due to the limitation of the rotating speed of the turntable and the distance and included angle between the turntable, only particles within a certain particle size range are allowed each time. Can pass through the slit of the particle size selector; 4. The turntable particle size selector is driven by a synchronous motor; 5. The speed of the synchronous motor is controlled by the frequency of the synchronous motor power supply; 6. The frequency of the synchronous motor power supply is continuously adjustable; 7. The selectively passing aerosol particles hit the high-temperature surface of the gasifier and are then gasified; 8. The gasified gas is ionized by a 70eV electron impact ionizer; 9. The generated ions are detected by a W-type reflective mass spectrometer ; 10. The particle size, concentration and chemical composition of aerosol particles can be analyzed and obtained by the sampling rate, synchronous motor frequency and mass spectrometry. the

The beneficial effect of the present invention is that the direct sampling of the aerosol in the air realizes the one-to-one correspondence between the particle size and the mass spectrum, which greatly reduces the storage capacity of data and the difficulty of analysis, improves the efficiency of instrument use, and reduces the cost of instrument use , can simultaneously detect the particle size, concentration and chemical composition of aerosol particles in the atmosphere, so as to effectively analyze and detect atmospheric aerosols. the

Description of drawings

Fig. 1 is an appearance diagram of the structure of the present invention, which is divided into four parts: 1. beam source chamber, 2. particle size measurement chamber, 3. gasification ionization chamber, and 4. W-type reflective mass spectrometry device. the

Fig. 2 is the cross-sectional structural drawing of the present invention, and main components have: 5. Sampling hole, 6. Globe valve, 7. Pneumatic focus lens group, 8. Particle size selector front turntable, 9. Particle size selector middle turntable, 10 .Particle size selector rear turntable, 11. Motor drive combination, 12. Micro synchronous motor, 13. Electron impact ionizer, 14. High temperature gasifier, 15. Ion migration electrode plate combination, 16. Ion extraction acceleration electrode plate combination , 17. High electric field strength ion mirror, 18. Low electric field strength ion mirror, 19. Microchannel plate ion detector, 20, 21, 22. Molecular pumps. the

Detailed ways

The main part of the particle size selective aerosol mass spectrometer is composed of four parts: a beam source chamber (1), a particle size measurement chamber (2), a gasification ionization chamber (3) and a W-type reflective mass device (4). The specific implementation method is: one, the aerosol is directly inhaled from the atmosphere by a sampling hole (5) with a diameter of about 100 microns; two, the stop valve (6) can control sampling or not; three, then the aerosol particles enter the aerodynamic focusing lens group (7), the aerodynamic focus lens group is made up of a series of 2-5mm aperture discs, and in the aerodynamic focus lens group, the aerosol particles are accelerated and focused to form an aerosol particle flow with a diameter of about 0.5 mm; four, the aerosol particles from The small hole between the beam source chamber (1) and the particle size measurement chamber (2) enters the particle size measurement chamber (2), and meets the particle size selector in the particle size measurement chamber. The particle size selector consists of a slit The turntable (8, 9, 10), the motor transmission combination (11) and a micro synchronous motor (12), due to the limitation of the rotating speed of the turntable and the distance and angle between the turntable, only particles within a certain particle size range can be Particles can pass through the slit of the particle size selector; 5. The speed of the synchronous motor is controlled by the frequency of the power supply of the synchronous motor. The frequency of the power supply of the synchronous motor is continuously adjustable, and there is a one-to-one correspondence between the speed of the synchronous motor and the particle size; 6. , The aerosol particles that selectively pass through the small hole between the particle size measurement chamber (2) and the gasification ionization chamber (3) enter the gasification ionization chamber (3), and then the aerosol particles hit the high temperature gasifier ( 13) is gasified, and the gas after gasification is ionized by the electron impactor (14) immediately; 7. The formed ions are detected by the W-type reflective mass spectrometer (4) to obtain the mass spectrum of the aerosol, which is processed and analyzed After that, the particle size, concentration and chemical composition information of organic aerosol particles can be obtained. the

Claims (10)

1. particle diameter selects aerosol mass spectrometer to be comprised of electron gun chamber, grain diameter measurement chamber, gasification ionization chamber and the reflective mass spectrometric apparatus of W type.It is characterized in that the electron gun chamber, grain diameter measurement chamber, gasification ionization chamber are connected successively with the reflective mass spectrometric apparatus of W type, between between electron gun chamber and grain diameter measurement chamber and grain diameter measurement chamber and gasification ionization chamber, have aperture to be connected, the reflective mass spectrometric apparatus of W type and electron gun chamber, grain diameter measurement chamber, the ionization chamber that gasifies are parallel.In the electron gun chamber, the pneumatic focus lens group of aerosol is installed, the particle diameter selector is housed in the grain diameter measurement chamber, in the gasification ionization chamber, high temperature gasifier and electron impact ionization device are housed.The electron gun chamber, the grain diameter measurement chamber, all be connected with molecular pump on gasification ionization chamber and the reflective mass spectrometric apparatus of W type, and molecular pump is connected with membrane pump.

2. particle diameter according to claim 1 is selected aerosol mass spectrometer, and it is characterized in that: atmospheric aerosol is not treated, and directly the thieff hatch by 100 microns of diameters enters into the electron gun chamber.

3. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: in Sample Room, by pneumatic focus lens group, aerosol particle is focused on.

4. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: in the grain diameter measurement chamber, the particle diameter selector is installed.

5. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: three coaxial turntables with slit that the particle diameter selector is driven by small synchronous motor form.

6. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: the supply frequency that small synchronous motor drives is continuously adjustable.

7. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: in the gasification ionization chamber, high temperature gasifier is installed.

8. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: in the gasification ionization chamber, the electron impact ionization device is installed.

9. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: ion is surveyed by the reflective mass spectrometric apparatus of W type.

10. particle diameter according to claim 1 is selected aerosol mass spectrometer, it is characterized in that: the reflective mass spectrometric apparatus of W type and electron gun chamber, grain diameter measurement chamber, the ionization chamber that gasifies are parallel.

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