Photoionization light intensity selectable quadrupole mass spectrometer and use method thereof

Abstract

The invention relates to a photoionization light intensity selectable quadrupole mass spectrometer and a use method thereof. The photoionization light intensity selectable quadrupole mass spectrometer comprises a light source cavity, a main cavity, a quadrupole mass analyzer, a photomultiplier, a molecular pump and a light intensity selection assembly. The light intensity selection assembly is used for selecting light intensity; the main cavity comprises an ionization chamber and an analysis chamber, an ion collimating lens for focusing ions formed by ionization is mounted in the ionization chamber, and the focused ions enter the analysis chamber through a through hole; the quadrupole rod mass analyzer is used for screening ions with different mass-to-charge ratios and sending the ions into the photomultiplier, the photomultiplier is used for amplifying an ion current signal and sending the ion current signal to the processor for processing, and the processor is used for detecting gas to be detected. The light intensity of the light beam entering the ionization chamber is selected through the light intensity selection assembly, flexible selection of the light intensity of photoionization is achieved, the complex operation of light intensity selection of a traditional photoionization mass spectrum system is greatly optimized, and the working efficiency of the mass spectrum system is greatly improved.

Description

Technical Field

[0001] This application relates to the field of mass spectrometry analysis technology, specifically a photoionization intensity selectable quadrupole mass spectrometer and its usage method. Background Technology

[0002] Volatile organic compounds (VOCs) are the main culprits in the formation of photochemical smog and ozone pollution, and are also substances that directly harm human health. VOCs are precise indicators for detecting pollution sources and are key contributors to ozone and PM2.5 pollution. Rapid and accurate detection of atmospheric VOC levels is of great significance for understanding the causes of pollution and for environmental remediation.

[0003] Mass spectrometry, as an important method for detecting VOCs, has been widely applied to all aspects of VOCs detection in the atmosphere. Currently, commonly used direct atmospheric pressure injection methods based on mass spectrometry for substance detection include pressure photoionization (APPI) and proton transfer mass spectrometry (PTR).

[0004] APPI, as a relatively soft ionization method, involves a gas entering the ionization region and being irradiated by photons emitted from a vacuum ultraviolet lamp (such as a krypton lamp at 10.0 eV or a xenon lamp at 10.4 eV). If the ionization energy of the sample molecule (M) is lower than the photon energy, direct photoionization occurs.

[0005] M+hν→M ++ +e -

[0006] The ionization process of VOCs under ultraviolet light is actually a typical photophysical and photochemical process, the core of which is "photoionization". This process requires photons with sufficiently high energy (greater than the VOCs that need to be ionized).

[0007] The ionization energies of common VOCs in the atmosphere are shown in Table 1 (data source: NIST Chemistry Database). Table 1: Ionization energies of common VOCs

[0008]

[0009]

[0010] Among them, some isomers such as C4H 10 Although O (diethyl ether vs. n-butanol) and C4H8O2 (dioxane vs. butyric acid) have the same molecular weight, their properties differ significantly, and they also have different ionization energies.

[0011] A quadrupole mass spectrometer is a commonly used mass spectrometer, typically composed of a UV lamp, a quadrupole assembly, and a photomultiplier tube. Currently available UV lamps generally do not offer selectable light intensity. Different intensities of UV light are required by replacing the UV lamp with one of different specifications. This method of intensity selection is complex and reduces the efficiency of the mass spectrometer. Summary of the Invention

[0012] This application addresses the problem that the light intensity of existing quadrupole mass spectrometers is not selectable by providing a quadrupole mass spectrometer with selectable photoionization light intensity, which allows for convenient selection of photoionization light intensity; in addition, it also provides a method for using the mass spectrometer.

[0013] In a first aspect, this application provides a photoionization intensity-selective quadrupole mass spectrometer, comprising a light source cavity, a main cavity, a quadrupole mass analyzer, a photomultiplier tube, a molecular pump, and an intensity-selective component; wherein:

[0014] The light source cavity is connected to the main cavity in sequence. The light source, the beam collimator and the first lens are installed on the side wall of the light source cavity away from the main cavity. The light intensity selection component is installed inside the light source cavity. The beam collimator is used to collimate the light emitted by the light source into parallel light. The first lens is used to isolate the light source from the light source cavity and transmit the parallel light into the light source cavity. The light intensity selection component is used to select the light intensity of the parallel light.

[0015] A second lens is installed on the partition between the light source cavity and the main cavity; the second lens is used to transmit light with selected intensity into the main cavity.

[0016] A molecular pump is installed on the main chamber to evacuate the main chamber into a vacuum. The main chamber includes an ionization chamber and an analysis chamber connected in sequence, and a through hole is opened on the partition wall between the ionization chamber and the analysis chamber.

[0017] The side wall of the ionization chamber is provided with a sample gas inlet for receiving the gas to be detected, which is ionized in the ionization chamber. An ion collimating lens is installed in the ionization chamber to focus the ions formed by ionization, and the focused ions enter the analysis chamber through a through hole.

[0018] The analysis chamber is equipped with a quadrupole mass analyzer and a photomultiplier tube. The quadrupole mass analyzer is used to screen ions with different mass-to-charge ratios and send them to the photomultiplier tube. The photomultiplier tube is used to amplify the ion current signal and send it to the processor for processing. The processor is used to detect the gas to be tested.

[0019] Optionally, the light source is a short-arc xenon lamp, and the photon energy range of the short-arc xenon lamp is 1eV to 12eV.

[0020] Optionally, the first lens is a circular lens made of magnesium fluoride with a cutoff wavelength of 115 nm.

[0021] Optionally, the light intensity selection component includes a grating and a stepper motor, with the grating mounted on a moving part of the stepper motor, which drives the grating to rotate.

[0022] Optionally, the second lens is a square lens.

[0023] Optionally, an exhaust port is also provided on the side wall of the ionization chamber to extract the remaining unionized gas to be detected.

[0024] Optionally, the ion collimating lens includes three independent lenses, with insulating material installed between each pair of lenses to isolate them from each other. After a DC gradient voltage is applied, each lens pushes the ionized ions to focus and move them to the next stage.

[0025] Optionally, the quadrupole mass analyzer includes a quadrupole pre-bar and a quadrupole, and the photomultiplier tube is a dendroelectric photomultiplier tube; the ion collimating lens, the through hole, the quadrupole pre-bar and the quadrupole are centered on the same straight line, and the quadrupole pre-bar and the quadrupole are aligned.

[0026] Optionally, the analysis chamber is provided with an upper cover plate, which is fixed to the analysis chamber by fasteners, and the molecular pump is mounted on the upper cover plate.

[0027] Secondly, this application provides a method for using a photoionization intensity-selective quadrupole mass spectrometer, including:

[0028] Start the molecular pump to evacuate the main chamber into a vacuum;

[0029] The gas to be tested is introduced into the ionization chamber through the sample inlet;

[0030] Turn on the light source and adjust the light intensity selection component so that the light emitted by the light source enters the ionization chamber according to the set light intensity, thus ionizing the gas to be detected.

[0031] Repeatedly adjust the light intensity selection component to allow light with increased intensity to enter the ionization chamber;

[0032] After ionization, the ions are focused by an ion collimating lens and enter the analysis chamber. The quadrupole mass analyzer filters ions with different mass-to-charge ratios and sends them to a photomultiplier tube. The photomultiplier tube amplifies the ion current signal and sends it to the processor for processing. The processor then performs the detection of the gas to be tested.

[0033] This application has the following technical advantages: By using a light intensity selection component to select the light intensity of the beam entering the ionization chamber, this application achieves flexible selection of photoionization light intensity, greatly optimizing the complex operation of light intensity adjustment in traditional photoionization mass spectrometry systems and significantly improving the working efficiency of the mass spectrometry system. Through flexible adjustment of the incident photon energy, a second dimension of information, namely the energy dimension, is provided in mass spectrometry measurements, which can improve working efficiency in isomerization and material sequence measurement. Attached Figure Description

[0034] Figure 1 This is a three-dimensional structural schematic diagram of an optional embodiment of the photoionization intensity selectable quadrupole mass spectrometer in this application;

[0035] Figure 2 for Figure 1 Front sectional view;

[0036] Figure 3 for Figure 1 A three-dimensional structural diagram of the ionization chamber in the image;

[0037] Figure 4 for Figure 1 A three-dimensional structural diagram of the analysis chamber in the center;

[0038] Figure 5 for Figure 1 A three-dimensional structural diagram of the light intensity selection component.

[0039] Figures 1-5 The system includes: a light source 1, a beam collimator 2, a first lens 3, a light source cavity 4, a stepper motor 5, a grating 6, a partition 7, an ion collimating lens 8, a through hole 9, a quadrupole pre-rod 10, a quadrupole 11, a photomultiplier tube 12, a main cavity 13, a top cover 14, a molecular pump 15, a sample gas inlet 16, a gas extraction port 17, a high connector 18, a low connector 19, a quadrupole locking ring 20, and a second lens 21. Detailed Implementation

[0040] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0041] like Figures 1-5 As shown, this application is a photoionization intensity-selective quadrupole mass spectrometer for detecting volatile organic compounds (VOCs).

[0042] The photoionization intensity-selective quadrupole mass spectrometer includes a light source cavity 4, a main cavity 13, a quadrupole mass analyzer, a photomultiplier tube 12, a molecular pump 15, and an intensity-selective component.

[0043] The light source cavity 4 is sequentially connected to the main cavity 13. A light source 1, a beam collimator 2, and a first lens 3 are mounted on the side wall of the light source cavity 4 away from the main cavity 13. The first lens 3 is mounted on the side wall of the light source cavity 4, and the beam collimator 2 is located between the light source 1 and the first lens 3. The beam collimator 2 is used to collimate the light emitted by the light source 1 into parallel light, ensuring the uniformity of the optical path and measurement accuracy. The first lens 3 is used to isolate the light source 1 from the light source cavity 4 and transmit parallel light into the light source cavity 4.

[0044] A light intensity selection component is installed inside the light source cavity 4; the light intensity selection component is used to select the light intensity of parallel light.

[0045] A second lens 21 is installed on the partition 7 between the light source cavity 4 and the main cavity 13; the second lens 21 is used to transmit light with selected intensity into the main cavity 13.

[0046] A molecular pump 15 is installed on the main chamber 13 to evacuate the main chamber 13 into a vacuum. The main chamber 13 includes an ionization chamber and an analysis chamber connected in sequence. A through hole 9 is provided on the partition wall between the ionization chamber and the analysis chamber. Optionally, the through hole 9 is a tapered hole, which is a common type of vacuum connector, and the ionization chamber and the analysis chamber are connected through the tapered hole.

[0047] An inlet gas port 16 is provided on the side wall of the ionization chamber for receiving the gas to be detected, which is then ionized within the ionization chamber. An ion collimating lens 8 is installed within the ionization chamber to focus the ions formed by ionization. The focused ions enter the analysis chamber through a through-hole 9. The ion collimating lens 8 is fixed to the bottom of the ionization chamber of the main cavity 13 via a low connecting seat 19.

[0048] The analysis chamber is equipped with a quadrupole mass analyzer and a photomultiplier tube 12. The quadrupole mass analyzer is used to screen ions with different mass-to-charge ratios and send them to the photomultiplier tube 12. The photomultiplier tube 12 is used to amplify the ion current signal and send it to the processor for processing. The processor is used to detect the gas to be tested.

[0049] This application uses a molecular pump 15 to evacuate the main chamber 13 into a vacuum, generates a point light source through a light source 1, and then passes through a beam collimator 2, a first lens 3, and enters the light source cavity 4. A light intensity selection component directs the light of the desired wavelength through a second lens 21 on a partition 7, acting on the gas to be detected entering the ionization chamber from the sample gas inlet 16. When the light intensity exceeds the ionization energy of the gas molecules, the sample gas molecules are ionized. The ionized ions are focused by an ion collimating lens 8, and then pass through a through-hole 9 into a quadrupole mass analyzer. The quadrupole mass analyzer filters out ions with different mass-to-charge ratios and sends them to a subsequent photomultiplier tube 12. The photomultiplier tube 12 amplifies the ion current signal and sends it to a processor for processing, ultimately achieving the detection of the sample gas. This application achieves flexible selection of photoionization light intensity, greatly optimizing the complex operation of light intensity selection in traditional photoionization mass spectrometry systems and significantly improving the working efficiency of the mass spectrometry system.

[0050] In one embodiment, the light source 1 is a short-arc xenon lamp. The gap between the two electrodes of the short-arc xenon lamp (i.e. the length of the arc) is very short, ranging from a few tenths of a millimeter to a few millimeters. It is precisely because the arc is short that it can be focused into a very bright spot by the optical system. The photon energy range it produces is 1eV to 12eV, which is used to provide a high-brightness, wide-spectral-range continuous radiation light source.

[0051] In one embodiment, the first lens 3 is a circular lens made of magnesium fluoride (MgF2) with a cutoff wavelength of 115 nm, which can reach 10.8 eV; or the selected material is lithium fluoride (LiF), with a cutoff wavelength of about 105 nm, but with poor performance, which can reach 11.8 eV.

[0052] In one embodiment, the light intensity selection component includes a grating 6 and a stepper motor 5. The grating 6 is mounted on a movable part of the stepper motor 5, which drives the grating 6 to rotate, thereby acquiring light of different intensities. The angle between the grating and the light beam allows a specific wavelength to illuminate the sample. The wavelength corresponds to the energy of the photon.

[0053] The principle of using a grating to select light of different wavelengths is as follows:

[0054] When parallel light shines on a grating (diffraction grating), light of different wavelengths is dispersed (dispersed) to different angles. This is the basic principle of using a grating to select light of different wavelengths. The physical process is mainly based on the combined effect of multi-slit interference and single-slit diffraction (commonly known as the diffraction grating equation).

[0055] Core principle: Grating equation

[0056] The grating equation determines the angle at which light of a specific wavelength exhibits its principal maximum (i.e., the brightest interference fringe):

[0057] d(sinθm+sinθi)=mλd(sinθm+sinθi)=mλ

[0058] in:

[0059] d: Grating constant (distance between adjacent gratings)

[0060] i: Angle of incidence (angle between the incident light and the grating normal)

[0061] θm: The m-th order diffraction angle (the angle between the diffracted light and the normal)

[0062] m: Diffraction order (integer, m = 0, ±1, ±2, ...)

[0063] λ: Wavelength of light

[0064] In the common case of normal incidence (θi=0), the formula simplifies to:

[0065] dsinθm=mλdsinθm=mλ

[0066] Methods for selecting different wavelengths of light:

[0067] 1. Dispersion

[0068] According to the grating equation, for fixed d and m, the larger the wavelength λ, the larger the corresponding sinθm, that is, the larger the diffraction angle of long wavelength light.

[0069] Therefore, when a beam of parallel white light passes through a grating, light of different wavelengths will be spatially separated, forming a spectrum (similar to a rainbow).

[0070] 2. Select light of a specific wavelength

[0071] (1) Fix the grating and rotate the detector (or exit slit).

[0072] A slit or fiber optic probe is placed in a specific diffraction angle direction. The grating or detector is rotated so that only light energy with a diffraction angle corresponding to the target wavelength can pass through the slit and enter the subsequent optical system (such as a photodetector or monochromator).

[0073] (2) Fix the detector and rotate the grating.

[0074] By rotating the grating to change the relationship between the incident angle θi and the diffraction angle θm, the target wavelength can be precisely aligned with the fixed exit slit. This is a common method used in monochromators.

[0075] Key parameters and selection factors

[0076] Grating constant d:

[0077] The smaller d is, the greater the dispersion (the larger the angle between adjacent wavelengths), and the higher the resolution may be, but the working order m needs to be selected appropriately.

[0078] Diffraction order m:

[0079] Higher orders (with larger m) exhibit greater dispersion, but their light intensity is usually weaker, and order overlap may occur (different orders of different wavelengths at the same angle).

[0080] Raster type:

[0081] Transmission gratings or reflection gratings, with reflection gratings (such as blazed gratings) concentrating energy to specific orders, are more efficient.

[0082] Resolution:

[0083] The resolution of a grating is R = λΔλ = mNR = Δλλ = mN, where N is the total number of grating lines. The more lines, the higher the resolution.

[0084] Through the dispersive effect of the grating, light of different wavelengths is diffracted in different directions; by rotating the grating or detector, or by placing a slit / detector at a specific position, a single wavelength can be selected or multiple wavelengths can be recorded simultaneously.

[0085] In one embodiment, the second lens 21 is a square lens, which is fixed to the partition 7 to separate the light source cavity 4 from the main cavity 13. The required intensity of light is allowed to pass through the square lens and enter the main cavity 13 by adjusting the angle of the grating 6. The square lens is embedded with MgF2 and LiF to reduce cross-contamination within the cavity.

[0086] In one embodiment, an exhaust port 17 is also provided on the side wall of the ionization chamber, which is used to extract the remaining unionized gas to be detected.

[0087] In one embodiment, the ion collimating lens 8 includes three independent lenses, with insulating material installed between each pair of lenses to isolate them from each other. Each lens, after applying a DC gradient voltage, pushes the ionized ions to focus and move them to the next stage.

[0088] In one embodiment, the quadrupole mass analyzer includes a quadrupole pre-bar 10 and a quadrupole 11, and the photomultiplier tube 12 is a darad photomultiplier tube 12; the quadrupole 11 is fixed by a quadrupole locking ring 20, which is fixed to the bottom of the main cavity 13 by a high-connector 18; the ion collimating lens 8, the through hole 9, the quadrupole pre-bar 10 and the quadrupole 11 are all on the same straight line, and the quadrupole pre-bar 10 and the quadrupole 11 are aligned.

[0089] In one embodiment, an upper cover plate 14 is provided on the analysis chamber and is fixed to the analysis chamber by fasteners. A molecular pump 15 is mounted on the upper cover plate 14. Before the sample gas enters the main chamber 13, the molecular pump 15 is started to evacuate the inside of the chamber.

[0090] This application also provides a method for using a photoionization intensity-selective quadrupole mass spectrometer, including:

[0091] Start the molecular pump 15 to evacuate the main chamber 13 into a vacuum;

[0092] The gas to be tested is introduced into the ionization chamber through the sample gas inlet 16;

[0093] Turn on light source 1 and adjust the light intensity selection component so that the light emitted by light source 1 enters the ionization chamber according to the set light intensity, so that the gas to be detected is ionized.

[0094] Repeatedly adjust the light intensity selection component to allow light with increased intensity to enter the ionization chamber;

[0095] After ionization, the ions are focused by the ion collimating lens 8 and enter the analysis chamber. The quadrupole mass analyzer filters ions with different mass-to-charge ratios and sends them to the photomultiplier tube 12. The photomultiplier tube 12 amplifies the ion current signal and sends it to the processor for processing. The processor then performs the detection of the gas to be detected.

[0096] The data processing method provided in this application is as follows:

[0097] First, adjust the grating angle to allow low-energy photons (hν_1) to be incident, ionize the sample gas, and obtain the spectrum MassSpectrometry_1;

[0098] Then, repeat the previous operation, continuously increasing the photon energy, and obtain the corresponding spectrum MassSpectrometry_i by incident photons with energy hν_i;

[0099] Finally, after completing this process, the obtained N MassSpectrometry (1-N) spectra are differentially processed to further distinguish the different VOCs species.

[0100] This application can ionize different organic components with different photon energies, facilitating the analysis of VOCs composition. By continuously adjusting the photon energy and then using the difference between the data in the spectra, the proportion of different VOCs components can be determined. This application achieves rapid and accurate measurement of VOCs composition by combining a spectral difference algorithm with the ionization energy of common volatile organic compounds (VOCs).

[0101] The foregoing has provided a sufficiently detailed and specific description of this application. Those skilled in the art should understand that the descriptions in the embodiments are merely exemplary, and all changes made without departing from the true spirit and scope of this application should fall within the protection scope of this application. The scope of protection claimed in this application is defined by the claims, and not by the above descriptions in the embodiments.

Claims

1. A photoionization intensity selectable quadrupole mass spectrometer, characterized in that, It includes a light source cavity, a main cavity, a quadrupole mass analyzer, a photomultiplier tube, a molecular pump, and a light intensity selection component; wherein: The light source cavity is sequentially connected to the main cavity. A light source, a beam collimator, and a first lens are installed on the side wall of the light source cavity away from the main cavity. The light intensity selection component is installed inside the light source cavity. The beam collimator is used to collimate the light emitted by the light source into parallel light. The first lens is used to isolate the light source from the light source cavity and transmit the parallel light into the light source cavity. The light intensity selection component is used to select the light intensity of the parallel light. A second lens is installed on the partition between the light source cavity and the main cavity; the second lens is used to allow light with selected intensity to be transmitted into the main cavity. The molecular pump is installed on the main cavity and is used to evacuate the main cavity into a vacuum; the main cavity includes an ionization chamber and an analysis chamber connected in sequence, and a through hole is opened on the partition wall between the ionization chamber and the analysis chamber; The ionization chamber has a sample gas inlet on its side wall for receiving the gas to be detected, which is then ionized within the ionization chamber. An ion collimating lens is installed within the ionization chamber to focus the ionized ions, which then enter the analysis chamber through the through-hole. The analysis chamber is equipped with the quadrupole mass analyzer and the photomultiplier tube; the quadrupole mass analyzer is used to screen ions with different mass-to-charge ratios and send them to the photomultiplier tube, the photomultiplier tube is used to amplify the ion current signal and send it to the processor for processing, and the processor is used to detect the gas to be detected.

2. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The light source is a short-arc xenon lamp, and the photon energy range of the short-arc xenon lamp is 1eV to 12eV.

3. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The first lens is a circular lens, made of magnesium fluoride, with a cutoff wavelength of 115 nm.

4. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The light intensity selection component includes a grating and a stepper motor. The grating is mounted on the movable part of the stepper motor, and the stepper motor is used to drive the grating to rotate.

5. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The second lens is a square lens.

6. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, An exhaust port is also provided on the side wall of the ionization chamber, which is used to extract the remaining unionized gas to be detected.

7. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The ion collimating lens comprises three independent lenses, with insulating material installed between each pair of lenses to isolate them from each other. After a DC gradient voltage is applied, each lens pushes the ionized ions to focus and move them to the next stage.

8. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The quadrupole mass analyzer includes a quadrupole pre-bar and a quadrupole, and the photomultiplier tube is a datum photomultiplier tube; the ion collimating lens, the through hole, the quadrupole pre-bar and the quadrupole are all on the same straight line, and the quadrupole pre-bar is aligned with the quadrupole.

9. The photoionization intensity selectable quadrupole mass spectrometer according to claim 1, characterized in that, The analysis chamber is provided with an upper cover plate, which is fixed to the analysis chamber by fasteners, and the molecular pump is mounted on the upper cover plate.

10. A method of using a photoionization intensity selectable quadrupole mass spectrometer according to claims 1 to 9, characterized in that, The method includes: The molecular pump is activated to evacuate the main chamber into a vacuum. The gas to be detected is introduced into the ionization chamber through the sample inlet port; Turn on the light source and adjust the light intensity selection component so that the light emitted by the light source enters the ionization chamber according to the set light intensity, so that the gas to be detected is ionized; Repeatedly adjust the light intensity selection component to allow light with increased intensity to enter the ionization chamber; After ionization, the ions are focused by the ion collimating lens and enter the analysis chamber. The quadrupole mass analyzer filters ions with different mass-to-charge ratios and sends them to the photomultiplier tube. The photomultiplier tube amplifies the ion current signal and sends it to the processor for processing. The processor then detects the gas to be detected.

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