Large space vocs detection photoionization source

Abstract

The application discloses a large-space VOCs detection photoionization source for mass spectrometry, comprising an ionization source cavity, a sample sampling port, a VUV light source, an array VUV light source fixing electrode, an ion transmission electrode, an ion extraction electrode and a radio frequency power supply system. Since the sensitivity of the mass spectrometry ionization source is closely related to sample utilization, in order to improve the sensitivity of the ionization source, the sample ionization space can be increased. The VUV light source is designed in a large-space array, which on the one hand increases the ionization space, improves the sample utilization, and on the other hand increases the residence time, improves the sample ionization efficiency; in addition, the radio frequency electric field is introduced into the ionization source, and the ions generated in the large ionization space are converged, so that the sensitivity of VOCs detection is finally improved. The application can effectively improve the detection sensitivity of the mass spectrometer to VOCs, and has a wide application prospect in the technical field of VOCs detection in atmospheric environment, industrial process, medical diagnosis and the like.

Description

Technical Field

[0001] This invention relates to the field of mass spectrometry analysis technology, and in particular to a photoionization source for detecting VOCs in a large space for mass spectrometry analysis. Background Technology

[0002] Volatile organic compounds (VOCs) are not only important precursors to PM2.5 and ozone, but most are also biotoxic, posing a threat to human health. However, environmental VOCs are characterized by their wide distribution, diverse types, low concentrations, and rapid spatiotemporal variations, posing new challenges to VOCs monitoring technologies and necessitating the development of ultra-sensitive and rapid monitoring technologies. Ionization sources are the core of mobile mass spectrometry (WMS), influencing the sensitivity of the mass spectrometer, the types of detectable compounds, and ion characteristics. In recent years, soft ionization technology has effectively solved the peak overlap problem caused by the high fragmentation of traditional electron impact ionization (EI) technology, resulting in simple and easily interpretable spectra, making it highly suitable for environmental VOCs monitoring. Soft ionization sources mainly include proton transfer reaction (PTR) ionization sources and vacuum ultraviolet photoionization sources (VUV-PI). Among them, VUV lamp-based PI ionization sources have advantages such as compact structure and low power consumption, and have been widely used in environmental monitoring mass spectrometry. The ionization efficiency of a PI ionization source is closely related to light intensity, molecular number density, optical path length, and ionization space. While numerous studies have reported improving PI source sensitivity by increasing light intensity and molecular number density, reports on improving sensitivity through optical path length and ionization space are relatively few. This is mainly because while increasing optical path length and ionization space increases the number of ions generated, the large ion space also poses challenges for ion collection. Furthermore, VOCs generally have large sample sizes, while current mass spectrometry ionization sources are primarily used for laboratory analysis with relatively small injection flow rates and ionization spaces, making it difficult to effectively utilize large VOC samples. Therefore, the design of large-space array ionization sources could be developed to match VOC detection.

[0003] Through patent and paper searches, the following patents related to mass spectrometer ionization source signal correction were found: 1. A patent application filed and disclosed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences on December 17, 2012, regarding an array-type photoelectric emission ionization source and its application. This technology is used for ion mobility spectrometry. The array-type photoelectric emission ionization source significantly increases light intensity, greatly increasing the number of ions ionized in the ionization region and effectively improving the sensitivity of the ion mobility tube. On the one hand, the ionization source design is specifically for ion mobility spectrometry; on the other hand, this method has very low ion collection efficiency under atmospheric pressure conditions. 2. A patent application filed and disclosed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences on November 21, 2013, regarding an ionization source based on vacuum ultraviolet light nanoarray modification to enhance photoelectron emission. This invention modifies the electrode surface with a nano-gold array, utilizing the surface plasmon resonance effect of the nano-gold array to improve the efficiency of photoelectrons generated by the vacuum ultraviolet lamp, enhancing sensitivity and improving the stability of the ionization source without changing the ultraviolet light intensity. This invention is mainly used for photoelectron or photoelectron-induced ionization and is ineffective for single-photon ionization. In summary, there are currently no patent reports on large-space ionization and effective ion collection technologies. Summary of the Invention

[0004] This invention proposes a large-space VOCs detection photoionization source for mass spectrometers to further improve the sensitivity of VOCs detection by mass spectrometry.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] 1. A photoionization source for large-space VOCs detection, comprising a sample sampling port, an ionization source cavity, a VUV light source, an array of VUV light source fixed electrodes, an ion transport electrode, an ion extraction electrode, and a radio frequency power supply system, characterized in that:

[0007] The X direction is to the right, and the Y direction is upward.

[0008] The ionization source cavity is a hollow closed cylindrical chamber, and a sample sampling port is arranged on the left side wall of the ionization source cavity. The center of the circular sample sampling port is coaxially arranged with the center of the ionization source cavity. Three or more groups of array VUV light source fixed electrodes and ion transmission electrode combination structures are sequentially arranged in the ionization source cavity along the X direction from left to right. Each group of combination structure is composed of an array VUV light source fixed electrode and an ion transmission electrode. An ion extraction electrode is arranged at the end (i.e. the right end) of the ionization source cavity. The middle through hole of the ion extraction electrode is in communication with the outside of the ionization source cavity. The array VUV light source fixed electrode, the ion transmission electrode and the ion extraction electrode are all flat plate structures with through holes in the middle. They are all placed in parallel, coaxial and spaced apart. Four cylindrical through holes are symmetrically arranged on the array VUV light source fixed electrode along the radial direction (perpendicular to the X direction) as light windows. The axes of adjacent light windows are perpendicular to each other. A VUV light source is arranged outside the light window away from the VUV light source fixed electrode. The light emitted by the VUV light source enters the middle through hole of the array VUV light source fixed electrode through the light window. The VUV light source is placed outside the array VUV light source fixed electrode, and the axis of the light outlet of the VUV light source is coaxially placed with the axis of the light window, and is perpendicular to the axis of the ionization source cavity. The array VUV light source fixed electrode is connected to the RF+ port of the radio frequency power supply system through a capacitor with a capacity of C. The ion transmission electrode is connected to the RF- port of the radio frequency power supply system through a capacitor with a capacity of C. Along the X direction, the array VUV light source fixed electrode and the adjacent ion transmission electrode are sequentially connected in order through resistors Ri (i is an integer from 1 to i, i>5). The resistance value of the resistor Ri increases in proportion or linearly with the value i.

[0009] Further, the sample sampling port can be one or more of a metal capillary, a PEEK capillary or a quartz capillary. The length is 0.05-5m, and the inner diameter is 25-500μm.

[0010] Further, the diameter of the middle through hole of the array VUV light source fixed electrode is 2-20mm. The diameter of the middle through hole of the ion transmission electrode is 2-20mm. The diameter of the middle through hole of the ion extraction electrode is 0.2-5mm.

[0011] Further, along the X direction, different voltages V1, V2 are sequentially loaded on the first array VUV light source fixed electrode and the last ion transmission electrode in order from high to low voltage under the voltage division of the resistor Ri, and an ion transmission non-uniform electric field with a size of 1-100V / cm is formed. The resistance value of the resistor Ri is 1KΩ-100MΩ.

[0012] Further, the radio frequency power supply system outputs a radio frequency amplitude of 10-1000V and a frequency of 0.5-5MHz.

[0013] Further, the ion extraction electrode is connected with a mass analyzer, and the mass analyzer is a time-of-flight mass analyzer, a quadrupole mass analyzer or an ion trap mass analyzer.

[0014] Further, the VUV light source is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source.

[0015] The internal gas pressure of the ion source cavity is 1-1000 Pa.

[0016] The present application designs a large space array for the VUV light source, which increases the ionization space and improves the sample utilization rate, and increases the residence time and improves the sample ionization efficiency; in addition, the radio frequency electric field is introduced into the ion source to converge the ions generated in the large ionization space, and finally the purpose of improving the sensitivity of VOCs detection is achieved. The present application can effectively improve the detection sensitivity of VOCs by mass spectrometer, and has wide application prospect in the VOCs detection technology field of atmospheric environment, industrial process, medical diagnosis and the like. BRIEF DESCRIPTION OF DRAWINGS

[0017] The drawings further illustrate the present application, but the contents of the drawings do not constitute any limitation on the present application.

[0018] Figure 1 is a schematic diagram of the overall structure of a large space VOCs detection photoionization source according to one embodiment of the present application; 1 is sample gas. DETAILED DESCRIPTION

[0019] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0020] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme of the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, but not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0021] It is to be understood that the terms so far as the language goes used in this patent are only used to describe specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, devices, components and / or combinations thereof, but do not preclude the presence or addition of one or more other features, steps, operations, devices, components, and / or combinations thereof.

[0022] The relative arrangement of parts and steps, numerical expressions, and numerical values set forth in the examples are not intended to limit the scope of the present application unless otherwise specifically stated. It is to be understood that the actual dimensions of the various parts shown in the drawings are not necessarily to scale as the dimensions are shown by way of illustration only. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art can not be discussed in detail, but should be considered as if the discussion were fully conveyed. In all examples shown and discussed herein, any specific numerical value should be interpreted as merely an example, and not a limitation. Other examples of the exemplary embodiments can have different values. It should be noted that like reference numerals and letters refer to like items in the following drawings, and once an item is defined in one drawing, it need not be discussed further in subsequent drawings.

[0023] In the description of the present application, it should be noted that the orientation words such as "front, back, up, down, left, right", "horizontal, vertical, perpendicular, horizontal", and "top, bottom" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate and imply that the indicated device or element must have a specific orientation or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the scope of protection of the present application: the orientation words "inner, outer" refer to the inner and outer relative to the contour of the parts themselves.

[0024] The large-space VOCs detection photoionization source for mass spectrometers of the present embodiment comprises a sample sampling port 2, an ionization source cavity 5, a VUV light source 3, an array VUV light source fixed electrode 6, an ion transmission electrode 7, an ion extraction electrode 8, and an RF power supply system 9, characterized in that:

[0025] The right direction is the X direction, and the upward direction is the Y direction.

[0026] The ionization source cavity 5 is a hollow closed cylindrical chamber, and a sample sampling port 2 is arranged on the left side wall of the ionization source cavity 5. The center of the circular sample sampling port is coaxially arranged with the center of the ionization source cavity 5. Inside the ionization source cavity 5, three groups of array VUV light source fixed electrodes 6 and ion transmission electrodes 7 are sequentially arranged along the X direction from left to right. Each group of combination is composed of an array VUV light source fixed electrode 6 and an ion transmission electrode 7. An ion extraction electrode 8 is arranged at the end (i.e. the right end) of the ionization source cavity 5. The middle through hole of the ion extraction electrode 8 is connected with the outside of the ionization source cavity 5. The array VUV light source fixed electrode 6, the ion transmission electrode 7 and the ion extraction electrode 8 are all flat plate structures with through holes in the middle. They are all parallel, coaxial and spaced apart. Four cylindrical through holes are symmetrically arranged on the array VUV light source fixed electrode 6 along the radial direction (perpendicular to the X direction) as light windows 4. The axes of adjacent light windows 4 are perpendicular to each other. A VUV light source 3 is arranged outside the light window 4 away from the VUV light source fixed electrode. The light emitted by the VUV light source 3 enters the middle through hole of the array VUV light source fixed electrode 6 through the light window 4. The VUV light source 3 is placed outside the array VUV light source fixed electrode 6, and the axis of the light outlet of the VUV light source 3 is coaxially arranged with the axis of the light window 4, and is perpendicular to the axis of the ionization source cavity 5. The array VUV light source fixed electrode 6 is connected with the RF+ port of the radio frequency power supply system 9 through a capacitor with a capacity of C. The ion transmission electrode 7 is connected with the RF- port of the radio frequency power supply system 9 through a capacitor with a capacity of C. Along the X direction, the array VUV light source fixed electrode 6 and the adjacent ion transmission electrode 7 are sequentially connected through resistors Ri (i is an integer from 1 to i, i>5) in order. The resistance value of the resistor Ri increases proportionally or linearly with the value i.

[0027] Further, the sample sampling port 2 can be one or more of a metal capillary, a PEEK capillary or a quartz capillary. The length is 0.05-5m, and the inner diameter is 25-500μm.

[0028] Preferably, the sample 1 sampling port 2 selects a passivated metal capillary. The length is 0.5m, and the inner diameter is 250μm.

[0029] Further, the diameter of the middle through hole of the array VUV light source fixed electrode 6 is 2-20mm. The diameter of the middle through hole of the ion transmission electrode 7 is 2-20mm. The diameter of the middle through hole of the ion extraction electrode 8 is 0.2-5mm.

[0030] Preferably, the diameter of the center hole of the array VUV light source fixed electrode 6 is 10mm. The diameter of the center hole of the ion transmission electrode 7 is 10mm. The diameter of the center hole of the ion extraction electrode 8 is 1mm.

[0031] Further, along the X direction, the first array of VUV light source fixed electrode 6 and the last ion transmission electrode 7 are loaded with different voltages V1, V2 in the order of high to low voltage, and the ion transmission non-uniform electric field with a size of 1-100 V / cm is formed under the voltage division of resistor Ri; the resistance of resistor Ri is 1KΩ-100MΩ.

[0032] Preferably, along the X direction, the first array of VUV light source fixed electrode 6 and the last ion transmission electrode 7 are loaded with different voltages 50V and 15V in the order of high to low voltage, and the ion extraction electrode 8 is applied with a voltage of 10V to match the rear-end mass spectrometry system; the resistance of resistor Ri is 1, 2, 3, 4…MΩ.

[0033] Further, the radio frequency power supply system 9 outputs a radio frequency amplitude of 10-1000V and a frequency of 0.5-5MHz.

[0034] Preferably, the radio frequency power supply system 9 outputs a radio frequency amplitude of 200V and a frequency of 2MHz.

[0035] Further, the ion extraction electrode 8 is connected with a mass analyzer, which is a time-of-flight mass analyzer, a quadrupole mass analyzer or an ion trap mass analyzer.

[0036] Further, the VUV light source 3 is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source; the internal gas pressure of the ion source cavity 5 is 1-1000Pa.

[0037] Preferably, the internal gas pressure of the ion source cavity 5 is 500Pa.

[0038] The technical principles of the present application are described above in combination with specific embodiments. These descriptions are only for explaining the principles of the present application, and cannot be interpreted as limiting the scope of protection of the present application in any way. Based on the explanations herein, other specific embodiments of the present application can be conceived by those skilled in the art without creative efforts, and these equivalent variations or replacements are all included in the scope defined by the claims of the present application.

[0039] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A photoionization source for detecting VOCs in a large space, comprising a sample sampling port (2), an ionization source cavity (5), a VUV light source (3), an array of VUV light source fixed electrodes (6), an ion transport electrode (7), an ion extraction electrode (8), and a radio frequency power supply system (9), characterized in that: The X direction is to the right, and the Y direction is upward. The ionization source cavity (5) is a hollow, sealed cylindrical chamber. A sample sampling port (2) is provided on the left side wall of the ionization source cavity (5). The center of the circular sample sampling port (2) is coaxially arranged with the center of the ionization source cavity (5). Inside the ionization source cavity (5), from left to right along the X direction, there are three or more sets of array VUV light source fixed electrodes (6) and ion transport electrodes (7) in combination. Each combination consists of array VUV light source fixed electrodes (6) and ion transport electrodes (7). An ion extraction electrode (8) is provided at the end (right end) of the ionization source cavity (5); the through hole in the middle of the ion extraction electrode (8) is connected to the outside of the ionization source cavity (5); the array VUV light source fixed electrode (6), ion transport electrode (7), and ion extraction electrode (8) are all flat plate structures with through holes in the middle, and they are all parallel, with the through holes in the middle coaxial and spaced apart; four cylindrical through holes are symmetrically arranged along the radial direction (perpendicular to the X direction) on the array VUV light source fixed electrode (6) as... The optical windows (4) are arranged with their axes perpendicular to each other. A VUV light source (3) is provided on the outside of the optical window (4) away from the VUV light source fixed electrode. The light emitted by the VUV light source (3) enters the through hole in the middle of the array VUV light source fixed electrode (6) through the optical window (4). The VUV light source (3) is placed outside the array VUV light source fixed electrode (6), and the light outlet axis of the VUV light source (3) is placed coaxially with the axis of the optical window (4) and perpendicular to the axis of the ionization source cavity (5). The array VUV light source fixed electrode (6) is connected to the RF+ port of the radio frequency power supply system (9) through a capacitor with a capacitance of C. The ion transport electrode (7) is connected to the RF- port of the radio frequency power supply system (9) through a capacitor with a capacitance of C. Along the X direction, the array VUV light source fixed electrode (6) and the adjacent ion transport electrode (7) are connected sequentially through resistors Ri (i is an integer from i to i, i>5). The resistance value of the resistor Ri increases proportionally or linearly with the value of i.

2. The photoionization source according to claim 1, characterized in that: The sample sampling port (2) can be one or more of the following: metal capillary, PEEK capillary or quartz capillary; the length is 0.05 to 5 m and the inner diameter is 25 to 500 μm.

3. The photoionization source according to claim 1, characterized in that: The diameter of the through hole in the middle of the fixed electrode (6) of the array VUV light source is 2-20 mm; the diameter of the through hole in the middle of the ion transport electrode (7) is 2-20 mm; and the diameter of the through hole in the middle of the ion extraction electrode (8) is 0.2-5 mm.

4. The photoionization source according to claim 1, characterized in that: Along the X direction, different voltages V1 and V2 are applied sequentially on the first array VUV light source fixed electrode (6) and the last ion transport electrode (7) in order from high to low voltage, and a non-uniform electric field for ion transport with a magnitude of 1 to 100 V / cm is formed under the voltage division of resistor Ri; the resistance of resistor Ri is 1 KΩ to 100 MΩ.

5. The photoionization source according to claim 1, characterized in that: The radio frequency power supply system (9) outputs a radio frequency amplitude of 10 to 1000V and a frequency of 0.5 to 5MHz.

6. The photoionization source according to claim 1, characterized in that: The ion extraction electrode (8) is connected to a mass analyzer, which is a time-of-flight mass analyzer, a quadrupole mass analyzer, or an ion trap mass analyzer.

7. The photoionization source according to claim 1, characterized in that: The VUV light source (3) is a gas discharge lamp light source, a laser light source or a synchrotron radiation light source; the internal gas pressure of the ionization source cavity (5) is 1 to 1000 Pa.

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