A multi-mode ion source and a mode switching method thereof

Abstract

The multi-mode ion source comprises a filament assembly, a lens assembly and a transmission assembly arranged in sequence along an ion extraction direction, the lens assembly comprises at least one adjustable lens, the size of the lens hole in the middle of the adjustable lens is adjustable, the ion channel can be formed, and the gas pressure of the collision chamber can be adjusted, so that the multi-mode ion source has an EI mode, a CI mode and a transition mode between the EI mode and the CI mode, and the integration of multiple modes is realized; the mode switching method of the multi-mode ion source adopts the above multi-mode ion source, when it is needed to switch the multi-mode ion source to the EI mode, the reaction gas is closed first, and then the lens hole of the adjustable lens is expanded to reduce the gas pressure of the collision chamber; when it is needed to switch the multi-mode ion source to the CI mode, the lens hole of the adjustable lens is first reduced, and then the reaction gas is introduced to increase the gas pressure of the collision chamber, and the method is simple to operate and easy to implement.

Description

Technical Field

[0001] This invention belongs to the field of analytical instrument technology, specifically relating to a multi-mode ion source and its mode switching method. Background Technology

[0002] In mass spectrometry, the ion source is the core component used to convert neutral sample molecules into gaseous ions. Its performance directly affects the sensitivity, selectivity, and range of analyzable compounds of the mass spectrometer. In the field of gas chromatography-mass spectrometry (GC-MS), electron ionization (EI) and chemical ionization (CI) are the two most widely used classical ionization techniques.

[0003] The working principle of an electron ionization (EI) source is as follows: high-energy electrons (typically 70 eV) emitted by a heated filament directly bombard gaseous sample molecules under vacuum conditions, causing the sample molecules to lose an electron and form positively charged molecular ions (M). + •), and then the molecular ion undergoes chemical bond breakage, producing a series of characteristic fragment ions.

[0004] The main advantages of EI are: abundant fragment ions, providing detailed molecular structure information; good spectral reproducibility, with a large standard mass spectrometry library (such as the NIST mass library and the Wiley mass library), allowing users to quickly identify unknown substances through library searches; and relatively simple hardware structure with good long-term stability.

[0005] However, EI has significant technical limitations: for thermally unstable, low-volatility, or easily degradable compounds, the high energy input of 70 eV often results in the molecular ion peak being too weak or even disappearing completely, making it impossible to accurately determine the molecular weight of the compound; for highly polar compounds (such as alcohols, carboxylic acids, glycosides, etc.), it is usually difficult to observe the molecular ion peak in EI spectra, thus losing crucial structural information.

[0006] To compensate for the shortcomings of electroionization (EI) in determining molecular weight, chemical ionization (CI) sources were proposed. The working principle of CI is as follows: first, reactive plasma is generated by bombarding reactive gases (such as methane, isobutane, ammonia, etc.) with electrons; then, sample molecules undergo proton transfer, charge exchange, or addition reactions with ions in the plasma to generate quasi-molecular ions (such as [M+H)). + [M+NH4] + The product ions are mainly composed of ions.

[0007] The main advantages of CI are: fewer fragment ions, prominent quasi-molecular ion peaks, making it easy to accurately determine molecular weight; ionization selectivity can be adjusted by selecting different reaction gases (based on differences in proton affinity); it is relatively mild for thermally unstable compounds and is suitable for substances that are difficult to analyze under EI.

[0008] However, CI also has significant limitations: poor spectral reproducibility, with large differences in mass spectra obtained under different types of reactant gases and different reaction gas pressures, making it difficult to establish a universal standard mass spectrometry library; insufficient structural information, lack of characteristic fragment ions, making it difficult to infer functional groups and molecular skeletons; the need to introduce reactant gases, increasing hardware complexity and maintenance costs, and requiring high purity of reactant gases; and ionization efficiency is significantly affected by parameters such as sample volatility, reaction gas pressure, and ion source temperature, making method development quite cumbersome.

[0009] Furthermore, since CI requires collisions with reactant gases, the gas pressure is often higher than that of EI. Switching between EI and CI inevitably involves gas pressure adjustment. However, most lenses of ion sources have holes for ions to pass through. The size of these holes is fixed and cannot adjust the gas pressure in the collision chamber. Therefore, CI and EI cannot be integrated into the same ion source, making it difficult to study the transition state between EI and CI. Summary of the Invention

[0010] The purpose of this invention is to overcome one or more shortcomings in the prior art and provide a multi-mode ion source and a mode switching method thereof.

[0011] To achieve the above objectives, the product in the technical solution adopted by the present invention is a multi-mode ion source, comprising a filament assembly, a lens assembly, and a transmission assembly arranged sequentially along the ion extraction direction. The lens assembly is characterized in that: the lens assembly includes at least one adjustable lens, the size of the lens aperture in the middle of the adjustable lens is adjustable, and the lens aperture can both form an ion channel and adjust the gas pressure in the collision chamber, enabling the multi-mode ion source to have an EI mode, a CI mode, and a transition mode between the EI and CI modes.

[0012] Preferably, the adjustable lens includes two coaxially spaced annular plates and a plurality of sliding plates disposed between the two annular plates. The inner walls of the two annular plates are located on the same columnar virtual surface. The sliding plates have a tip extending into the virtual surface and a tail clamped between the two annular plates. All the sliding plates are evenly distributed around the axis of the virtual surface and the sidewalls of adjacent sliding plates slide against each other, so that all the tips surround the lens aperture on the inner side of the virtual surface. One of the two annular plates can rotate relative to the other around the axis of the virtual surface. When it rotates, it can drive all the sliding plates to move synchronously, causing the lens aperture to expand or shrink. When it stops rotating, it can keep the lens aperture in its current state.

[0013] More preferably, the surfaces of the two annular plates facing each other are provided with guide grooves, and the two sides of the tail are provided with protrusions that match the guide grooves and are inserted into the guide grooves. When the two annular plates rotate relative to each other, the protrusions can be forced to move through the guide grooves, thereby driving the slide plate to move to enlarge or shrink the lens hole.

[0014] More preferably, the guide groove on one of the annular plates is a long straight groove, the guide groove on the other annular plate is an arc-shaped groove, and the protrusion on the tail that matches the long straight groove is a strip-shaped protrusion and the protrusion that matches the arc-shaped groove is a columnar protrusion.

[0015] More preferably, the long straight groove extends tangentially along the inner hole of the annular plate in which it is located, the strip-shaped protrusion is slidably inserted into the long straight groove, the arc-shaped groove penetrates the annular plate in the thickness direction, and the columnar protrusion is slidably and rotatably inserted into the arc-shaped groove.

[0016] More preferably, one of the annular plates has an outwardly extending push rod on its outer circumferential surface, the push rod being used to drive the annular plate to rotate relative to the other annular plate.

[0017] More preferably, the multi-mode ion source further includes a drive assembly for driving the push rod, the drive assembly including a motor.

[0018] More preferably, the two side walls of the tip are flat surfaces, and the hole is a regular polygonal hole.

[0019] More preferably, both the annular plate and the sliding plate are conductive metal plates.

[0020] Preferably, the filament assembly includes an inner filament cover, an outer filament shield, and a filament disposed between the filament cover and the filament shield; the transmission assembly includes a quadrupole transmission assembly and an octupole transmission assembly.

[0021] Preferably, the lens assembly further includes a conventional lens, and the adjustable lens is the one closest to the filament assembly in the lens assembly.

[0022] To achieve the above objectives, the method in the technical solution adopted by the present invention is a mode switching method for a multi-mode ion source. The multi-mode ion source is the aforementioned multi-mode ion source. When it is necessary to switch the multi-mode ion source to EI mode, the reaction gas is first turned off and then the lens aperture is enlarged to reduce the gas pressure in the collision chamber. When it is necessary to switch the multi-mode ion source to CI mode, the lens aperture is first narrowed and then the reaction gas is introduced to increase the gas pressure in the collision chamber.

[0023] Preferably, when it is necessary to switch the multi-mode ion source to a transition mode, the lens aperture is gradually reduced from its maximum size, and reaction gas is gradually introduced during this process. When a clean spectrum with satisfactory resolution and repeatability is found, the size of the lens aperture is maintained at its current state, and the gas pressure of the reaction gas is stabilized.

[0024] Preferably, the expansion and contraction of the lens aperture is electrically adjustable, and the electric adjustment can be stopped at any time during the expansion or contraction of the lens aperture to maintain the size of the lens aperture in its current state.

[0025] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art: The multi-mode ion source provided by this invention includes a filament assembly, a lens assembly, and a transmission assembly arranged sequentially along the ion extraction direction. By ensuring that the lens assembly includes at least one adjustable lens, the size of the lens aperture in the middle of the adjustable lens is adjustable. This allows for the formation of an ion channel through the lens aperture, and also enables adjustment of the gas pressure in the collision chamber by adjusting the size of the lens aperture. Thus, the multi-mode ion source has EI mode, CI mode, and a transitional mode between EI and CI modes, achieving multi-mode integration. The mode switching method of the multi-mode ion source provided by this invention, using the above-mentioned multi-mode ion source, requires switching the multi-mode ion source to EI mode by first shutting off the reactive gas and then enlarging the lens aperture of the adjustable lens to reduce the gas pressure in the collision chamber. Conversely, it requires switching the multi-mode ion source to CI mode by first narrowing the lens aperture of the adjustable lens and then introducing reactive gas to increase the gas pressure in the collision chamber. This method requires no disassembly or alignment work, making it simple to operate and easy to implement. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a preferred embodiment of the multimode ion source in this invention.

[0027] Figure 2 yes Figure 1 A three-dimensional schematic diagram of an adjustable lens.

[0028] Figure 3 yes Figure 2 A schematic diagram of the assembly and disassembly.

[0029] Figure 4 yes Figure 2 A front view diagram when the aperture of the central lens is enlarged to its maximum.

[0030] Figure 5 yes Figure 2 A front view diagram with the lens aperture reduced to its smallest size.

[0031] Figure 6 The size of the lens aperture is between Figure 4 and Figure 5 A diagram showing the relationship between them.

[0032] Figure 7 yes Figure 6 Perspective line drawing with the skateboard hidden.

[0033] Figure 8 yes Figure 6 A schematic diagram with the first annular plate hidden.

[0034] Figure 9 yes Figure 8 Cross-sectional view along the AA direction.

[0035] Figure 10 yes Figure 3 A 3D diagram of a single skateboard.

[0036] Figure 11 This is the mass spectrum of benzophenone in EI positive ion mode.

[0037] Figure 12 This is the mass spectrum of benzophenone in CI positive ion mode.

[0038] Figure 13 This is the mass spectrum of benzophenone in the transition state mode between EI positive ion mode and CI positive ion mode.

[0039] Among them: 1. Adjustable lens; 2. Filament cover; 3. Filament shield; 4. Filament; 5. Ordinary lens; 10. First annular plate; 11. Arc groove; 12. Push rod; 20. Second annular plate; 21. Long straight groove; 30. Slide plate; 31. Tip; 32. Tail; 33. Columnar protrusion; 34. Strip protrusion; 40. Lens hole. Detailed Implementation

[0040] like Figures 1 to 10 As shown, the multi-mode ion source provided by the present invention includes a filament assembly, a lens assembly, and a transmission assembly (not shown in the figure) arranged sequentially along the ion extraction direction. The filament assembly includes an inner filament cover 2, an outer filament shield 3, and a filament 4 disposed between the filament cover 2 and the filament shield 3. The transmission assembly includes a quadrupole transmission assembly and an octupole transmission assembly. The lens assembly includes an adjustable lens 1 and two ordinary lenses 5. The adjustable lens 1 is disposed close to the filament assembly, and the size of the lens aperture 40 in the middle of the adjustable lens 1 is adjustable. This lens aperture can both form an ion channel and adjust the gas pressure in the collision chamber, so that the multi-mode ion source has an EI mode, a CI mode, and a transition mode between the EI mode and the CI mode.

[0041] The advantage of this setup is that it can form an ion channel through the lens aperture 40, and the gas pressure in the collision chamber can be adjusted by changing the size of the lens aperture 40, enabling the multi-mode ion source to switch between EI mode, CI mode, and transition mode, thus achieving multi-mode integration. Of course, this multi-mode ion source must have the necessary components of a traditional EI ion source and a CI ion source. These components can be set with reference to existing technologies and will not be described in detail here.

[0042] To achieve adjustment of the size of the lens aperture 40, in this embodiment, the adjustable lens 1 includes: a first annular plate 10, a second annular plate 20, and sliding plates 30. The first annular plate 10 and the second annular plate 20 are coaxially spaced apart, and their inner diameters are equal. The inner walls of the first annular plate 10 and the second annular plate 20 are located on the same columnar virtual surface. Twelve sliding plates 30 are arranged between the first annular plate 10 and the second annular plate 20. Each sliding plate 30 has a pointed portion 31 extending into the virtual surface and a tail portion clamped between the first annular plate 10 and the second annular plate 20. Part 32, twelve slide plates 30 are evenly distributed around the axis of the virtual surface and the side walls of adjacent slide plates 30 slide against each other, so that the tips 31 of all slide plates 30 surround the lens hole 40 of the adjustable lens 1 on the inner side of the virtual surface; the first annular plate 10 is a rotating plate and the second annular plate 20 is a base plate (fixed plate). The first annular plate 10 can rotate relative to the second annular plate 20 around the axis of the virtual surface. When the first annular plate 10 rotates, it can drive all slide plates 30 to move synchronously, so that the lens hole 40 is enlarged or reduced. When the first annular plate 10 stops rotating, it can keep the lens hole 40 in its current state.

[0043] To achieve synchronous movement of all slide plates 30 when the first annular plate 10 rotates, the surface of the first annular plate 10 facing the second annular plate 20 is further provided with an arc-shaped groove 11, which is a through groove penetrating the first annular plate 10 along the thickness direction. The surface of the second annular plate 20 facing the first annular plate 10 is provided with a long straight groove 21, which is a blind groove and extends along the tangent direction of the inner hole on the second annular plate 20. There are twelve arc-shaped grooves 11 and twelve long straight grooves 21, which are evenly distributed around the axis of the virtual surface, together forming a guide groove for the movement of the slide plates 30. The tail 32 of the slide plate 30 facing the side of the first annular plate 10 is provided with a columnar protrusion 33 that matches the arc-shaped groove 11. The columnar protrusion 33 is slidably and rotatably inserted into the arc-shaped groove 11. The side of part 32 facing the second annular plate 20 is provided with a strip-shaped protrusion 34 that matches the long straight groove 21. The strip-shaped protrusion 34 is slidably inserted into the long straight groove 21. In the thickness direction, the long straight groove 21 corresponding to the same slide plate 30 coincides with the arc groove 11 to form a cross shape. When the first annular plate 10 rotates relative to the second annular plate 20, the arc groove 11 can force the columnar protrusion 33 to move. Through the cooperation between the strip-shaped protrusion 34 and the long straight groove 21, as well as the sliding contact of adjacent slide plates 30, all slide plates 30 are driven to slide synchronously, thereby enlarging or shrinking the lens hole 40. The length, angle, and positional relationship of the arc groove 11 and the long straight groove 21 can be flexibly adjusted according to the degree to which the lens hole 40 needs to be enlarged or reduced when the first annular plate 10 rotates by a unit angle. This is not limited here.

[0044] To facilitate the rotation of the first annular plate 10, in this embodiment, the outer circumferential surface of the first annular plate 10 has an outwardly extending push rod 12. The push rod 12 is used to drive the first annular plate 10 to rotate relative to the second annular plate 20. The multimode ion source also includes a driving assembly (not shown in the figure) for driving the push rod 12. The driving assembly includes a motor, and the push rod 12 is a motor push rod 12 matched with the motor. By using a motor to drive the push rod 12, the rotation angle and stopping position of the first annular plate 10 can be precisely controlled. The motor drives the push rod 12 to make the first annular plate 10 rotate and stop relative to the second annular plate 20, so that the multimode ion source has EI mode, CI mode, and a transition mode between EI mode and CI mode.

[0045] To accommodate EI mode, CI mode, and the transition mode between EI mode and CI mode, in this embodiment, the first annular plate 10, the second annular plate 20, and the slide plate 30 are all conductive metal plates. Furthermore, the two side walls of the tip 31 of the slide plate 30 are flat surfaces, so that the lens hole 40 is a regular dodecagonal hole that cannot be completely closed.

[0046] This invention also provides a mode switching method for a multi-mode ion source. When it is necessary to switch the multi-mode ion source to EI mode, the reaction gas is first turned off and then the lens aperture 40 of the adjustable lens 1 is enlarged by motor control. When it is necessary to switch the multi-mode ion source to CI mode, the lens aperture 40 of the adjustable lens 1 is first reduced by motor control and then the reaction gas is introduced. By controlling the size of the lens aperture 40 of the adjustable lens 1, the influence of different collision efficiencies of ions under different gas pressures on the signal peak can be realized, thereby finding a cleaner spectrum with higher resolution and better repeatability. The process of adjusting the size of the lens aperture 40 can also be used to study the transition state between EI and CI. Specifically, when it is necessary to switch the multi-mode ion source to the transition mode, the lens aperture 40 is gradually reduced from its maximum size, and the reaction gas is gradually introduced during this process. When a clean spectrum with the required resolution and repeatability is found, the size of the lens aperture 40 is maintained at the current state, and the gas pressure of the reaction gas is stabilized. This method does not require disassembly or alignment, is simple to operate, easy to implement, and can effectively realize the study of the transition mode between EI and CI modes.

[0047] The following explanation uses the mass spectra of benzophenone in EI positive ion mode, CI positive ion mode, and the transition state mode of both as examples. Figure 11 As shown, when in EI positive ion mode, the aperture of the adjustable lens 1, lens aperture 40, is at its maximum value of 5mm and no reactive gas enters, resulting in multiple fragment ion peaks such as 51 and 77; Figure 12 As shown, when in CI positive ion mode, with the aperture of the adjustable lens 1 (lens aperture 40) at its minimum value of 1 mm and a reaction gas of 5 psi introduced, a molecular ion peak of 183 appears, while fragment ion peaks of 51 and 77 are absent; as Figure 13 As shown, in the transitional mode between the two, the aperture of the adjustable lens 1 lens hole 40 is 2 mm and 1 psi of reaction gas is introduced, resulting in a molecular ion peak of 183 and a fragment ion peak of 52.

[0048] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A multi-mode ion source, comprising a filament assembly, a lens assembly, and a transmission assembly arranged sequentially along the ion extraction direction, characterized in that: The lens assembly includes at least one adjustable lens, the size of which is adjustable. This lens aperture can form an ion channel and adjust the gas pressure in the collision chamber, so that the multi-mode ion source has an EI mode, a CI mode, and a transition mode between the EI and CI modes.

2. The multi-mode ion source according to claim 1, characterized in that: The adjustable lens includes two coaxially spaced annular plates and a plurality of sliding plates disposed between the two annular plates. The inner walls of the two annular plates are located on the same columnar virtual surface. The sliding plates have a tip extending into the virtual surface and a tail clamped between the two annular plates. All the sliding plates are evenly distributed around the axis of the virtual surface and the sidewalls of adjacent sliding plates slide against each other, so that all the tips surround the lens aperture on the inner side of the virtual surface. One of the two annular plates can rotate relative to the other around the axis of the virtual surface. When it rotates, it can drive all the sliding plates to move synchronously, causing the lens aperture to expand or shrink. When it stops rotating, it can keep the lens aperture in its current state.

3. The multi-mode ion source according to claim 2, characterized in that: The two annular plates have guide grooves on their facing surfaces, and the two sides of the tail have protrusions that match the guide grooves and are inserted into the guide grooves. When the two annular plates rotate relative to each other, the protrusions can be forced to move through the guide grooves, thereby driving the slide plate to move and thus enlarging or shrinking the lens hole.

4. The multi-mode ion source according to claim 3, characterized in that: The guide groove on one of the annular plates is a long straight groove, and the guide groove on the other annular plate is an arc-shaped groove. The protrusion on the tail that matches the long straight groove is a strip-shaped protrusion, and the protrusion that matches the arc-shaped groove is a column-shaped protrusion.

5. The multi-mode ion source according to claim 4, characterized in that: The long straight groove extends tangentially along the inner hole of the annular plate in which it is located, the strip-shaped protrusion is slidably inserted into the long straight groove, the arc-shaped groove penetrates the annular plate in the thickness direction, and the columnar protrusion is slidably and rotatably inserted into the arc-shaped groove.

6. The multi-mode ion source according to claim 2, characterized in that: One of the annular plates has an outwardly extending push rod on its outer circumferential surface, the push rod being used to drive the annular plate to rotate relative to the other annular plate.

7. The multi-mode ion source according to claim 6, characterized in that: The multi-mode ion source also includes a drive assembly for driving the push rod, the drive assembly including a motor.

8. The multi-mode ion source according to claim 2, characterized in that: The two side walls of the tip are flat surfaces, and the hole is a regular polygonal hole.

9. The multi-mode ion source according to claim 2, characterized in that: Both the annular plate and the sliding plate are conductive metal plates.

10. The multi-mode ion source according to claim 1, characterized in that: The filament assembly includes an inner filament cover, an outer filament shield, and a filament disposed between the filament cover and the filament shield. The transmission assembly includes a quadrupole transmission assembly and an octupole transmission assembly.

11. The multi-mode ion source according to claim 1, characterized in that: The lens assembly also includes a conventional lens, and the adjustable lens is the one closest to the filament assembly in the lens assembly.

12. A mode switching method for a multi-mode ion source, wherein the multi-mode ion source is the multi-mode ion source according to any one of claims 1 to 11, characterized in that: When it is necessary to switch the multi-mode ion source to EI mode, the reaction gas is turned off first and then the lens aperture is enlarged to reduce the gas pressure in the collision chamber; when it is necessary to switch the multi-mode ion source to CI mode, the lens aperture is narrowed first and then the reaction gas is introduced to increase the gas pressure in the collision chamber.

13. The mode switching method for a multi-mode ion source according to claim 12, characterized in that: When it is necessary to switch the multimode ion source to the transition mode, the lens aperture is gradually reduced from the maximum size, and the reaction gas is gradually introduced during this process. When a clean spectrum with the required resolution and repeatability is found, the size of the lens aperture is maintained at the current state, and the gas pressure of the reaction gas is stabilized.

14. The mode switching method for a multi-mode ion source according to claim 12, characterized in that: The expansion and contraction of the lens aperture are electrically adjustable. At any time during the expansion or contraction of the lens aperture, the electric adjustment can be stopped to maintain the size of the lens aperture in its current state.

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