An underexpanded jet vacuum ultraviolet photoionization source

Abstract

The present invention discloses an underexpanded jet vacuum ultraviolet photoionization source, comprising an inlet pipe, a coaxial injector, a vacuum ultraviolet light source, an underexpanded jet ionizer, an insulating exhaust ring, a focusing differential electrode, an insulating ring, a cavity, and a vacuum pump assembly. Sample gas enters the coaxial injector through the inlet pipe and is smoothly and coaxially introduced into the underexpanded jet ionizer. In the high-pressure ionization zone of the underexpanded jet ionizer, the sample gas is ionized into ions by vacuum ultraviolet light. After passing through a sonic velocity limiting orifice, the ions enter a low-pressure scattering zone. Under the action of the underexpanded jet in the scattering zone and the focusing electric field between the ionizer and the focusing differential electrode, the ions are rapidly and focusedly transmitted into a post-stage vacuum. Excess gas is pumped out by the vacuum pump assembly through the insulating exhaust ring. This ionization source overcomes the problems of shock wave interference generated by traditional jet technology and collision-induced dissociation generated by radio frequency transmission technology, effectively improving ion transmission under high pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of photoionization analysis and detection and mass spectrometry, and in particular to an underexpanded jet vacuum ultraviolet photoionization source, which is used for high-efficiency generation and extraction of ions in a vacuum ultraviolet photoionization source. Background Art

[0002] Vacuum ultraviolet photoionization (VUV) is a soft ionization technique with high molecular ion yield and minimal fragmentation. It is capable of ionizing both polar and non-polar compounds, making it a versatile ionization method. Based on this technique, VUV photoionization mass spectrometry offers the advantages of simple mass spectra and no matrix effects, enabling the effective detection of compounds in complex systems. It has garnered widespread attention and application in recent years.

[0003] As the core component of a mass spectrometer, the vacuum ultraviolet photoionization source is used to generate ions and transmit them into the mass analyzer. Generally speaking, increasing the gas pressure in the ionization region is an important method to improve the detection sensitivity of vacuum ultraviolet photoionization mass spectrometry. However, high ionization pressure leads to frequent ion-molecule collisions, which limits the efficiency of ion transmission. Currently, radio frequency electric field focusing technology is commonly used for ion transmission under high pressure. However, this technology still has problems: on the one hand, the use of radio frequency electric field brings about collision-induced dissociation and mass discrimination effects during ion transmission; on the other hand, the radio frequency power supply required for the radio frequency electric field also increases the cost and power consumption of the system.

[0004] Optimizing the flow field is another approach to improving ion transport at high pressures. To reduce ion diffusion, jets are often used to shorten ion transport time. However, in conventional jet transport techniques, the jet forms in the continuous flow region, generating a significant shock wave structure that severely interferes with ion transport. While conical hole sampling in the silent zone before shock wave formation avoids shock wave interference, it results in significant ion sampling loss. Lowering the pressure in the jet region transforms the jet from a shock wave structure to a shock-free structure dominated by scattering mechanisms, eliminating shock wave interference and potentially overcoming this problem. Summary of the Invention

[0005] The present invention proposes an underexpanded jet vacuum ultraviolet photoionization source. Combined with a vacuum ultraviolet light source, it performs photoionization in the high-pressure ionization zone of the underexpanded jet ionizer, achieving a high ion yield. Simultaneously, the pressure in the low-pressure scattering zone of the underexpanded jet ionizer is reduced to a transitional flow or molecular flow state, forming an underexpanded jet with a scattering region free of shock wave structures. Within the low-pressure scattering zone, ions, under the combined action of the jet and the focusing electric field, efficiently pass through the focusing differential electrode and enter the post-stage vacuum, achieving high ion transmission efficiency.

[0006] The technical solution of the embodiment of the present invention is: an underexpanded jet vacuum ultraviolet photoionization source, which includes an injection pipeline 1, a coaxial injector 2, a vacuum ultraviolet light source 3, an underexpanded jet ionizer 4, an insulating exhaust ring 5, a focusing differential electrode 6, an insulating ring 7, a cavity 8, and a vacuum pump group 9; wherein the injection pipeline 1 is used to introduce sample gas; the injection pipeline 1 is installed on the coaxial injector 2; the coaxial injector 2 is used to coaxially and smoothly introduce the sample gas into the underexpanded jet ionizer 4, one side of the coaxial injector 2 is fixed with the vacuum ultraviolet light source 3, and the other side is connected to the underexpanded jet ionizer 4; the vacuum ultraviolet light source 3 is used to provide vacuum ultraviolet light; the vacuum ultraviolet light is incident on the underexpanded jet ionizer 4 through the central hole of the coaxial injector 2, The underexpanded jet ionizer 4 is used to form an underexpanded jet; the underexpanded jet ionizer 4 is connected to the focusing differential electrode 6; an insulating exhaust ring 5 is arranged between the underexpanded jet ionizer 4 and the focusing differential electrode 6 for exhausting excess gas; the sampling pipeline 1, the coaxial sample injector 2, the vacuum ultraviolet light source 3, the underexpanded jet ionizer 4, the insulating exhaust ring 5, the focusing differential electrode 6, and the insulating ring 7 are connected and arranged in the cavity 8, and the focusing differential electrode 6 is coaxially fixed with the ion transmission opening of the cavity 8 through the insulating ring 7; the cavity 8 is respectively provided with a sampling pipeline opening, a vacuum exhaust port, and an ion transmission port, the sampling pipeline opening is connected to the sampling pipeline 1, and the vacuum exhaust port is connected to the vacuum pump group 9; the vacuum pump group 9 provides a high pumping speed to form an underexpanded jet in the scattering area.

[0007] The technical solution of the present invention has the following beneficial effects compared with the prior art:

[0008] 1. A small-sized sonic flow-limiting orifice and a high-speed vacuum pump are used to obtain a high pressure ratio between the high-pressure ionization region and the low-pressure scattering region of the underexpanded jet ionizer. At the same time, the pressure in the low-pressure scattering region of the underexpanded jet ionizer is reduced to form an underexpanded jet in the scattering region without a shock wave structure, thereby assisting in achieving high ion transmission efficiency.

[0009] 2. Using the high-pressure ionization region of the underexpanded jet ionizer as the photoionization region can obtain a high ion yield at high pressure.

[0010] 3. By applying voltage to the underexpanded jet ionizer and the focusing differential electrode respectively, a focusing electric field is formed in the scattering region to assist in focusing ions and achieve high ion transmission efficiency.

[0011] 4. The long high-pressure ionization region and short low-pressure scattering region of the underexpanded jet ionizer are conducive to obtaining a long optical path and a short ion transmission path to improve the performance of the ionization source.

[0012] 5. The sample gas is smoothly and coaxially introduced into the underexpanded jet ionizer through the coaxial injector to eliminate possible turbulent interference.

[0013] 6. Compared with radio frequency electric field focusing technology, it reduces the potential mass discrimination effect in ion transmission, reduces the adverse effects of high-energy ion-molecule collisions, and reduces the cost and power consumption of the system.

[0014] 7. Compared with conventional jet ion transmission technology, it avoids the ion loss caused by shock wave structure and the sampling loss caused by silent zone sampling. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a structural schematic diagram of an underexpanded jet vacuum ultraviolet photoionization source in an embodiment of the present invention.

[0016] Description of reference numerals:

[0017] 1. Injection pipe; 2. Coaxial injector; 3. Vacuum ultraviolet light source; 4. Underexpanded jet ionizer; 5. Insulating exhaust ring; 6. Focusing differential electrode; 7. Insulating ring; 8. Cavity; 9. Vacuum pump group; 41. High-pressure ionization zone; 42. Sonic velocity limiting hole; 43. Low-pressure scattering zone. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] According to one embodiment of the present invention, there is provided an underexpanded jet vacuum ultraviolet photoionization source, such as Figure 1 As shown, it includes: an injection pipeline 1, a coaxial injector 2, a vacuum ultraviolet light source 3, an underexpanded jet ionizer 4, an insulating exhaust ring 5, a focusing differential electrode 6, an insulating ring 7, a cavity 8, and a vacuum pump group 9.

[0020] The sample gas enters the coaxial injector 2 through the inlet line 1 and then smoothly and coaxially enters the high-pressure ionization zone 41 of the underexpanded jet ionizer 4. After being irradiated by the vacuum ultraviolet light source 3, it is ionized into ions. In the low-pressure scattering zone 43 of the underexpanded jet ionizer 4, the ions are affected by the underexpanded jet in the scattering region and the focusing electric field between the underexpanded jet ionizer 4 and the focusing differential electrode 6. They are rapidly and concentratedly transported through the differential aperture of the focusing differential electrode 6 and enter the post-stage vacuum. Excess gas is evacuated via the insulating exhaust ring 5 to the vacuum pump assembly 9 connected to the chamber 8.

[0021] Furthermore, the size of the sample injection pipeline 1 can be adjusted so that the sample gas injection volume matches the ionization source working pressure.

[0022] Furthermore, the injection pipeline 1 is installed on the side of the coaxial injector 2, and its outlet is located in the annular buffer zone of the coaxial injector.

[0023] Furthermore, the coaxial injector 2 is cylindrical as a whole, and a concentric sealing and fixing area is provided on the upper bottom surface for installing the vacuum ultraviolet light source 3 or the window; a through hole is provided in the center for introducing vacuum ultraviolet light into the underexpanded jet ionizer 4; and an annular groove is provided on the lower bottom surface to form an annular buffer zone for smoothly and coaxially introducing the sample gas into the underexpanded jet ionizer 4.

[0024] Furthermore, the vacuum ultraviolet light source 3 can be a low-pressure discharge lamp, a laser, a synchrotron radiation source, or the like. The sample gas molecules are ionized by the vacuum ultraviolet light emitted by the light source. Low-pressure inert gas discharge lamps, such as krypton lamps, are preferred due to their compact structure and ease of use.

[0025] Furthermore, the pressure in the high-pressure ionization zone 41 of the underexpanded jet ionizer 4 is above 100 Pa, and the pressure in the low-pressure scattering zone 43 is below 10 Pa, so as to form an underexpanded jet in the scattering area and simultaneously obtain high ionization pressure and low scattering zone pressure.

[0026] Furthermore, the high-pressure ionization region 41 of the underexpanded jet ionizer 4 can be cylindrical, truncated cone, or the like. Since the truncated cone has a continuously varying cross-section, a long truncated cone-shaped ionization region with a small angle between the side and the axis is preferred to ensure a smooth transition of the airflow to the sonic flow limiting orifice 42. Simultaneously, in conjunction with the coaxially placed vacuum ultraviolet light source 3, a long vacuum ultraviolet optical path and a high beam overlap factor are achieved.

[0027] Furthermore, the sonic flow limiting hole 42 of the underexpanded jet ionizer 4 has a small aperture to assist in forming a high pressure ratio between the high-pressure ionization region and the low-pressure scattering region.

[0028] Furthermore, the low-pressure scattering region 43 of the underexpanded jet ionizer 4 is in the shape of a short truncated cone with a large angle between the side and the axis, so as to form a wide-range focusing electric field and reduce the ion transmission distance.

[0029] Furthermore, voltages may be applied to the underexpanded jet ionizer 4 and the focusing differential electrode 6 respectively to form an ion focusing electric field in the scattering region.

[0030] Furthermore, the focusing differential electrode 6 has a central differential hole with a cone angle for matching the post-stage vacuum and transmitting ions, and is coaxially fixed with the ion transmission opening in the cavity 8 through an insulating ring 7.

[0031] Furthermore, the insulating exhaust ring 5 separates the underexpanded jet ionizer 4 and the focusing differential electrode 6 , while allowing excess gas to be extracted through the exhaust hole.

[0032] Furthermore, the cavity 8 has multiple openings for connecting the vacuum pump group 9, the sample injection pipeline 1, the subsequent ion transmission, etc.

[0033] Furthermore, the vacuum pump group 9 is composed of a molecular pump with a high pumping speed and a backing pump to provide a sufficient pumping speed for forming an underexpanded jet.

[0034] Furthermore, the coaxial injector 2, vacuum ultraviolet light source 3, underexpanded jet ionizer 4, insulating exhaust ring 5, focusing differential electrode 6, and insulating ring 7 are coaxially mounted and fixed on the inner wall of the cavity 8, and the inner holes of each component are also coaxial, and the connection is sealed with a rubber ring.

[0035] Furthermore, the size of the sample inlet line 1 can be adjusted to match the ionization source gas pressure, preferably with an inner diameter of 200 μm and a length of 100 mm.

[0036] Furthermore, the central through hole of the coaxial injector 2 can be adjusted according to the beam size of the vacuum ultraviolet light source, preferably 6 mm.

[0037] Furthermore, the annular buffer zone of the coaxial injector 2 can be adjusted according to the injection flow rate, the size of the ionizer and the working pressure, and preferably the annular groove depth is 5 mm and the annular width is 3 mm.

[0038] Furthermore, the vacuum ultraviolet light source 3 ionizes the gas molecules and can be a laser, a vacuum ultraviolet discharge lamp, a synchrotron radiation light source, etc. In the present invention, a vacuum ultraviolet discharge lamp is preferably used.

[0039] Furthermore, the size of the underexpanded jet ionizer 4 can be adjusted according to the cavity geometry and the overall design of the mass spectrometer. Preferably, the high-pressure ionization region 41 is 30 mm long, the side angle to the axis is 30 degrees, the low-pressure scattering region 43 is 10 mm long, the side angle to the axis is 60 degrees, and the inner diameter of the sonic flow limiting hole 42 is 2 mm.

[0040] Furthermore, the voltages of the underexpanded jet ionizer 4 and the focusing differential electrode 6 can be adjusted according to the jet state and the subsequent ion transmission parameters, and are preferably 15 V and 13 V, respectively.

[0041] Furthermore, the insulating exhaust ring 5 can be made of insulating materials such as polyetheretherketone (PEEK), polytetrafluoroethylene, ceramics, etc., preferably PEEK; its thickness can be adjusted according to the jet state, preferably 4 mm; the size of its exhaust holes affects the cavity air pressure and thus affects the jet state, preferably 8 3 mm exhaust holes on the side.

[0042] Furthermore, the diameter of the central differential hole of the focusing differential electrode 6 can be adjusted to match the post-stage vacuum, preferably 1.5 mm; the opening size of the cone angle is preferably 90 degrees.

[0043] Furthermore, the insulating ring 7 can be made of insulating materials such as PEEK, polytetrafluoroethylene, ceramics, etc., preferably PEEK; the thickness is preferably 1 mm.

[0044] Furthermore, cavity 8 is provided with an inlet for a sample feed, a vacuum pumping port, and an ion transmission port. The inlet for a sample feed is connected to the sample feed line 1, and the vacuum pumping port is connected to a vacuum pump assembly 9. The pressure in the cavity is generally maintained below 10 Pa to form an underexpanded jet in the scattering region.

[0045] Furthermore, the vacuum pump group 9 provides a high pumping speed to form an underexpanded jet in the scattering region. The present invention preferably uses a combination of a molecular pump with a high pumping speed greater than 100 L / s and a fore-stage mechanical pump.

[0046] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. An underexpanded jet vacuum ultraviolet photoionization source, characterized in that: The ionization source comprises an injection pipeline (1), a coaxial injector (2), a vacuum ultraviolet light source (3), an underexpanded jet ionizer (4), an insulating exhaust ring (5), a focusing differential electrode (6), an insulating ring (7), a cavity (8), and a vacuum pump group (9); wherein the injection pipeline (1) is used for introducing sample gas; the injection pipeline (1) is installed on the coaxial injector (2); the coaxial injector (2) is used for coaxially and stably introducing sample gas into the underexpanded jet ionizer (4); one side of the coaxial injector (2) is fixed with the vacuum ultraviolet light source (3), and the other side is connected to the underexpanded jet ionizer (4); the vacuum ultraviolet light source (3) is used for providing vacuum ultraviolet light; the vacuum ultraviolet light is incident on the underexpanded jet ionizer (4) through the central hole of the coaxial injector (2), and the underexpanded jet ionizer (4) is used for forming an underexpanded jet ionizer (4). An expansion jet; an underexpanded jet ionizer (4) is connected to a focusing differential electrode (6); an insulating exhaust ring (5) is provided between the underexpanded jet ionizer (4) and the focusing differential electrode (6) for exhausting excess gas; an injection line (1), a coaxial injector (2), a vacuum ultraviolet light source (3), an underexpanded jet ionizer (4), an insulating exhaust ring (5), a focusing differential electrode (6), and an insulating ring (7) are connected and arranged in a cavity (8); the focusing differential electrode (6) is coaxially fixed to an ion transmission opening of the cavity (8) through the insulating ring (7); an injection line port, a vacuum exhaust port, and an ion transmission port are respectively provided on the cavity (8); the injection line port is connected to the injection line (1), and the vacuum exhaust port is connected to a vacuum pump group (9); the vacuum pump group (9) provides a high pumping speed to form an underexpanded jet in a scattering area.

2. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The sample gas is introduced into the coaxial injector (2) through the injection line (1), and the connection is sealed with a rubber ring.

3. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The coaxial injector (2) has an annular buffer zone and a sealed fixed zone. The annular buffer zone is used to coaxially and smoothly introduce the sample gas into the underexpanded jet ionizer (4); the sealed fixed zone is used to fix the vacuum ultraviolet light source (3) or the window.

4. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The underexpanded jet ionizer (4) has a high-pressure ionization region (41), a sonic flow limiting hole (42), and a low-pressure scattering region (43). The gas is in a continuous flow state in the high-pressure ionization region (41) with a pressure above 100 Pa, reaches the speed of sound in the sonic flow limiting hole (42), and is in a transition flow or molecular flow state in the low-pressure scattering region (43) with a pressure below 10 Pa, so as to form an underexpanded jet in the low-pressure scattering region.

5. The underexpanded jet vacuum ultraviolet photoionization source according to claim 4, characterized in that: The high-pressure ionization zone (41) of the underexpanded jet ionizer (4) has a length greater than or equal to 20 mm, and cooperates with the vacuum ultraviolet light source (3) to form a coaxial long vacuum ultraviolet optical path; the inner diameter of the sonic flow limiting hole (42) is less than 5 mm to cooperate with the high pressure ratio required to form the underexpanded jet; the low-pressure scattering zone (43) has a length less than or equal to 10 mm, which reduces the ion transmission distance.

6. The underexpanded jet vacuum ultraviolet photoionization source according to claim 4, characterized in that: The high-pressure ionization region (41) of the underexpanded jet ionizer (4) is in the shape of a long truncated cone with a small angle between the side and the axis, and is used to obtain a smooth transition of the airflow to the sonic flow limiting hole (42). The low-pressure scattering region (43) of the underexpanded jet ionizer (4) is in the shape of a short truncated cone with a large angle between the side and the axis, and a voltage is applied so that the low-pressure scattering region (43) and the focusing differential electrode (6) form a focusing electric field, radially confining the ions in the underexpanded jet for focusing; the sonic flow limiting hole (42) is located between the high-pressure ionization region (41) and the low-pressure scattering region (43), and its aperture is small to assist in forming a high pressure ratio between the ionization region and the scattering region.

7. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The insulating exhaust ring (5) is made of insulating material and has a plurality of exhaust holes on its side to discharge excess gas; the gas is pumped out by the vacuum pump group (9) to maintain the low pressure state of the low pressure scattering zone (43) of the underexpanded jet ionizer (4).

8. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The center of the focusing differential electrode (6) has a differential hole with a cone angle, and the cone angle opening faces the rear vacuum to transmit ions into the rear vacuum; the insulating ring (7) is made of insulating material and coaxially connects the focusing differential electrode (6) and the ion transmission port on the cavity (8).

9. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: Ions are generated in the high-pressure ionization region (41) of the underexpanded jet ionizer (4), and are affected by the underexpanded jet and the focusing electric field in the low-pressure scattering region (43) of the underexpanded jet ionizer (4), and enter the post-stage vacuum through the focusing differential electrode (6).

10. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The coaxial injector (2), vacuum ultraviolet light source (3), underexpanded jet ionizer (4), insulating exhaust ring (5), focusing differential electrode (6), and insulating ring (7) are coaxially mounted and fixed on the inner wall of the cavity (8). The inner holes of each component are also coaxial, and the joints are sealed with rubber rings.

11. The underexpanded jet vacuum ultraviolet photoionization source according to claim 5, characterized in that: The high-pressure ionization region (41) is 30 mm long, with a side angle of 30 degrees to the axis. The low-pressure scattering region (43) is 10 mm long, with a side angle of 60 degrees to the axis. The inner diameter of the sonic hole is 2 mm.

12. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The voltages of the underexpanded jet ionizer (4) and the focusing differential electrode (6) were set to 15 V and 13 V, respectively.

13. The underexpanded jet vacuum ultraviolet photoionization source according to claim 1, characterized in that: The insulating exhaust ring (5) is made of polyetheretherketone or polytetrafluoroethylene or ceramic; its length is set to 4 mm; the ring width is set to 2 mm; and the exhaust holes thereon are set to be 8 3 mm exhaust holes on the side.

14. The underexpanded jet vacuum ultraviolet photoionization source according to claim 8, characterized in that: The diameter of the central differential hole of the focusing differential electrode (6) is set to 1.5 mm; the opening size of the cone angle is set to 90 degrees.

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