Underexpansion jet vacuum ultraviolet light ionization source

Abstract

The invention discloses an under-expansion jet vacuum ultraviolet light ionization source which comprises a sample injection pipeline, a coaxial sample injector, a vacuum ultraviolet light source, an under-expansion jet ionizer, an insulating exhaust ring, a focusing differential electrode, an insulating ring, a cavity, a vacuum pump set and the like. Sample gas enters the coaxial sample injector through the sample injection pipeline, is stably and coaxially introduced into the under-expansion jet ionizer, and is ionized into ions by vacuum ultraviolet light in a high-pressure ionization region of the under-expansion jet ionizer, and the ions enter a low-pressure scattering region after passing through the sound velocity flow limiting hole, so that the ions are separated from the under-expansion jet ionizer. Under the action of the under-expansion jet flow in the scattering area and the focusing electric field between the ionizer and the focusing differential electrode, ions are quickly transmitted into the back-stage vacuum in a focusing manner, and redundant gas is pumped out by the vacuum pump set through the insulating exhaust ring. According to the ionization source, the problems of shock wave interference generated by a traditional jet technology, collision induced dissociation generated by a radio frequency transmission technology and the like are solved, and ion transmission under high air pressure is effectively improved.

Description

Technical Field

[0001] The 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 is a soft ionization technology with high molecular ion yield and low fragmentation. It can ionize polar and non-polar compounds and is a universal ionization method. Based on this technology, vacuum ultraviolet photoionization mass spectrometry has the advantages of simple mass spectra and no matrix effect. It can effectively detect compounds in complex systems and has received widespread attention and application in recent years.

[0003] As the core component of the 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 zone is an important method to improve the detection sensitivity of the vacuum ultraviolet photoionization mass spectrometer. However, high ionization pressure leads to frequent ion-molecule collisions, which limits the efficiency of ion transmission. At present, radio frequency electric field focusing technology is usually 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 way to improve ion transport under high pressure. In order to reduce ion diffusion, jets are often used to reduce ion transmission time. However, in conventional jet transmission technology, the jet is formed in the continuous flow area, which will produce obvious shock wave structures and seriously interfere with ion transmission. Conical hole sampling in the silent zone before the shock wave is formed, although it avoids shock wave interference, it causes obvious ion sampling losses. Lowering the air pressure in the jet area will cause the jet to change from a shock wave structure to a shock-free structure dominated by a scattering mechanism, eliminating shock wave interference, which is expected to overcome the above problems. Summary of the invention

[0005] The present invention proposes an underexpanded jet vacuum ultraviolet photoionization source, which cooperates with a vacuum ultraviolet light source to perform photoionization in the high-pressure ionization zone of the underexpanded jet ionizer to obtain a high ion yield. At the same time, the air pressure in the low-pressure scattering zone of the underexpanded jet ionizer is reduced to a transition flow or molecular flow state to form an underexpanded jet in the scattering region without a shock wave structure. In the low-pressure scattering zone, ions efficiently pass through the focusing differential electrode under the combined action of the jet and the focusing electric field and enter the post-stage vacuum, thereby obtaining a high ion transmission efficiency.

[0006] The technical scheme of the embodiment of the present invention is: an underexpanded jet vacuum ultraviolet photoionization source, 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 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 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; the sampling pipeline 1, the coaxial sampler 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 a cavity 8, and the focusing differential electrode 6 is coaxially fixed to 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 a vacuum pump group 9; the vacuum pump group 9 provides a large pumping speed to form an underexpanded jet in the scattering area.

[0007] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. Use a small-sized sonic limiting hole and a high-speed vacuum pump to obtain a high pressure ratio between the high-pressure ionization zone and the low-pressure scattering zone of the underexpanded jet ionizer. At the same time, reduce the pressure in the low-pressure scattering zone of the underexpanded jet ionizer to form an underexpanded jet in the scattering area without a shock wave structure, which helps achieve high ion transmission efficiency.

[0008] 2. Using the high-pressure ionization region of the underexpanded jet ionizer as the photoionization region can obtain a high ion yield under high pressure.

[0009] 3. By applying voltages 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.

[0010] 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.

[0011] 5. The sample gas is smoothly and coaxially introduced into the underexpanded jet ionizer through the coaxial injector to eliminate possible turbulent interference.

[0012] 6. Compared with RF 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.

[0013] 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

[0014] Figure 1 It is a schematic structural diagram of an underexpanded jet vacuum ultraviolet photoionization source in an embodiment of the present invention.

[0015] Description of reference numerals: 1. Injection pipeline; 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

[0016] 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 protection scope of the present invention.

[0017] 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: a sample injection pipeline 1, a coaxial sample 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.

[0018] The sample gas enters the coaxial injector 2 through the injection line 1, and then smoothly coaxially enters the high-pressure ionization zone 41 of the underexpanded jet ionizer 4, and is ionized into ions after being irradiated by the vacuum ultraviolet light source 3. In the low-pressure scattering zone 43 of the underexpanded jet ionizer 4, the ions are affected by the underexpanded jet in the scattering area and the focusing electric field between the underexpanded jet ionizer 4 and the focusing differential electrode 6, and quickly and concentratedly pass through the differential hole of the focusing differential electrode 6 and enter the post-stage vacuum. The excess gas is pumped away by the vacuum pump group 9 connected to the cavity 8 through the insulating exhaust ring 5.

[0019] Furthermore, the size of the sample injection pipeline 1 can be adjusted so that the sample gas injection volume matches the ionization source working gas pressure.

[0020] 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.

[0021] 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 under-expanded jet ionizer 4; an annular groove is provided on the lower bottom surface to form an annular buffer zone for smoothly and coaxially introducing the injection gas into the under-expanded jet ionizer 4.

[0022] Furthermore, the vacuum ultraviolet light source 3 can be a low-pressure discharge lamp, a laser, a synchrotron radiation light source, etc., and the sample gas molecules are ionized by the vacuum ultraviolet light emitted by the light source. Since low-pressure inert gas discharge lamps have the advantages of compact structure and easy use, it is preferred to use low-pressure inert gas discharge lamps, such as krypton lamps.

[0023] Furthermore, the air pressure in the high-pressure ionization zone 41 of the underexpanded jet ionizer 4 is above 100 Pa, and the air pressure in the low-pressure scattering zone 43 is below 10 Pa, so as to form an underexpanded jet in the scattering region and simultaneously obtain high ionization pressure and low scattering zone pressure.

[0024] Furthermore, the high-pressure ionization zone 41 of the underexpanded jet ionizer 4 can be cylindrical, truncated cone, etc. Since the truncated cone has a continuously changing cross-section, it is preferred to use a long truncated cone ionization zone with a small angle between the side and the axis to obtain a smooth transition to the sonic flow limiting hole 42. At the same time, the coaxially placed vacuum ultraviolet light source 3 is used to obtain a long vacuum ultraviolet optical path and a high beam overlap factor.

[0025] 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 zone and the low pressure scattering zone.

[0026] 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.

[0027] Furthermore, the underexpanded jet ionizer 4 and the focusing differential electrode 6 may apply voltages respectively to form an ion focusing electric field in the scattering region.

[0028] Furthermore, the focusing differential electrode 6 has a central differential hole with a cone angle for matching the back-stage vacuum and transmitting ions, and is coaxially fixed with the ion transmission opening in the cavity 8 through an insulating ring 7.

[0029] 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.

[0030] Furthermore, the cavity 8 has a plurality of openings for connecting the vacuum pump group 9, the sample injection pipeline 1, the subsequent ion transmission, etc.

[0031] Furthermore, the vacuum pump group 9 is composed of a molecular pump with a large pumping speed and a fore pump to provide a sufficient pumping speed for forming an underexpanded jet.

[0032] 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.

[0033] Furthermore, the size of the sample inlet pipeline 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.

[0034] 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.

[0035] 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 gas pressure, preferably with an annular groove depth of 5 mm and an annular width of 3 mm.

[0036] Furthermore, the vacuum ultraviolet light source 3 ionizes the gas molecules and may 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.

[0037] 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 zone 41 is 30 mm long, the side angle with the axis is 30 degrees, the low-pressure scattering zone 43 is 10 mm long, the side angle with the axis is 60 degrees, and the inner diameter of the sonic limiting hole 42 is 2 mm.

[0038] 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, preferably 15 V and 13 V, respectively.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Furthermore, the cavity 8 is provided with an inlet port, a vacuum pumping port, and an ion transmission port, the inlet port is connected to the inlet pipe 1, and the vacuum pumping port is connected to the vacuum pump group 9. The air pressure in the cavity is generally maintained below ten Pa, which is used to form an underexpanded jet in the scattering area.

[0043] 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 molecular pump with a high pumping speed greater than 100 L / s and a fore-stage mechanical pump combination.

[0044] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

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 to introduce sample gas; the injection pipeline (1) is installed on the coaxial injector (2); the coaxial injector (2) is used to coaxially and stably introduce 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 ionizer (4); expansion 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); the focusing differential electrode (6) is coaxially fixed to 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 a vacuum pump group (9); the vacuum pump group (9) provides a large exhaust speed to form an underexpanded jet in the 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 sample injector (2) has an annular buffer zone and a sealed fixing zone. The annular buffer zone is used to coaxially and smoothly introduce the sample gas into the underexpanded jet ionizer (4); the sealed fixing 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) comprises a high-pressure ionization zone (41), a sonic flow limiting hole (42), and a low-pressure scattering zone (43). The gas is in a continuous flow state in the high-pressure ionization zone (41) with a pressure above 100 Pa, reaches the speed of sound in the sonic flow limiting hole (42), and is in a transitional flow or molecular flow state in the low-pressure scattering zone (43) with a pressure below 10 Pa, so as to form an underexpanded jet in the low-pressure scattering zone.

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 light path; the inner diameter of the sonic flow limiting hole (42) is less than 5 mm, so as 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, so as to reduce the ion transmission distance.

6. 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) is in the shape of a long truncated cone with a small angle between the side and the axis, and is used to obtain an airflow that smoothly transitions to the sonic flow limiting hole (42). The low-pressure scattering zone (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 zone (43) and the focusing differential electrode (6) form a focusing electric field, radially confining ions in the underexpanded jet for focusing. The sonic flow limiting hole (42) is located between the high-pressure ionization zone (41) and the low-pressure scattering zone (43), and has a small aperture to assist in forming a high pressure ratio between the ionization zone and the scattering zone.

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 for exhausting excess gas; the gas is pumped out by a vacuum pump group (9) to maintain a low pressure state in the low pressure scattering region (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-stage vacuum to transmit ions into the rear-stage 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 sample 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 zone (41) is 30 mm long, with a side angle of 30 degrees to the axis, the low-pressure scattering zone (43) is 10 mm long, with a side angle of 60 degrees to the axis, and 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 exhaust holes with a length of 3 mm 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; and the opening size of the cone angle is set to 90 degrees.

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