Mass spectrometer and method applied thereby for reducing ion loss and succeeding stage vacuum load
The disclosure relates to a mass spectrometer and a method applied thereby for reducing ion loss and succeeding stage vacuum load. The mass spectrometer includes an ion source connected via vacuum interfaces, a vacuum chamber and a succeeding stage device; wherein a tubular lens is arranged above a Mach disc formed by a gas flow carrying ions at the vacuum interfaces, so that an ion transfer path is restrained and the ions scattering with the gas flow is reduced. In comparison to a sole reliance on a radio-frequency voltage for focusing ions, the efficiency of ion capture in a jet region is improved by using an aerodynamic lens; and the desolvation efficiency of electrically charged droplets is also improved, thereby further improving the sensitivity of the mass spectrometer. Meanwhile the tubular aerodynamic lens is simple in structure and small in size.
1. A mass spectrometer, comprising:
an ion source, located in a first gas pressure region and providing ions;
a vacuum chamber, having an inlet and an outlet and located in a second gas pressure region having a gas pressure lower than that of said first gas pressure region; wherein ions in said first gas pressure region are allowed to pass through said inlet of said vacuum chamber and enter said vacuum chamber located in said second gas pressure region along with a gas flow generated by a pressure difference, and exit said vacuum chamber from said outlet of said vacuum chamber;
an ion guiding device, arranged in said vacuum chamber and located at a succeeding stage of said vacuum chamber inlet but a preceding stage of said vacuum chamber outlet; and
a hollow tubular lens, arranged in said vacuum chamber and located at said succeeding stage of said vacuum chamber inlet but said preceding stage of said ion guiding device;
wherein said tubular lens is an aerodynamic lens whose central axis is parallel to a direction of said gas flow entering said vacuum chamber from said inlet of said vacuum chamber, said gas flow produces a Mach disc as a result of a free expanded jet after entering said vacuum chamber, and the inlet of said tubular lens is located at the upstream part of said Mach disc.
2. The mass spectrometer according to claim 1 , characterized in that said free expanded gas flow is caused to form at least one vortex region at the downstream part of said Mach disc by said tubular lens.
3. The mass spectrometer according to claim 1 , characterized in that said tubular lens lead the outer side of said free expanded gas flow to form a vortex sheath, and said vortex sheath starts from an axial tail end of said tubular lens.
4. The mass spectrometer according to claim 1 , characterized in that said tubular lens is made of insulating material.
5. The mass spectrometer according to claim 1 , characterized in that said tubular lens contains a metal electrode.
6. The mass spectrometer according to claim 5 , characterized in that said metal electrode is a metal cylinder and is applied with a DC voltage.
7. The mass spectrometer according to claim 5 , characterized in that said metal electrode is a multipole and is applied with a radio-frequency voltage and the DC voltage, and said multipole has an axis substantially coinciding with said central axis of the tubular lens.
8. The mass spectrometer according to claim 5 , characterized in that said metal electrode is a stacked-ring electrode array distributed along said central axis of said tubular lens, and is applied with the radio-frequency voltage and the DC voltage.
9. The mass spectrometer according to claim 5 , characterized in that said metal electrode is a part of said ion guiding device.
10. The mass spectrometer according to claim 1 , characterized in that said tubular lens has a length-to-diameter ratio ranging from 0.5 to 5.
11. The mass spectrometer according to claim 1 , characterized in that a hollow part of said tubular lens has a diameter varying in an axial direction.
12. The mass spectrometer according to claim 11 , characterized in that said hollow part of said tubular lens comprises one or more sections having a reduced diameter in the axial direction.
13. The mass spectrometer according to claim 1 , characterized in that said vacuum chamber inlet or outlet is a capillary or a small hole or a sampling cone hole or a nozzle or a combination of the above.
14. The mass spectrometer according to claim 1 , characterized in that a pressure ratio of said first gas pressure region to said second gas pressure region is greater than 2.
15. The mass spectrometer according to claim 1 , characterized in that a ratio between a minimum inner diameter of said tubular lens and a minimum inner diameter of a tail end of said vacuum chamber inlet is anyone of the following ranges: (a)1 to 2, (b)2 to 4, (c)4 to 8 and (d)8 to 20.
16. The mass spectrometer according to claim 1 , characterized in that a ratio between an axial distance from the tail end of said vacuum chamber inlet to the tail end of said tubular lens and the axial distance from the tail end of said vacuum chamber inlet to a first Mach disc therebehind is 1 to 2.
17. A method for reducing ion loss occurring with free expansion of the gas flow when said ions pass through vacuum interfaces of the mass spectrometer, comprising:
providing an ion source which is located in the first gas pressure region and provides the ions;
providing the vacuum chamber located in the second gas pressure region having the gas pressure lower than that of said first gas pressure region, wherein the ions in said first gas pressure region are allowed to pass through the inlet of said vacuum chamber and enter said vacuum chamber located in said second gas pressure region along with said gas flow generated by a pressure difference, and exit said vacuum chamber from the outlet of said vacuum chamber;
providing the ion guiding device arranged in said vacuum chamber and located at the succeeding stage of said vacuum chamber inlet but the preceding stage of said vacuum chamber outlet; and
providing the hollow tubular lens arranged in said vacuum chamber and located at the succeeding stage of said vacuum chamber inlet but the preceding stage of said ion guiding device, wherein said tubular lens is an aerodynamic lens whose central axis is parallel to the direction of said gas flow entering said vacuum chamber from said inlet of said vacuum chamber, said gas flow produces the Mach disc as a result of said free expanded jet after entering said vacuum chamber, and the inlet of said tubular lens is located at the upstream part of said Mach disc.
18. The method according to claim 17 , characterized in that said free expanded gas flow is caused to form at least one vortex region at the downstream part of the Mach disc by said tubular lens.
19. A method for reducing the vacuum load of the succeeding stage in a multistage vacuum system of the mass spectrometer, characterized in that a vortex sheath is caused to form at on the outer side of a free expanded gas flow beam by said tubular lens of said mass spectrometer according to claim 1 so as to effectively direct at least a part of a central gas flow beam towards an off-axis direction, thereby reducing the amount of the gas flow at a succeeding stage vacuum interface located in a paraxial region.