Aperture gas flow restriction

Abstract

A mass spectrometer is disclosed comprising two vacuum chambers maintained at different pressures. The two vacuum chambers are interconnected by a differential pumping aperture. The effective area of the opening between the two vacuum chambers may be varied by rotating a disk having an aperture in front of the differential pumping aperture so as to vary the gas flow rate through the opening and between the two chambers.

Claims

1. A mass spectrometer comprising: two chambers to be maintained at different pressures in use, wherein the two chambers are interconnected by an opening for transmitting ions from one of the chambers to the other of the chambers; a first device for varying the area of the opening so as to vary the gas flow rate through the opening and between the chambers in use; and an ion storage device downstream of said opening, wherein said ion storage device is synchronised with said opening such that ions are transmitted through said opening into said ion storage device when the opening has a large area and ions are prevented from being transmitted through said opening into said ion storage device when the opening has a relatively smaller area or is closed, wherein said first device is arranged and adapted to fill said ion storage device for a defined time by varying the area of the opening and said defined time is predetermined so as to fill said ion storage device with a predetermined number of ions.

2. A mass spectrometer as claimed in claim 1, wherein said defined time is predetermined so as to fill said ion storage device for a predetermined length of time.

3. A mass spectrometer as claimed in claim 1, wherein at least one of said chambers is connected to a vacuum pump for maintaining the chambers at said different pressures.

4. A mass spectrometer as claimed in claim 1, wherein a high gas flow rate is permitted between the chambers when the area of the opening is large and a low gas flow rate is permitted between the chambers when the area of the opening is smaller.

5. A mass spectrometer as claimed in claim 1, wherein the mass spectrometer is configured to vary the area of the opening such that at a first time the area of the opening is set to permit gas to flow between the chambers, and at a second time the opening is closed so as to substantially prevent gas from passing between the chambers.

6. A mass spectrometer as claimed in claim 1, wherein the area of the opening is repeatedly increased and decreased.

7. A mass spectrometer as claimed in claim 1, further comprising an ion guide in one of the chambers which is arranged to guide or focus ions towards the opening so that they may pass through the opening and into the other chamber.

8. A mass spectrometer as claimed in claim 1, further comprising a second device for pulsing ions towards and through said opening, said second device being synchronised with the opening such that ions are pulsed through the opening when the opening is of relatively large area and ions are not pulsed through the opening when the opening is of relatively small area or is closed.

9. A mass spectrometer as claimed in claim 8, wherein said second device comprises a pulsed ion source.

10. A mass spectrometer as claimed in claim 1, wherein said two chambers are separated by a wall and said opening comprises an orifice in said wall.

11. A mass spectrometer as claimed in claim 1, wherein the opening comprises an orifice in a wall between the chambers and the mass spectrometer further comprises an orifice occlusion member, said orifice occlusion member being movable relative to the orifice so as to cover the orifice by varying amounts and thus change the area of said opening by corresponding varying amounts.

12. A mass spectrometer as claimed in claim 11, wherein said orifice occlusion member comprises at least one aperture and a non-apertured portion, and wherein said orifice occlusion member is arranged and adapted such that it is movable between a position where the aperture is relatively more aligned with the orifice so as to increase the area of the opening and a different position wherein the aperture less aligned with the orifice so as to decrease the area of the opening.

13. A mass spectrometer as claimed in claim 11, wherein said orifice occlusion member comprises at least one aperture and a non-apertured portion, and wherein said orifice occlusion member is arranged and adapted such that it is movable between a position where the non-apertured portion covers the orifice to close said opening, and a different position wherein the aperture is at least partially aligned with the orifice such that gas and/or ions can pass through the opening.

14. A mass spectrometer as claimed in claim 1, wherein the opening is provided by an iris, the opening in the iris being variable in diameter.

15. A mass spectrometer as claimed in claim 1, wherein the opening is provided by a deformable conduit and wherein the conduit is compressible or otherwise deformable so as to reduce the area of the opening through the conduit.

16. A method of controlling the gas flow between two chambers in a mass spectrometer that are maintained at different pressures, wherein the two chambers are interconnected by an opening for transmitting ions from one of the chambers to the other of the chambers, the method comprising: varying the area of the opening so as to vary the gas flow rate through the opening and between the chambers to fill said ion storage device for a defined time which is predetermined so as to fill said ion storage device with a predetermined number of ions; providing an ion storage device downstream of said opening; transmitting ions through said opening into said ion storage device when the opening is of relatively large area; and preventing ions from being transmitted through said opening into said ion storage device when the opening has a relatively smaller area or is closed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments of the present invention together with other arrangements given for illustrative purposes only will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1A shows a cross-section of an opening in a conventional skimmer electrode of a mass spectrometer, FIG. 1B shows a cross-section of an opening in a conventional differential pumping aperture of a mass spectrometer and FIG. 1C shows a cross-section of an opening in a conventional sampling orifice of a mass spectrometer;

(3) FIG. 2A shows an embodiment of the present invention wherein the opening comprises a thin orifice plate and the area of the opening is varied using a rotating disk in which there is a short slot and wherein the slot in the disk is aligned with the opening and FIG. 2B shows an embodiment of the present invention wherein the opening comprises a thin orifice plate and the area of the opening is varied using a rotating disk in which there is a short slot and wherein the slot in the disk is unaligned with the opening;

(4) FIG. 3A shows an example of a rotating disk having a circular hole that may be used according to an embodiment of the present invention, FIG. 3B shows an example of a rotating disk having a short slot that may be used according to an embodiment of the present invention, FIG. 3C shows an example of a rotating disk having a long slot that may be used according to an embodiment of the present invention and FIG. 3D shows an example of a rotating disk having multiple slots that may be used according to an embodiment of the present invention; and

(5) FIG. 4 shows an embodiment wherein the preferred device forms a differential pumping aperture between two vacuum chambers wherein an ion trap is located in an upstream vacuum chamber and a quadrupole rod set is located in a downstream vacuum chamber.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(6) Various different types of conventional ion inlets will first be briefly described with reference to FIGS. 1A-1C. FIG. 1A shows a cross-section of a conventional skimmer electrode 1 mounted on a vacuum housing 2. FIG. 1B shows a conventional differential pumping aperture 3 mounted on a vacuum housing 2. FIG. 10 shows a conventional sampling orifice 4 mounted on a vacuum housing 2. The conductance of these apertures and hence the gas flow through the apertures is dependent upon their radius as well as their depth/thickness.

(7) A preferred embodiment of the present invention will now be described.

(8) According to a preferred embodiment of the present invention a thin plate 5 is preferably provided having an orifice 5a as shown in FIG. 2A. The thin plate 5 is preferably mounted against a vacuum chamber 6 such that the only gas flow from one chamber to the other chamber is via the orifice 5a provided in the thin plate 5. The orifice 5a preferably comprises a differential pumping aperture although less preferred embodiments are contemplated wherein the orifice 5a is provided at the entrance to a housing within a vacuum chamber. For example, the orifice 5a may be provided at the entrance to an ion mobility spectrometer or a collision gas cell located within a vacuum chamber. It is not essential therefore that the orifice 5a separates two vacuum chambers, each vacuum chamber being pumped by a vacuum pump.

(9) A spinning/rotating disk 7 is preferably provided in communication with the assembly comprising the thin plate 5 and the vacuum chamber 6. The spinning/rotating disk 7 preferably has a short aperture 7a which is preferably in the form of a slot.

(10) FIG. 2A shows the preferred embodiment at a time when the slot 7a in the rotating disk 7 is aligned with the orifice 5a in the thin plate 5 so that ions may be transmitted through the differential pumping aperture formed by the orifice 5a.

(11) FIG. 2B shows the preferred embodiment of a time when the orifice 5a in the thin plate 5 is occluded by the non-apertured portion of the rotating disk 7. It is apparent that gas is only capable of passing through the orifice 5a from one chamber to the next when the slot 7a in the rotating disk 7 and the orifice 5a in the thin plate 5 are substantially aligned.

(12) At times when the orifice 5a in the thin plate 5 is occluded by the rotating disk 7, no gas flow through the orifice 5a in the thin plate 5 is possible. By rotating the apertured disk 7 it is therefore possible to reduce the average gas flow through the orifice 5a between the chambers and hence reduce the vacuum pump requirements.

(13) Various embodiments are contemplated wherein the apertured disk 7 may take forms other than that shown in FIGS. 2A and 2B. The apertured disk 7 may take the form as shown in FIGS. 3A to 3D. In FIG. 3A the aperture 7a in the disk 7 is in the form of a small hole. In FIG. 3B the aperture 7a in the disk 7 is in the form of a short slot. In FIG. 3C the aperture 7a in the disk 7 is in the form of a long slot. In FIG. 3D multiple apertures 7a are provided in the disk 7 in the form of multiple slots.

(14) According to embodiments of the present invention the rotating disk 7 may not be flat.

(15) According to embodiments of the present invention the rotating disk 7 may additionally and/or alternatively contain protuberances. For example, according to an embodiment the disk 7 may have a short tube or other type of aperture mounted upon it (instead of an aperture 7a in the disk 7).

(16) FIG. 4 shows an embodiment of the present invention showing a section of a mass spectrometer comprising a first vacuum chamber 8 and a second vacuum chamber 9. A linear ion trap 10 is located in the first vacuum chamber 8 and a quadrupole mass filter 11 is located in the second vacuum chamber 9.

(17) A differential pumping aperture between the two vacuum chambers 8,9 is preferably provided by a thin plate 5 having an orifice 5a between the two vacuum chamber 8,9. A rotating disk 7 having an aperture 7a is preferably provided adjacent the thin plate 5. The disk 7 may be rotated so as to vary the area of the effective gas flow aperture between the two vacuum chambers 8,9.

(18) The linear ion trap 10 may be used to accumulate ions whilst the orifice 5a is occluded by the disk 7 and may then be arranged to pulse ions through the orifice 5a once the disk 7 is moved or rotated to align the aperture 7a in the disk 7 with the orifice 5a in the thin plate 5. Advantageously, the gas flow is preferably reduced and the number of ions and hence the sensitivity of the instrument is preferably maintained.

(19) Further embodiments are contemplated wherein the preferred device may be used with a pulsed ion source, such as a MALDI ion source. The pulsed release of ions is preferably synchronised with the rotation of the disk 7 and the opening of the orifice 5a. An optical encoder or similar device may be used to accurately locate the position of the disk 7.

(20) It is also contemplated that instead of continuous rotation of the disk, the opening through the orifice 5a may be temporarily set to a fixed open or closed state, for example, whilst the instrument is not being used.

(21) The present invention is not limited to a rotating disk occlusion member. Other embodiments are contemplated wherein a linear element may be moved vertically and/or horizontally in front of the orifice 5a.

(22) In alternative embodiments, the opening may comprise an iris or other mechanical device or assembly which when operated alters the physical dimension of the opening. Alternatively, the opening may comprise a plastic/elastic tube which is squashed or otherwise deformed to vary the area of the opening.

(23) It is also contemplated that the opening of the aperture 5a may be synchronised with a downstream ion trap. For example, the opening 5a may only be opened for a defined fill-time to fill the downstream ion trap with either a predetermined number of ions or for a predetermined length of time.

(24) The preferred embodiment may also be used with collision/gas cells or with ion mobility spectrometers to limit the gas flow.

(25) Although the present invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as set forth in the accompanying claims.