GAS VALVES FOR ION GUIDES

Abstract

An ion optical arrangement (1) for use in a mass spectrometer comprises electrodes (11) defining an ion optical path, a housing (18) for accommodating the electrodes, a voltage source for providing voltages to the electrodes to produce electric fields, and a valve for allowing gas to enter and/or leave the housing. The valve comprises an electrostatic mechanism and/or a pneumatic mechanism. The electrostatic mechanism may comprise a flexible foil (30, 31) configured for covering at least one opening (16) in the ion optical arrangement when a first voltage is applied and being spaced apart from the at least one opening when a second voltage is applied. The pneumatic mechanism may comprise a Bourdon tube.

Claims

1. An ion optical arrangement for use in a mass spectrometer, comprising: electrodes defining an ion optical path, a housing for accommodating the electrodes, a voltage source for providing voltages to the electrodes to produce electric fields, and a valve for allowing gas to enter and/or leave the housing, wherein the valve comprises an electrostatic mechanism.

2. The ion optical arrangement according to claim 1, wherein the electrostatic mechanism comprises a flexible foil configured for covering at least one opening in the ion optical arrangement when a first voltage is applied and being spaced apart from the at least one opening when a second voltage is applied.

3. The ion optical arrangement according to claim 2, wherein the flexible foil comprises at least one insulating layer and at least one conducting layer.

4. The ion optical arrangement according to claim 2, wherein the flexible foil is arranged in a spacing between the housing and a support element.

5. The ion optical arrangement according to claim 1, further comprising a pump for pressurizing the ion optical arrangement.

6. An electrostatic valve for use in an ion optical arrangement, wherein the electrostatic valve comprises a flexible foil configured for covering at least one opening in the ion optical arrangement when a first voltage is applied and being spaced apart from the at least one opening when a second voltage is applied.

7. An ion optical arrangement for use in a mass spectrometer comprising: electrodes defining an ion optical path, a housing for accommodating the electrodes, a voltage source for providing voltages to the electrodes to produce electric fields, and a valve for allowing gas to enter and/or leave the housing, wherein the valve comprises a pneumatic mechanism.

8. The ion optical arrangement according to claim 7, wherein the pneumatic mechanism comprises a Bourbon tube.

9. The ion optical arrangement according to claim 8, wherein the Bourdon tube is arranged for opening the housing when inflated and closing the housing when deflated.

10. The ion optical arrangement according to claim 9, wherein the housing comprises a hinged flap which is capable of closing off an opening in the housing, and wherein the hinged flap is operated by the Bourdon tube.

11. The ion optical arrangement according to claim 7, further comprising a pump for pressurizing the ion optical arrangement.

12. The ion optical arrangement according to claim 1, which is a collision cell or a collision/reaction cell.

13. A pneumatic valve for use in an ion optical arrangement, comprising a hinged flap arranged for opening and/or closing at least one opening in the ion optical arrangement, and a Bourbon tube arranged to operate the flap.

14. A mass spectrometer comprising an ion optical arrangement according to claim 1.

15. The mass spectrometer according to claim 13, further comprising at least one ion source, such as an inductively coupled plasma ion source, and at least one detector arrangement, such as a multi-collector detector arrangement, and preferably also a mass filter.

16. The ion optical arrangement according to claim 7, which is a collision cell or a collision/reaction cell.

17. A mass spectrometer comprising an ion optical arrangement according to claim 7.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] FIG. 1 schematically shows a multipole collision/reaction cell in which the invention may be utilized.

[0040] FIGS. 2A-2C schematically show an embodiment of an electrostatic pressure release mechanism which may be used with the collision/reaction cell of FIG. 1 or with another ion optical arrangement.

[0041] FIG. 3 schematically shows an ion optical arrangement with an electrostatic valve mechanism according to the invention.

[0042] FIGS. 4A & 4B schematically show an embodiment of a pneumatic pressure release mechanism which may be used with the collision/reaction cell of FIG. 1 or with another ion optical arrangement.

[0043] FIG. 5 schematically shows a mass spectrometer comprising an ion optical arrangement in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] As mentioned above, it is an object of the present invention to allow an ion optical arrangement, such as a collision/reaction cell or a mass filter, to quickly switch between a pressurized state and a depressurized or vacuum state, or between a high pressure state and a low pressure state. Such an ion optical arrangement may also be referred to as switchable ion guide.

[0045] The pressurized state may for example be a state in which a collision gas is used, which may be a state in which the ions have a relatively low energy. The depressurized state may be a state in which a collision gas is not desired, which may be a state in which the ions have a relatively high energy.

[0046] When operating an ion optical arrangement, such as a collision cell, in a pressurized mode and in an evacuated (that is, non-pressurized) mode, it is typically required that the ion optical arrangement can be pressurized and depressurized rapidly. In particular, a pressure release mechanism is desired that is fast and effective.

[0047] FIG. 1 schematically shows an ion optical arrangement in which the invention may be applied. The collision cell 1 is shown to comprise a housing 18 in which a multipole arrangement is accommodated. In the example shown, the multipole arrangement is a hexapole arrangement comprising six elongate poles or rods 11 which constitute electrodes. The multipole arrangement has an axis of symmetry which is the ion optical axis. A radio frequency (RF) voltage may be fed to opposite pairs of poles 11 to produce an RF electric field. Ions can enter the collision cell through an entrance aperture 13 and leave the collision cell through an exit aperture 15. The RF field produced by the multipole arrangement focuses the ions on the longitudinal axis of the arrangement. This is particularly relevant when a collision gas is present in the collision cell, as collisions may cause the ions to deviate from their path.

[0048] The invention provides valve mechanisms which are particularly suitable for use in a collision cell or other ion guide having a pressurized and an evacuated operation mode.

[0049] FIG. 2A schematically shows an electrostatic valve mechanism which may be used in a collision cell, for example. The exemplary collision cell 1 is shown to comprise a housing 18 in which rods 11 are accommodated. An ion beam IB can pass through the collision cell 1, through openings in the front plate 12 and back plate 14 respectively. In the embodiment shown, part of the wall of the housing 18 is provided with through holes 16 which can be closed off by a movable foil. This foil is located in a spacing between the housing 18 and a support element 19, which is here constituted by a plate. Both the housing 18 and the plate 19 contain electrically conductive material and may both be made of metal, or at least contain a metal layer or other conductive layer. The plate 19, which extends substantially parallel to the housing 18, may be flat but may alternatively be curved to accommodate any curvature of the housing 18.

[0050] In the embodiment shown, the foil comprises two layers: a conductive layer 30 and an electrically insulating layer 31. A further electrically insulating layer 32 is attached to the plate 19. In an alternative embodiment, the foil consists of a single layer: the conductive layer 30 only, in which case the insulating layers 31 and 32 are permanently attached to the housing 18 and the plate 19 respectively. In yet an alternative embodiment, the foil consists of three layers: the conductive layer 30 and both insulating layers 31 & 32. Further layers may be added, as long as the foil remains sufficiently flexible. A suitable material for the insulating layers 31 & 32 is Kapton, but other materials, for example other polyimides, may also be used. The conductive layer may be made of copper foil, for example.

[0051] As mentioned above, the flexible foil is located in the spacing between the housing 18 and the plate 19. One edge of the foil may be attached to the housing 18 while the opposite edge may be attached to the plate 19, such that the foil bridges the spacing. By applying DC voltages to the conductive layer, the position of the foils can be changed, as shown in FIG. 9A by the arrows which indicate the possible movement of the substantially S-shaped spacing-bridging portion of the foil.

[0052] Referring to FIG. 2B, the housing 18 will typically be connected to ground (GND). The conductive plate 19 can be connected to a high voltage, indicated by HV in FIG. 9B, thus creating a voltage difference over the spacing between the housing 18 and the plate 19. If the conductive layer 30 is connected to a high voltage, then the foil will be repelled by the plate 19 and attracted by the housing 18. As a consequence, the foil will tend to move towards the housing and the S-shaped spacing bridging part will move to the right (see also FIG. 2A). In other words, electrical forces F.sub.el pulling the foil towards the housing cause a mechanical force F.sub.m to the right in FIG. 2B. The foil will cover the through holes 16 and the interior of the collision cell will be closed off.

[0053] Referring to FIG. 2C, the through holes 16 can be opened by connecting the conductive layer 30 to ground instead of to the high voltage (HV). This will cause the foil to be repelled by the housing 18 and to be attracted by the plate 19, which in turn cause the S-shaped spacing bridging part to move to the left (see also FIG. 2A). In other words, electrical forces F.sub.el pulling the foil towards the plate 19 cause a mechanical force F.sub.m to the left in FIG. 2C. The foil will no longer cover the through holes 16 and the interior of the collision cell will be open to the surrounding atmosphere.

[0054] As the movement of the foil is controlled by voltages, which can be switched extremely quickly, and as the foil can have a very low mass, the movement of the foil can be very quick. Accordingly, the pressure inside the collision cell 1 can be adjusted very rapidly and switching between a pressurized state and an evacuated state can be carried out almost instantly.

[0055] An embodiment of the electrostatic valve is shown in perspective in FIG. 3, together with an ion guide and electric circuitry for operating the electrostatic valve. The ion guide is shown to have a housing 18 with an entrance opening 13 for ions. A flexible foil arrangement is shown to comprise a conductive layer 30, a first insulating layer 31 and a second insulating layer 32. In the embodiment shown, the insulation layers 31 and 32 are permanently attached to the housing 18 and the plate 19 respectively, the conductive layer 30 being the only movable layer. In some embodiments, two or more conductive layers may be used, separated by additional insulating layers.

[0056] In the embodiment shown, the openings 16 in the housing are also present in the first insulating layer 31. In embodiments where the first insulating layer 31 is not attached to the housing but to the conductive layer 30, the openings 16 may not be present in the first insulating layer 31.

[0057] FIG. 3 also schematically shows an electric circuit for operating the electrostatic valve. A voltage source 40 produces a voltage U. A switch 42 allows the conductive layer 30 to connect either to ground (as shown) or to the voltage U. The plate 19 is shown to be permanently connected to the voltage U. If the conductive layer 30 is connected to ground, as shown, it will be attracted to the plate 19 and move towards the plate. Conversely, if the conductive layer 30 is connected to the voltage source 40, then the conductive layer 30 will be repulsed by the plate 19 and move towards the housing 18, thus closing the openings 16.

[0058] FIGS. 4A & 4B show a pneumatic mechanism 20 for adjusting the pumping cross section of an ion guide, for example a collision cell housing 18 having rods 11. The pneumatic valve mechanism 20 is shown to comprise a door or flap 21 which is connected via a hinge 22 to the housing 18 of the collision cell 1. The flap 21 can be operated by an actuator 23 of which one end is connected to the flap 21 and the other end is connected to a support element 24 attached to the housing 18.

[0059] The actuator 23 shown in FIGS. 4A & 4B is a Bourdon tube. A Bourdon tube comprises a bent tube. The bending radius of the bent tube can be decreased if the pressure difference between the inner part and the outer part of tube increases. To this end, a gas tube 25, which is also connected to the support element 24, is connected with the actuator 23. In the embodiment shown, the gas flows from the gas tube 25 through a channel in the support element 24 into the actuator 23 when the gas pressure in the gas tube 25 is higher than the gas pressure surrounding the actuator 23. By letting gas flow into the actuator, its bending radius decreases (the actuator straightens) and the flap is opened. Conversely, the gas flows from the actuator 23 through the support element 24 into the gas tube 25 when the gas pressure in the gas tube 25 is lower than in the actuator 23. By letting gas flow out of the actuator, its bending radius increases (the actuator curves) and the flap is closed.

[0060] Thus, by providing a pressure difference between the gas tube 25 and the air (or other gas) outside the actuator 23, the flap can be quickly opened or closed, thus allowing the gas pressure in the interior of the collision cell 1 to quickly assume the gas pressure on its outside.

[0061] It is noted that the collision cell 1 may be accommodated in a near-vacuum environment, while the gas tube may be connected with an environment under atmospheric pressure. The gas used for inflating the inflatable actuator may be air. As the interior volume of the actuator 23 and the gas tube 25 may be small, only a small amount of air or other gas is needed to inflate the actuator. This air or other gas may be provided by a gas reservoir or by a pump. Thus, a small pump or valve can be sufficient to indirectly operate the relatively large flap.

[0062] By using a Bourdon tube or similar actuator, a fast and effective pressure regulation of a collision cell or other ion guide can be achieved.

[0063] The exemplary mass spectrometer 10 schematically shown in FIG. 5 comprises a multipole cell 1, which can be a collision cell as described above but which can be replaced by an ion guide without a multipole arrangement. The mass spectrometer 10 may further comprise a plasma source 1, such as an ICP (inductively coupled plasma) source for generating an ion beam IB1. The mass spectrometer may further comprise a mass filter 3, such as a magnetic sector mass filter. In the magnetic sector mass filter, the ion beam 1131 is separated into partial beams IB2 having different m/z (mass versus charge) ratios, which partial beams can be detected by the detector assembly 4, which may be a multiple detector assembly. The mass spectrometer 10 may further comprise a pump for lowering the gas pressure in the collision cell 1, a valve associated with the pump, a voltage source 5 for supplying DC and AC (RF) voltages to the collision cell 1, and a controller for controlling the various components of the mass spectrometer 10. The voltage source 5 may correspond with the voltage source 40 in FIG. 3. The valve may comprise a foil-based valve and/or a Bourdon tube-based valve as described above.

[0064] Aspects of the invention comprise: [0065] a) An ion guide, such as a multipole collision cell, which can be rapidly switched between a first operation mode, in which a collision gas and/or reaction gas is present, and a second operation mode, in which no gas is used. [0066] b) Mechanisms for allowing a rapid switch between the first operation mode and the second operation mode.
These aspects of the invention may be used in isolation or in combination.

[0067] Although the invention has been described above mainly with reference to an ion optical arrangement comprising a multipole, such as a hexapole, the invention is not so limited and may also be utilized in other types of ion guides.

[0068] It will therefore be understood by those skilled in the art that the invention is not limited to the embodiments shown and that many additions and/or modifications can be made without departing from the scope of the invention as defined in the appending claims.