Ion optic device

Abstract

An ion optic device comprising a plurality of stacked electrodes 201 arranged on a support member, an electrically insulating sleeve 206 extending through apertures in the electrodes; and a fastener s

Description

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority from and the benefit of United Kingdom patent application No. 2408406.3 filed on 12 June 2024. The entire contents of this application are incorporated herein by reference. FIELD OF THE INVENTION The present invention relates generally to an ion optic device and a mass and / or mobility spectrometer comprising the ion optic device. BACKGROUND Ion optic devices formed from a plurality of stacked electrodes are known. However, it can be relatively difficult to mount together the electrodes of such devices so that they are accurately aligned. SUMMARY According to an aspect of the present invention, there is provided an ion optic device comprising: a plurality of stacked electrodes arranged on a support member; an electrically insulating sleeve extending through apertures in the electrodes; and a screw passing through the sleeve and into the support member so as to clamp the electrodes to the support member. The electrodes may be spaced apart by electrically insulating spacers located between adjacent pairs of electrodes. The spacers may be positioned between planar portions or surfaces of the electrodes. The spacers may be aligned along a common axis. The electrically insulating sleeve may extend through the spacers. That is, the spacers may comprise apertures and the electrically insulating sleeve may extend through the apertures of the spacers. The screw may be electrically conductive, and the sleeve may be configured to electrically insulate the screw from the plurality of electrodes. The electrically insulating sleeve may be tubular. The electrically insulating sleeve may be rigid. An outer diameter of the sleeve may substantially match an inner diameter of the apertures through which it passes such that the electrodes and / or spacers cannot move radially relative to a longitudinal axis through the sleeve. The screw may pass through the sleeve from a first end of the plurality of electrodes to an opposite, second end of the plurality of electrodes. The screw may comprise a first end portion configured to protrude from the second, opposite end of the plurality of electrodes and screw into the support member. The screw may comprise a head portion at a second end that clamps the plurality of electrodes to the support member when the screw is screwed into the support member. The sleeve may protrude from the second, opposite end of the plurality of electrodes and the protruding portion may be received in the support member. The device may further comprise a collar surrounding the screw and arranged between the head portion of the screw and the first end of the plurality of electrodes. The collar may be made of an electrical insulator. The collar may comprise an annular member having an aperture through which the screw passes. The sleeve may protrude from the first end of the plurality of electrodes and the collar may mount around a circumference of the protruding portion of the sleeve. The sleeve may protrude from the first end of the plurality of electrodes so as to space the head portion of the screw from the first end of the plurality of electrodes. The ion optic device may comprise a plurality of electrically insulating sleeves extending through the apertures in the electrodes and a plurality of screws, each screw passing through one of the sleeves and into the support member so as to clamp the electrodes to the support member. The apertures may be located at corners of the plurality of electrodes. Alternatively, the apertures may be located along a perimeter of the plurality of electrodes. The ion optic device may comprise one or more voltage supplies for applying AC and / or DC voltages to the electrodes. At least some of the electrodes may have openings therethrough for ions to pass through. The ion optic device may be an orthogonal accelerator configured to receive ions along one axis between two of the plurality of electrodes and having one or more voltage supplies connected to the electrodes that are configured to apply a voltage pulse to one or more of the electrodes so as to push the ions in a direction that is orthogonal to said axis and through the openings in the electrodes. In an embodiment, there is provided a mass and / or ion mobility spectrometer comprising the ion optic device described above. According to another aspect of the present invention, there is provided a method of forming an ion optic device, the method comprising: extending an electrically insulating sleeve through apertures in a plurality of stacked electrodes; and passing a screw through the sleeve and into a support member so as to clamp the electrodes to the support member. The method may comprise spacing apart the electrodes by locating electrically insulating spacers between adjacent pairs of electrodes. The method may comprise positioning the spacers between planar portions or surfaces of the electrodes. The method may comprise aligning the spacers along a common axis. The method may comprise extending the electrically insulating sleeve through the spacers. That is, the spacers may comprise apertures and the method may comprise extending the electrically insulating sleeve through the apertures of the spacers. The screw may be electrically conductive, and the method may comprise electrically insulating the screw from the plurality of electrodes using the sleeve. The electrically insulating sleeve may be tubular. The electrically insulating sleeve may be rigid. An outer diameter of the sleeve may substantially match an inner diameter of the apertures through which it passes such that the electrodes and / or spacers cannot move radially relative to a longitudinal axis through the sleeve. The method may comprise passing the screw through the sleeve from a first end of the plurality of electrodes to an opposite, second end of the plurality of electrodes. The method may comprise protruding a first end portion of the screw from the second, opposite end of the plurality of electrodes and screwing the first end portion of the screw into the support member. The method may comprise clamping the plurality of electrodes to the support member when the screw is screwed into the support member using a head portion at a second end of the screw. The method may comprise protruding the sleeve from the second, opposite end of the plurality of electrodes and receiving the protruding portion in the support member. The method may comprise surrounding the screw with a collar arranged between the head portion of the screw and the first end of the plurality of electrodes. The collar may be made of an electrical insulator. The collar may comprise an annular member having an aperture through which the screw passes. The method may comprise protruding the sleeve from the first end of the plurality of electrodes and mounting the collar around a circumference of the protruding portion of the sleeve. The method may comprise protruding the sleeve from the first end of the plurality of electrodes so as to space the head portion of the screw from the first end of the plurality of electrodes. The method may comprise extending a plurality of electrically insulating sleeves through apertures in the electrodes and passing a plurality of screws through the sleeves, each screw passing through one of the sleeves and into the support member so as to clamp the electrodes to the support member. The apertures may be located at corners of the plurality of electrodes. Alternatively, the apertures may be located along a perimeter of the plurality of electrodes. The method may comprise applying one or more AC and / or DC voltages to the electrodes. At least some of the electrodes may have openings therethrough for ions to pass through. The ion optic device may be an orthogonal accelerator and the method may comprise receiving ions along one axis between two of the plurality of electrodes and applying a voltage pulse to one or more of the electrodes so as to push the ions in a direction that is orthogonal to said axis and through the openings in the electrodes. According to another aspect of the present invention, there is provided an ion optic device comprising: a plurality of stacked electrodes; an electrically insulating sleeve extending through apertures in the electrodes; and a fastener extending through the sleeve and configured to clamp the plurality of electrodes together. The ion optic device may comprise any of the features described above, except that the fastener is not limited to a screw. According to another aspect of the present invention, there is provided a method of forming an ion optic device comprising: extending an electrically insulating sleeve through apertures in a plurality of stacked electrodes; and extending a fastener through the sleeve so as to clamp the plurality of electrodes together. The method may comprise any of the features described above, except that the fastener is not limited to a screw. BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which: Fig. 1 illustrates a schematic of a mass spectrometer according to an embodiment of the present invention; and Fig. 2 illustrates a schematic of an orthogonal accelerator according to an embodiment of the present invention. DETAILED DESCRIPTION Fig. 1 illustrates a schematic of a mass spectrometer 100 according to an embodiment of the present invention. The mass spectrometer 100 comprises an ion source 101 configured to generate analyte ions, an ion guide 102 located in a first vacuum chamber, an ion transfer lens 103 located in a second vacuum chamber, and an orthogonal acceleration Time of Flight (“TOF”) mass analyser 107 located in a third vacuum chamber. As illustrated in Fig. 1, the TOF mass analyser 107 comprises an orthogonal accelerator 104 and an ion detector 106 separated by a time of flight region. The orthogonal accelerator 104 comprises one or more pusher electrode(s) and / or one or more puller electrode(s). One or more reflectrons 105 (i.e. one or more ion mirrors) are provided intermediate the orthogonal accelerator 104 and the ion detector 106, and the ion detector 106 is arranged to detect ions reflected by the one or more reflectrons 105. In use, gas is pumped out of the vacuum chambers by one or more vacuum pumps so as to reduce the pressure inside them. The third vacuum chamber may be maintained at a lower pressure than the second vacuum chamber and the second vacuum chamber may be maintained at a lower pressure than the first vacuum chamber. The first vacuum chamber may be maintained at lower pressure than ambient. Ions are generated by the ion source 101 and pass into the first vacuum chamber. The ions are guided through the first vacuum chamber by the ion guide 102 and into the second vacuum chamber. The ions pass through the ion transfer lens 103 in the second vacuum chamber and into the third vacuum chamber. The ions then arrive at the orthogonal accelerator 104 of the TOF mass analyser 107. At the orthogonal accelerator 104, the ions pass between two of the electrodes of the orthogonal accelerator 104. A pulsed voltage is applied to one or both of the electrodes in order to generate a potential difference between the electrodes that causes the ions to be accelerated orthogonally as an ion packet. The electrodes of the orthogonal accelerator 104 towards which the ion packet is accelerated each comprise an aperture so that the ion packet can pass through the electrodes and out of the orthogonal accelerator 104. These electrodes have voltages applied to them so as to maintain an electric field along the ion path that spatially focuses the ions. The packet of ions is pushed into the time of flight region by the orthogonal accelerator 104 towards the reflectron 105. Voltages are then applied to the reflectron in order to generate an electric field that reflects the packet of ions back through the time of flight region and onto the ion detector 106. The ions are then mass analysed by the TOF mass analyser 107 in the known manner, i.e. by determining the mass to charge ratios of the ions based on their flight time from orthogonal accelerator 104 to the ion detector 106. The mass spectrometer 100 shown in Fig. 1 is illustrative and may comprise different or additional ion optical devices to those shown, and / or a different number of vacuum chambers. For example, according to various embodiments the mass spectrometer 100 may additionally comprise one or more ion separation devices, one or more ion traps, one or more collision, fragmentation or reaction cells, or one or more mass filters. The present invention relates to an ion optic device formed from a plurality of stacked electrodes, such as an orthogonal accelerator for a TOF mass analyser. Fig. 2 illustrates a schematic of an orthogonal accelerator 200 according to an embodiment of the present invention. The orthogonal accelerator 200 comprises a plurality of stacked electrodes 201, i.e. electrodes that are spaced apart along an axis of the orthogonal accelerator 200. The electrodes 201 are spaced apart by electrically insulating spacers 208 located between each adjacent pair of the electrodes 201. The spacers 208 are made from an electrical insulator such that the different electrodes 201 of the orthogonal accelerator 200 can be maintained at different voltages. The electrodes 201 may be planar and may be aligned, with planar surfaces adjacent and parallel to each other. It is also contemplated that the electrodes may not be planar but may instead comprise planar portions where the spacers 208 are located. Although illustrated with a rectangular shape, the electrodes 201 may comprise any suitable shape. The stack of electrodes 201 may comprise electrodes of different thicknesses or electrodes having the same thickness. Each electrode 201 comprises a plurality of apertures located at its corners, where each of the apertures is aligned with corresponding apertures of the adjacent electrodes 201, i.e. along a common axis. Although the apertures are shown as being located at the corners of the electrodes 201, they may be located at other locations, such as other locations along the perimeter of the electrodes 201. The apertures in each set of apertures that are aligned are configured to receive a sleeve 206 therethrough. The sleeve 206 is formed from an electrical insulator such as a ceramic, and may be tubular. The sleeve 206 extends through the set of apertures in the electrodes and may have an external diameter that substantially matches the internal diameter of each of the apertures that it passes through, so as to prevent the electrodes moving radially relative to the axis of the sleeve. The sleeve 206 may be rigid. A screw 202 is passed through the sleeve 206 in order to clamp the electrodes 201 together. More specifically, the screw 202 is configured to pass through the sleeve from a first end of the stack of electrodes to the opposite, second end of the stack of electrodes. A first end portion of the screw 202 protrudes from the second end of the stack of electrodes 201 and has a screw thread thereon. The orthogonal accelerator has a support member on which the stack of electrodes is mounted. This support member has a recess therein for receiving the first end portion of the screw 202, and the interior of the recess is screw threaded in a complementary manner to the screw thread on the screw 202. As such, the screw is screwed into the support member. The second end of the screw 202 may comprise a head portion 204 that is enlarged in the radial direction relative to the rest of the screw, for clamping the stack of electrodes to the support member when the screw is screwed into the support member. The end of the sleeve 206 may also be received in the recess. In these embodiments the recess may have a first length that extends from the surface of the support member that the electrodes are stacked on and which has a relatively large diameter, and a second length further from the surface of the support member and that has a smaller diameter. The diameter of the first length may substantially match the outer diameter of the sleeve 206. The diameter of the second length is smaller than the diameter of the first length, and includes the complementary screw threads into which the screw is screwed. As the sleeve is made of an electrical insulator, the screw that passes therethrough is able to be formed from any material, including an electrically conductive material, without the screw contacting the majority of the electrodes. In embodiments in which the screw is electrically conductive, it may be desired to electrically insulate the screw head from the electrode at the first end of the electrode stack. This may be done by providing a collar 207 that is formed from an electrical insulator between the screw head and the electrode at the first end of the electrode stack. The collar may be an annular member having an aperture through which the screw passes. It will be appreciated that the collar may or may not extend around the full circumference of the screw, provided that it spaces the screw head from the electrode at the first end of the electrode stack when the screw is screwed into the recess in the supporting member so as to clamp the stack of electrodes to the supporting member. Other embodiments are contemplated in which the collar is not provided and instead the sleeve has a length such that when the screw is screwed into the recess to clamp the stack of electrodes to the supporting member, the end of the sleeve protrudes from the first end of the stack of electrodes so as to space the screw head from the electrode at the first end of the stack. Alternatively, the screw may be an electrically insulating material. The provision of the electrically insulating sleeve 206, and optionally the electrically insulating collar 207, allows the screw 202 to be formed from electrically conductive materials. For example, the screw may be an electrically conductive metal such as steel, which may provide relatively high strength. Additionally, it has been recognised that a conventional screw may be used and the sleeve 206 may be formed with an outer diameter having a relatively high tolerance, improving alignment of the electrodes 201. The spacers 208 may be surround the sleeve 206. That is, the sleeve 206 (and screw 202) may extend through the spacers 208 and electrodes 201, alternately. The spacers 208 may be aligned along the same axis as the screw 202 and sleeve 206. It will be appreciated that passing the sleeve 206 and screw 202 through the spacers 208 helps prevent the bending of the electrodes 201 that would otherwise occur if the screw 202 and spacers 208 were provided on different axes. Each of the sleeve 206, spacers 208 and collar 207 may be constructed from any suitable electrically insulating material, for example a ceramic or plastic, such as polyether ether ketone (“PEEK”). Each of the electrodes 201, except for the pusher electrode, comprises a central aperture 209 so as to form a passage through these electrodes for ions to pass through when they are orthogonally accelerated. During operation of the orthogonal accelerator 200, ions may be introduced into the orthogonal accelerator 200 between two of the electrodes 201, e.g. as has been described in relation to Fig. 1. As the ions pass between the electrodes, one or more voltages may then be applied to the electrodes 201 so as to pulse a packet of the ions orthogonally such that the packet of ions passes along the passage formed by the apertures 209 in the electrodes and out of the orthogonal accelerator 200. Although the present invention has been described with reference to various 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. For example, although, the electrodes 201 of the orthogonal accelerator 200 are illustrated as having four screws 202 (one at each corner), the electrodes may comprise one, two, three, four, or more screws. It is also not necessary to use a screw 202 to secure the electrodes to the support member 203. In particular, in alternative embodiments, the screw is replaced by a rod that extends from the support member and the sleeve 206, spacers 208 and electrodes 201 slide onto the rod. The electrodes may then be clamped against the support member 203 by various means. For example, a nut may be screwed onto the free end of the rod so as to clamp the electrodes in place, 5 or a resilient biasing member may be arranged between the free end of the rod and the electrode stack so as to urge the electrodes towards the support member. Alternatively, other urging or locking means may be provided, such as a cam member that is turned to a position in which it holds the electrode stack against the support member. 10 The orthogonal accelerator 200 is an example of an ion optic device of the present invention. However, the ion optic device of the present invention is not limited to orthogonal accelerators 200. It will be appreciated that the present invention can be applied to any ion optic device that comprises a plurality of stacked electrodes 201. For example, the ion optic device may comprise an ion 15 guide, a linear accelerator, or a reflectron. Accordingly, it will be appreciated that the ion optic device is not limited to use in a Time of Flight mass analyser, and may be used to process ions in other devices, such as an ion mobility spectrometer.

Claims

1. An ion optic device comprising:a plurality of stacked electrodes arranged on a support member;an electrically insulating sleeve extending through apertures in the electrodes; anda screw passing through the sleeve and into the support member so as to clamp the electrodes to the support member.

2. The device of claim 1, wherein the electrodes are spaced apart by electrically insulating spacers located between adjacent pairs of electrodes.

3. The device of claim 2, wherein the electrically insulating sleeve extends through the spacers.

4. The device of claim 1, 2 or 3, wherein the screw is electrically conductive, and wherein the sleeve is configured to electrically insulate the screw from the plurality of electrodes.

5. The device of any preceding claim, wherein the electrically insulating sleeve is tubular.

6. The device of any preceding claim, wherein an outer diameter of the sleeve substantially matches an inner diameter of the apertures through which it passes such that the electrodes cannot move radially relative to a longitudinal axis through the sleeve.

7. The device of any preceding claim, wherein the screw passes through the sleeve from a first end of the plurality of electrodes to an opposite, second end of the plurality of electrodes;wherein the screw comprises a first end portion configured to protrude from the second, opposite end of the plurality of electrodes and screw into the support member; andwherein the screw comprises a head portion at a second end that clamps the plurality of electrodes to the support member when the screw is screwed into the support member.

8. The device of claim 7, further comprising a collar surrounding the screw and arranged between the head portion of the screw and the first end of the plurality of electrodes.

9. The device of claim 8, wherein the collar is made of an electrical insulator.

10. The device of claim 8 or 9, wherein the collar comprises an annular memberhaving an aperture through which the screw passes.

11. The device of claim 8, 9 or 10, wherein the sleeve protrudes from the first end of the plurality of electrodes and the collar mounts around a circumference of the protruding portion of the sleeve.

12. The device of any one of claims 7-10, wherein the sleeve protrudes from the first end of the plurality of electrodes so as to space the head portion of the screw from the first end of the plurality of electrodes.

13. The device of any preceding claim, wherein the ion optic device comprises a plurality of electrically insulating sleeves extending through the apertures in the electrodes and a plurality of screws, each screw passing through one of the sleeves and into the support member so as to clamp the electrodes to the support member.

14. The device of any preceding claim, wherein the apertures are located at corners of the plurality of electrodes.

15. The device of any preceding claim, comprising one or more voltage supplies for applying AC and / or DC voltages to said electrodes.

16. The device of any preceding claim, wherein at least some of the electrodes have openings therethrough for ions to pass through.

17. The device of claim 16, wherein the ion optic device is an orthogonal accelerator configured to receive ions along one axis between two of the plurality of electrodes and having one or more voltage supplies connected to the electrodes that are configured to apply a voltage pulse to one or more of the electrodes so as to push the ions in a direction that is orthogonal to said axis and through the openings in the electrodes.

18. An ion optic device comprising: a plurality of stacked electrodes;an electrically insulating sleeve extending through apertures in the electrodes; anda fastener extending through the sleeve and configured to clamp the plurality of electrodes together.

519. A mass and / or ion mobility spectrometer comprising the ion optic device of any preceding claim.

20. A method of forming an ion optic device according to any one of claims 110 18, comprising:extending an electrically insulating sleeve through apertures in a plurality of electrodes; andpassing a screw or other fastener through the sleeve so as to clamp the electrodes to a support member.

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