Ion guide

Abstract

An ion guide is disclosed comprising a first array of electrodes and a second array of electrodes and one or more apertures or ion exit regions. The first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions. The ion guide comprises a first device arranged and adapted to apply an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays, and a second device arranged and adapted to apply one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a second (r) direction towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions.

Claims

1. An ion guide comprising: a first array of electrodes and a second array of electrodes; one or more apertures or ion exit regions; wherein said first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions; a first device arranged and adapted to apply an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays; a second device arranged and adapted to apply one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a radial (r) direction relative to an axis about which said first and/or second plurality of arcuate electrodes are arranged towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions, and such that ions within said ion guide are caused to exit said ion guide via said one or more apertures or ion exit regions in a non-mass-selective manner; and one or more ion entrance regions arranged and adapted such that ions can enter said ion guide via said one or more ion entrance regions in said first (z) and/or said radial (r) direction, and at some or all angular (θ) displacements around the axis about which said first plurality of arcuate electrodes and/or said second plurality of arcuate electrodes are arranged, wherein said one or more ion entrance regions are arranged and adapted such that ions can enter said ion guide at at least 90% of the angular displacements; wherein the one or more ion entrance regions comprise an annular region located at or close to the circumference of said first array of electrodes and/or said second array of electrodes; wherein said second device is arranged and adapted: to apply different DC voltages to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a DC voltage gradient that urges ions within said ion guide in said radial (r) direction to said one or more apertures or ion exit regions; and/or to successively apply a DC voltage to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a travelling DC potential barrier that travels in said radial (r) direction towards said one or more apertures or ion exit regions so as to urge ions within said ion guide to said one or more apertures or ion exit regions; and to apply said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions; and wherein said ion guide is arranged and adapted such that said one or more DC voltages cause said ions to freely migrate in said radial (r) direction, without being trapped in said radial (r) direction; wherein said ion guide is further arranged and adapted such that ions appearing at any point on the circumference of said one or more ion entrance regions at a given time will be transported and focused to said one or more apertures or ion exit regions; and wherein said ion guide is configured to receive annular distributed ions at the one or more ion entrance regions from a cylindrical ion guide or annular trap, and to collimate said annular distributed ions to an ion beam by said one or more DC voltages transporting and focusing said annular distributed ions to said one or more apertures or ion exit regions without said ions being trapped in said radial (r) direction.

2. An ion guide as claimed in claim 1, wherein: said one or more apertures or ion exit regions are arranged within said first array and/or within said second array; and said first plurality of arcuate electrodes are arranged concentrically around said one or more apertures or ion exit regions and/or wherein said second plurality of arcuate electrodes are arranged concentrically around said one or more apertures or ion exit regions.

3. An ion guide as claimed in claim 2, wherein: said first array of electrodes comprises a first plurality of continuous electrodes, wherein each continuous electrode is arranged concentrically around said one or more apertures or ion exit regions, and/or said second array of electrodes comprises a second plurality of continuous electrodes, wherein each continuous electrode is arranged concentrically around said one or more apertures or ion exit regions; and/or said first array of electrodes comprises a first plurality of groups of electrodes, wherein each group of electrodes is arranged concentrically around said one or more apertures or ion exit regions so as to substantially surround said one or more apertures or ion exit regions and/or said second array of electrodes comprises a second plurality of groups of electrodes wherein each group of electrodes is arranged concentrically around said one or more apertures or ion exit regions so as to substantially surround said one or more apertures or ion exit regions.

4. An ion guide as claimed in claim 3, wherein: said first array of electrodes comprises a first plurality of closed loop, ring, circular or oval electrodes arranged concentrically around said one or more apertures or ion exit regions and/or said second plurality of electrodes comprises a second plurality of closed loop, ring, circular or oval electrodes arranged concentrically around said one or more apertures or ion exit regions; and/or said first array of electrodes comprises a first plurality of rotationally symmetric groups of electrodes wherein each of said groups of electrodes is arranged concentrically around said one or more apertures or ion exit regions and/or said second plurality of electrodes comprises a second plurality of rotationally symmetric groups of electrodes wherein each of said groups of electrodes is arranged concentrically around said one or more apertures or ion exit regions.

5. An ion guide as claimed in claim 1, wherein: said first and second arrays of electrodes are arranged at different displacements in said first (z) direction; and/or said first (z) direction is substantially orthogonal to said radial (r) direction.

6. An ion guide as claimed in claim 1, wherein: said first array of electrodes is arranged in a first plane and/or said second array of electrodes is arranged in a second plane; or said first array of electrodes is arranged in a non-planar configuration and/or said second array of electrodes is arranged in a non-planar configuration.

7. An ion guide as claimed in claim 1, wherein said second device is arranged and adapted to apply said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction to said one or more apertures or ion exit regions, such that ions, that are at any angular (θ) displacement around an axis about which said first and/or said second plurality of arcuate electrodes are arranged, within said ion guide are caused to migrate to said one or more apertures or ion exit regions.

8. An ion guide as claimed in claim 1, wherein said second device is arranged and adapted to apply said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction to said one or more apertures or ion exit regions such that ions within said ion guide at some or all radial (r) displacements, relative to the axis about which said first and/or said second plurality of arcuate electrodes are arranged, are caused to migrate to said one or more apertures or ion exit regions.

9. An ion guide as claimed in claim 1, wherein: said ion guide further comprises one or more extraction lenses or electrode arrangements arranged adjacent to said one or more apertures or ion exit regions, said one or more extraction lenses or electrode arrangements arranged and adapted to cause ions within said ion guide to exit said ion guide via said one or more apertures or ion exit regions.

10. An ion guide as claimed in claim 1, wherein said ion guide is arranged and adapted such that ions are caused to exit said ion guide via said one or more apertures or ion exit regions in said first (z) direction.

11. An ion guide as claimed in claim 1, wherein a buffer gas is provided within said ion guide.

12. A method of guiding ions in an ion guide comprising a first array of electrodes, a second array of electrodes, one or more apertures or ion exit regions, and one or more ion entrance regions, wherein said one or more ion entrance regions comprise an annular region located at or close to the circumference of the first array of electrodes and/or the second array of electrodes, wherein said first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions, the method comprising: applying an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays; and applying one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a radial (r) direction relative to an axis about which said first and/or second plurality of arcuate electrodes are arranged towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions, and such that ions within said ion guide are caused to exit said ion guide via said one or more apertures or ion exit regions in a non-mass-selective manner; and causing ions to enter said ion guide via said one or more ion entrance regions in said first (z) and/or said radial (r) direction, and at some or all angular (θ) displacements around the axis about which said first plurality of arcuate electrodes and/or said second plurality of arcuate electrodes are arranged, wherein said one or more ion entrance regions are arranged and adapted such that ions can enter said ion guide at at least 90% of the angular displacements; wherein applying said one or more DC voltages comprises applying different DC voltages to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a DC voltage gradient that urges ions within said ion guide in said radial (r) direction to said one or more apertures or ion exit regions; and/or wherein applying said one or more DC voltages comprises successively applying a DC voltage to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a travelling DC potential barrier that travels in said radial (r) direction towards said one or more apertures or ion exit regions so as to urge ions within said ion guide to said one or more apertures or ion exit regions; and wherein applying said one or more DC voltages comprises applying said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions; wherein applying said one or more DC voltages comprises applying said one or more DC voltages such that said ions freely migrate in said radial (r) direction, without being trapped in said radial (r) direction; wherein applying said one or more DC voltages comprises applying said one or more DC voltages such that ions appearing at any point on the circumference of said one or more ion entrance regions at a given time will be transported and focused to said one or more apertures or ion exit regions; and wherein the method comprises receiving annular distributed ions at the one or more ion entrance regions from a cylindrical ion guide or an annular trap, and collimating said annular distributed ions to an ion beam by said one or more DC voltages transporting and focusing said annular distributed ions to said one or more apertures or ion exit regions without said ions being trapped in said radial (r) direction.

13. An ion guide comprising: a first array of electrodes and a second array of electrodes; one or more apertures or ion entrance regions; wherein said first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion entrance regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion entrance regions; a first device arranged and adapted to apply an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays; a second device arranged and adapted to apply one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a radial (r) direction relative to an axis about which said first and/or second plurality of arcuate electrodes are arranged away from said one or more apertures or ion entrance regions, such that ions within said ion guide are caused to migrate away from said one or more apertures or ion entrance regions, and such that ions within said ion guide are caused to exit said ion guide in a non-mass-selective manner; and one or more ion exit regions arranged and adapted such that ions can exit said ion guide via said one or more ion exit regions in said first (z) and/or said radial (r) direction, and at some or all angular (θ) displacements around the axis about which said first plurality of arcuate electrodes and/or said second plurality of arcuate electrodes are arranged, wherein said one or more ion exit regions are arranged and adapted such that ions can exit said ion guide at at least 90% of the angular displacements; wherein the one or more ion exit regions comprise an annular region located at or close to the circumference of said first array of electrodes and/or said second array of electrodes; wherein said second device is arranged and adapted: to apply different DC voltages to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a DC voltage gradient that urges ions within said ion guide in said radial (r) direction away from said one or more apertures or ion entrance regions; and/or to successively apply a DC voltage to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a travelling DC potential barrier that travels in said radial (r) direction away from said one or more apertures or ion entrance regions so as to urge ions within said ion guide away from said one or more apertures or ion entrance regions; and to apply said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction away from said one or more apertures or ion entrance regions, such that ions within said ion guide are caused to migrate away from said one or more apertures or ion entrance regions; and wherein said ion guide is arranged and adapted such that said one or more DC voltages cause said ions to freely migrate in said radial (r) direction, without being trapped in said radial (r) direction; wherein said ion guide is further arranged and adapted such that ions appearing at said one or more apertures or ion entrance regions at a given time will be transported away from said one or more apertures or ion entrance regions and will exit said ion guide via said one or more ion exit regions; and wherein said ion guide is configured to receive an ion beam at the one or more apertures or ion entrance regions, and to distribute said ions to an annular volume by said one or more DC voltages transporting said ions to said one or more exit regions without said ions being trapped in said radial (r) direction.

14. An ion guide comprising: a first array of electrodes and a second array of electrodes; one or more apertures or ion exit regions; wherein said first array of electrodes comprises a first plurality of arcuate electrodes arranged in parallel with one another and such that said first plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions and/or wherein said second array of electrodes comprises a second plurality of arcuate electrodes arranged in parallel with one another and such that said second plurality of arcuate electrodes at least partially surround said one or more apertures or ion exit regions; wherein said first plurality of arcuate electrodes are arranged in a sector configuration and/or said second plurality of arcuate electrodes are arranged in a sector configuration; a first device arranged and adapted to apply an AC or RF voltage to said first array of electrodes and to said second array of electrodes so as to confine ions within said ion guide in a first (z) direction that extends in a direction between said first and second arrays; a second device arranged and adapted to apply one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in a radial (r) direction relative to an axis about which said first and/or second plurality of arcuate electrodes are arranged towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions, and such that ions within said ion guide are caused to exit said ion guide via said one or more apertures or ion exit regions in a non-mass- selective manner; and one or more ion entrance regions arranged and adapted such that ions can enter said ion guide via said one or more ion entrance regions in said first (z) and/or said radial (r) direction, and at some or all angular (θ) displacements around the axis about which said first plurality of arcuate electrodes and/or said second plurality of arcuate electrodes are arranged, wherein said one or more ion entrance regions are arranged and adapted such that ions can enter said ion guide at at least 10% of the angular displacements; wherein the one or more ion entrance regions comprise a curved region located at or close to the perimeter of said first array of electrodes and/or said second array of electrodes; wherein said second device is arranged and adapted: to apply different DC voltages to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a DC voltage gradient that urges ions within said ion guide in said radial (r) direction to said one or more apertures or ion exit regions; and/or to successively apply a DC voltage to different electrodes of said first array of electrodes and/or said second array of electrodes so as to create a travelling DC potential barrier that travels in said radial (r) direction towards said one or more apertures or ion exit regions so as to urge ions within said ion guide to said one or more apertures or ion exit regions; and to apply said one or more DC voltages to said first array of electrodes and/or to said second array of electrodes so as to urge ions within said ion guide in said radial (r) direction towards said one or more apertures or ion exit regions, such that ions within said ion guide are caused to migrate to said one or more apertures or ion exit regions; and wherein said ion guide is arranged and adapted such that said one or more DC voltages cause said ions to freely migrate in said radial (r) direction, without being trapped in said radial (r) direction; wherein said ion guide is further arranged and adapted such that ions appearing at any point on the perimeter of said one or more ion entrance regions at a given time will be transported and focused to said one or more apertures or ion exit regions; and wherein said ion guide is configured to receive arcuately distributed ions at the one or more ion entrance regions from an arcuate ion guide or arcuate trap, and to collimate said arcuately distributed ions to an ion beam by said one or more DC voltages transporting and focusing said arcuately distributed ions to said one or more apertures or ion exit regions without said ions being trapped in said radial (r) direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

(2) FIG. 1(a) shows schematically a perspective view of an ion guide in accordance with a first embodiment; FIG. 1(b) shows schematically a perspective view of an ion guide in accordance with a second embodiment; FIG. 1(c) shows a time varying potential generated within the ion guide of the first embodiment; FIG. 1(d) shows a static potential generated within the ion guide of the second embodiment; FIG. 1(e) shows schematically a cross-sectional view of an ion guide in accordance with an embodiment; and FIG. 1(f) shows schematically a cross-sectional view of an ion guide in accordance with an embodiment;

(3) FIG. 2(a) shows schematically a perspective view of an ion guide in accordance with a third embodiment; and FIG. 2(b) shows a time varying potential generated within the ion guide of the third embodiment; and

(4) FIG. 3(a) shows schematically a perspective view of an ion guide in accordance with a fourth embodiment; and FIG. 3(b) shows a time varying potential generated within the ion guide of the fourth embodiment.

(5) FIG. 4(a) shows schematically a perspective view of an ion guide in accordance with a fifth embodiment; and FIG. 4(b) shows a time varying potential generated within the ion guide of the fifth embodiment.

DETAILED DESCRIPTION

(6) An embodiment will now be described.

(7) As shown in FIG. 1, the ion guide may comprise a first planar array of electrodes 1 and a second planar array of electrodes 2. As shown in FIGS. 1(a) and 1(b), the first 1 and second 2 planar arrays of electrodes may comprise first and second pluralities of electrodes, such as first and second pluralities of concentric ring electrodes, respectively. As shown in FIGS. 1(e) and (f), the electrodes may be mounted on electrode supports, which may comprise printed circuit boards 3.

(8) The first and second pluralities of electrodes may be arranged to be parallel to one another (e.g. in the second, radial (r) direction), may be separated by a displacement in a first (z) direction orthogonal to the planes of the electrodes, and may be aligned along the first (z) direction. (The second (r) direction may be the radial direction defined relative to the z-axis depicted in FIGS. 1(a)-(d).)

(9) A buffer gas may be provided within the ion guide, e.g. between the arrays of electrodes. This can be used to collisionally cool ions within the ion guide.

(10) A first ion exit 4 may be arranged in the plane of the first planar array of electrodes, and a second ion exit 5 may be arranged in the plane of the second planar array of electrodes. Each ion exit, may for example, be located at the centre of the first and/or second plurality of electrodes, e.g. at the centre of the concentric ring electrodes. Each ion exit may be provided as an aperture, e.g. in the first or second plurality of electrodes and/or in the electrode support. Each ion exit may comprise, for example, an aperture in the central ring electrode of the plurality of concentric ring electrodes.

(11) One or more ion entrance regions may be provided such that ions can enter the ion guide over a wide range of (e.g. all) angular (θ) displacements. (The angular (θ) displacement may be defined relative to (i.e. around) the z-axis depicted in FIGS. 1(a)-(d), and may be orthogonal to the first (z) direction and the second, radial (r) direction.)

(12) As shown in FIG. 1(e), ions may be arranged to enter the ion guide in a direction parallel to the first and second planes (the radial (r) direction). In this embodiment, ions may be arranged to enter the ion guide at the open ends of the ion guide between the first and second planar arrays of electrodes, i.e. at the perimeter or circumference of the arrays of electrodes. Thus, the ion entrance region 6 may comprise an annular region at the outer region of, and between, the first a second planar arrays of electrodes.

(13) As shown in FIG. 1(f), additionally or alternatively, ions may be arranged to enter the ion guide in a direction orthogonal to the first and second planes, e.g. in the first (z) direction. In this embodiment, the ion entrance region 7 may comprise one or more annular regions arranged in the first and/or second plane, which may be in the outer region of the first and/or second planar array of electrodes.

(14) One or more guard or extraction electrodes 8 may be provided at the ion entrance region(s) to selectively prevent or allow ions to enter the ion guide.

(15) Ions may be confined in the first (z) direction under the influence of pseudo-potential barriers resulting from an AC or RF voltage being applied to the electrodes. Opposite phases of the AC or RF voltage may be applied to adjacent electrodes, e.g. adjacent concentric ring electrodes, of the first and/or second plurality of electrodes. The AC or RF voltage may generate a repulsive effective or pseudo-potential (e.g. a reflective pseudo-potential surface) which may act to prevent ions from striking the electrodes. This confines ions in the first (z) direction.

(16) Ions may also be subjected to a force that urges ions in a direction parallel to the first and/or second plane, and that may be directed towards at least one of the ion exits 4, 5, e.g. inwardly towards an ion exit. The urging force may be directed towards the ion exit in an inward radial (r) direction. The urging force may cause ions to migrate to (i.e. to be transported to) one of the ion exits 4, 5. Ions at most or all angular (θ) displacements and/or at most or all radial (r) displacements within the ion guide may be caused to migrate to one of the ion exits 4, 5.

(17) The direction in which the urging force acts may have (approximate) circular symmetry, e.g. centred on the ion exit, but this need not be the case. The direction in which the urging force acts may have some degree of rotational symmetry, e.g. at least 3-fold rotational symmetry, such that ions at any point within the ion guide (i.e. between the two planar arrays of electrodes) are urged inwardly towards an ion exit.

(18) The urging force may be provided by an electric field, such as a static electric field or a time varying electric field. The static electric field may be provided by applying DC voltages to the first and/or second plurality of electrodes to form a DC voltage gradient that urges ions inwardly towards the ion exit. For example, DC voltages may be applied to the plurality of concentric (ring) electrodes to form a DC voltage gradient that urges ions radially inwards towards the ion exit. FIG. 1(d) illustrates a potential within the ion guide in accordance with this embodiment.

(19) Additionally or alternatively, a time varying electric field may be provided by applying a DC voltage successively to the plurality of electrodes in a direction inwardly towards the ion exit. This creates a potential barrier that travels inwardly towards the ion exit and drives the ions inwardly towards the ion exit. For example, a DC voltage may be applied successively to the plurality of concentric (ring) electrodes in a direction from the outermost (ring) electrode(s) towards the innermost (ring) electrode(s). The travelling potential may be applied such that it repeatedly travels from the outermost electrode(s) to the innermost electrode(s). FIG. 1(c) illustrates a potential within the ion guide in accordance with this embodiment. The travelling potential may be applied such that it travels in the direction shown by the arrows.

(20) Thus, according to an embodiment, ions may be confined in the first (z) direction within the first and second plurality of electrodes (i.e. by the pseudo-potential barriers), while at the same time the ions may be urged toward the one or more ion exits 4, 5, i.e. such that ions are caused to migrate to the one or more ion exits 4, 5. The net effect is to urge or focus ions to a focal point or volume in close proximity with (e.g. above) the one or more ion exits 4, 5.

(21) Ions may be arranged to exit the ion guide via the one or more ion exits 4, 5. Ions may be urged or focused to the focal point adjacent to the one or more ion exits 4, 5, and are urged or forced through the one or more ion exits 4, 5. This may be achieved due to the pseudo-potential, e.g. no pseudo-potential barrier or a minimum in the pseudo-potential barrier is provided at the ion exit, e.g. as a result of the aperture in the central ring electrode. Additionally or alternatively, one or more arrangements of electrodes 9 may be provided at the one or more ion exits, and used to urge ions through the ion exit.

(22) The voltages applied to the electrodes of the ion guide may be configured such that ions are caused to (freely) migrate to (are transported to) the one or more ion exits 4, 5 under the influence of the radial force (e.g. the static electric field and/or the time varying electric field). To achieve this no trapping potential may be provided in the second (r) radial direction. It will be appreciated that in various embodiments, the radial force (e.g. the static electric field and/or the time varying electric field) will act to urge ions to the ion exit without separating them (e.g. in a non-mass selective manner), and the force urging ions through the one or more ion exits 4, 5 will act to urge ions through the one or more ion exits 4, 5 without separating them (e.g. in a non-mass selective manner), e.g. such that ions within the ion guide are caused to exit the ion guide via the one or more exits 4, 5 without being separated (e.g. in a non-mass selective manner).

(23) The overall effect of various embodiments is to guide ions from a region between the first and second plurality of electrodes to a region outside the first and second plurality of electrodes via the one or more ion exits 4, 5. Ions that arrive or that are present at any point (e.g. any angular (θ) displacement and/or any radial (r) displacement) within the first and second plurality of electrodes, and having any value of or a wide range of mass to charge ratios, will be guided through the one or more ion exits 4, 5, and will be effectively concentrated into a relatively narrow ion beam.

(24) It will therefore be appreciated that various embodiments can effectively capture, transport, confine, focus, concentrate and/or collimate annularly distributed ions, e.g. into one or more beams of ions exiting the one or more ion exits 4, 5. Ions from various distributed sources may be focused, concentrated and/or collimated into a relatively narrow diameter beam, e.g. for passage through subsequent differential apertures or ion optics.

(25) Furthermore, the design of various embodiments is relatively compact, e.g. because it does not rely on slowly urging ions to a more focused beam as the ions transit axially along a device. Thus, the ion guide advantageously has a relatively small footprint. In addition, the design of various embodiments means that the temporal fidelity of the ions arriving at the ion guide is advantageously maintained, irrespective of their entry point to the ion guide.

(26) The ion guide can be used to transport ions from an annularly distributed source, such as a cylindrical ion guide or an annular trap, etc., to the first 4 and/or second 5 ion exit. Ions appearing at any point on the circumference of the ion guide at a given time will be transported and focused to the first 4 and/or second 5 ion exit together, maintaining the temporal fidelity of the original ions.

(27) FIGS. 2 and 3 show further embodiments. The ion guides shown in FIGS. 2 and 3 are substantially similar to the ion guide of FIG. 1, and corresponding features are labelled with the same reference numerals. It will be appreciated that these embodiments may comprise any or all of the optional features described herein, as appropriate.

(28) The ion guides of FIGS. 2 and 3 are substantially similar to the ion guide of FIG. 1, except that the first 1 and second 2 arrays of electrodes are not arranged in a plane. Instead, the first 1 and second 2 arrays of electrodes are arranged in dome-shaped or cone-shaped configurations. Each electrode (or group of electrodes) of the array of electrodes may be arranged at a different displacement in the first (z) direction (i.e. in the direction of the axis around which the electrodes are concentric). The displacement in the first (z) direction of each electrode (or group of electrodes) may increase or decrease from the innermost electrode to the outermost electrode.

(29) The first 1 and second 2 arrays of electrodes may be arranged such the separation in the first (z) direction between electrodes in the first 1 and second 2 arrays of electrodes is minimum for the innermost electrodes of the arrays of electrodes, and may be maximum for the outermost electrodes of the arrays of electrodes.

(30) FIG. 2(b) illustrates a potential within the ion guide in accordance with an embodiment in which a travelling potential is used to cause ions to migrate to the ion exit(s) 4, 5, which corresponds to the potential illustrated in FIG. 1(c). FIG. 3(b) illustrates a potential within the ion guide in accordance with an embodiment in which a static DC potential is used to cause ions to migrate to the ion exit(s) 4, 5, which corresponds to the potential illustrated in FIG. 1(d).

(31) Other non-planar arrangements for the arrays of electrodes 1, 2 are possible. For example, one of the arrays of electrodes (i.e. the first 1 or second 2 array of electrodes) may be arranged in a plane, while the other array may not be arranged in a plane, e.g. may be arranged in a cone-shaped configuration.

(32) Advantageously, in these embodiments, the ion entrance region can effectively be wider (in the first (z) direction) than in the embodiment of FIG. 1. The AC or RF voltage (which acts to confine ions within the ion guide in the first (z) direction) can be used to focus ions in the first (z) direction as they migrate from the outer region of the ion guide to the ion exit(s) 4, 5. Thus, it will be appreciated that these embodiments can be used to transport ions from a more distributed source.

(33) In another embodiment, the ion guide may be operated as an Ion Mobility Separator or Spectrometer (IMS). In this embodiment, the buffer gas may be provided within the ion guide at an appropriate pressure, e.g., around 1 mbar. The buffer gas may be arranged to flow in a direction opposite to the direction in which the ions travel. As ions are urged towards the ion exit 4, 5 against the buffer gas, they may be caused to separate according to their ion mobility. Thus, the ion guide can provide a high capacity annular IMS that may be used to guide ions towards the one or more ion exits 4, 5 as ions are separated according to their ion mobility.

(34) In various embodiments, alternative shapes of the ion guide can be provided and used, e.g. square, rectangular, etc.

(35) In various embodiments, the one or more ion exits 4, 5 are not arranged at the centre of the ion guide, but in other positions within the first and/or second array. A plurality of ions exits may be provided and used, e.g. a plurality of ions exits within the first 1 and/or second 2 planar array of electrodes. Each ion exit may have a concentric arrangement of electrodes surrounding it, so that ions may be urged to the ion exit in the manner discussed above.

(36) A further embodiment is illustrated in FIG. 4. Features of the ion guide shown in FIG. 4 that correspond to features of the earlier embodiments are labelled with the same reference numerals. It will be appreciated that this embodiment may comprise any or all of the optional features described herein, as appropriate.

(37) The ion guide of FIG. 4 is effectively a portion or a sector of the ion guide of FIG. 1. The ion guide of FIG. 4 may be provided as a standalone device, i.e. as illustrated in FIG. 4(a). In this embodiment, the ion guide comprises a first array of electrodes 1 comprising a first plurality of arcuate or curved electrodes and a second array of electrodes 2 comprising a second plurality of arcuate or curved electrodes.

(38) The first and/or second plurality of arcuate or curved electrodes may comprise a plurality of circular arc-shaped electrodes. The first plurality of arcuate or curved electrodes may be arranged to be parallel to one another, e.g. in a plane, e.g. in an approximate sector or circular sector configuration. The second plurality of arcuate or curved electrodes may be arranged to be parallel to one another, e.g. in a plane, e.g. in an approximate sector or circular sector configuration.

(39) The plane in which the first plurality of electrodes are arranged and the plane in which the second plurality of electrodes are arranged may be parallel to one another (as shown in FIG. 4(a)), but this is not essential. The electrodes may be arranged such that the separation in the first (z) direction between electrodes in the first 1 and second 2 arrays of electrodes is minimum for the smallest electrodes of the arrays of electrodes (i.e. the electrodes closest to the ion exit 4), and may be maximum for the largest electrodes of the arrays of electrodes (i.e. the electrodes closest to the ion entrance 6). In other words, the arrays get closer together towards the ion exit 4.

(40) The first plurality of arcuate or curved electrodes and the second plurality of arcuate or curved electrodes may be arranged so that each of the electrodes at least partially surrounds an ion exit 4. The ion exit 4 may be located adjacent to or between the smallest electrodes in the first 1 and second 2 array of electrodes, i.e. at the geometric origin of the circular sector. An ion entrance region 6 may be located adjacent to or between the largest electrodes in the first 1 and second 2 array of electrodes, i.e. at the circumference of the circular sector.

(41) Ions may be caused to enter the ion guide via the ion entrance region 6. An AC or RF voltage is applied to the first array of electrodes 1 and to the second array of electrodes 2 so as to confine ions within the ion guide in the first (z) direction, and one or more DC voltages is applied to the first array of electrodes 1 and/or to the second array of electrodes 2 so as to urge ions within the ion guide in the second (r) direction towards the ion exit region 4, such that ions within the ion guide are caused to migrate to the ion exit region 4, i.e. in a corresponding manner as discussed above with reference to FIGS. 1-3. FIG. 4(b) shows one embodiment, where the one or more DC voltages comprises a travelling potential.

(42) In addition to this, one or more (e.g. at least two) potential barriers may be provided so as to confine ions within the ion guide in a third direction perpendicular to the first (z) direction and to the second (r) direction (e.g. the angular (θ) direction). The one or more potential barriers may be provided on either side of the ion guide so as to prevent ions leaving the ion guide in the third direction. The one or more potential barriers may be generated by applying one or more AC or RF voltages or one or more DC voltages to one or more electrodes arranged along the outer edges of the ion guide (not shown in FIG. 4(a)).

(43) The ion guide of this embodiment may advantageously be used to focus ions from a relatively diffuse source to a point or a narrow beam (in a corresponding manner as discussed above) as they migrate or are transported (and optionally as they are separated according to their ion mobility) from the ion entrance 6 to the ion exit 4. Advantageously, the curvature of the ion guide may be matched to the curvature of an incoming ion cloud such the ions are automatically brought to a focus as they migrate to the ion exit 4.

(44) In alternative embodiments, any of the ion guides of FIGS. 1-3 may be operated in a mode of operation that effectively simulates the ion guide of FIG. 4. In these embodiments, one or more (e.g. at least two) potential barriers are provided so as to confine ions within the ion guide in a third direction perpendicular to the first (z) direction and to the second (r) direction (e.g. the angular (θ) direction). The one or more potential barriers may be provided on either side of an ion guiding region so as to prevent ions leaving the ion guiding region in the third direction. The one or more potential barriers may be generated by applying one or more AC or RF voltages or one or more DC voltages to one or more electrodes arranged along either side of the ion guiding region.

(45) In an alternative embodiment, the ion guide may be used in reverse. It will be appreciated that in this embodiment, relatively concentrated ions, or ions from a point source may be distributed to form a relatively distributed or diffuse annular cloud of ions. For example, a concentrated ion beam may be distributed over a uniform annular volume.

(46) According to this embodiment, the ion guide may have the same structure as described above, although the one or more ion exit regions 4, 5 will effectively act as one or more ion entrance regions, and the one or more ion entrance regions 6, 7 will effectively acts as one or more ion exit regions. Ions within the ion guide may be urged in the second (r) (radial) direction away from the one or more apertures or ion entrance regions 4, 5, such that ions at some, most or all angular (θ) displacements within the ion guide are caused to migrate away from the one or more apertures or ion entrance regions 4, 5, and may be caused to exit the ion guide via the one or more ion exit regions 6, 7.

(47) The ion guide may be used in conjunction with an analytical ion trap that has a curved or annular trapping region to deliver ions from a point source to the curved or annular trapping region and/or for capturing and compressing annularly ejected ions from the curved or annular trapping region to the exit region of the ion guide.

(48) It will be appreciated from the above that various embodiments can advantageously provide a relatively compact device that acts to capture, transport and concentrate an extended cloud of ions to a point, e.g. for subsequent transmission/analysis.

(49) 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.