ABRIDGED MULTIPOLE STRUCTURE FOR THE TRANSPORT AND SELECTION OF IONS IN A VACUUM SYSTEM

• US 20120305758A1
• Filed: 06/03/2011
• Published: 12/06/2012
• Est. Priority Date: 06/03/2011
• Status: Active Grant

• Current Assignee: Bruker Daltonics, Inc. (Bruker Corporation)
• Original Assignee: Bruker Daltonics, Inc. (Bruker Corporation)
• Inventors: PARK, Melvin Andrew
• Granted Patent: US 9,184,040 B2
• Time in Patent Office: Days
• US Class Current: 250/282
• CPC Class Codes: H01J 49/063 Multipole ion guides, e.g. quadrupoles, hexapoles
• CPC Class Codes: H01J 49/421 Mass filters, i.e. deviating unwanted ions without trapping
• CPC Class Codes: H01J 49/4235 Stacked rings or stacked plates
• CPC Class Codes: H01J 49/4255 with particular constructional features

Abstract

An abridged multipole structure for the transport and selection of ions along a central axis in a vacuum system is constructed from a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension. When a voltage is applied across the second dimension, an electrical potential is produced at the planar face whose amplitude is a linear function of position along the second dimension. Two electrode structures can be arranged parallel to each other with the first dimension extending along the central axis or more electrodes structures can be arranged to form multipole structures with various polygonal cross sections.

Claims

1. An abridged multipole structure for the transport and selection of ions along a central axis in a vacuum system, comprising:

a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension and being constructed so that a voltage applied across the second dimension produces an electrical potential at the planar face whose amplitude is a linear function of position along the second dimension; and

a mechanism that positions the plurality of rectilinear electrode structures so that, for each electrode structure, the planar face faces the central axis and the first dimension extends along the central axis.

2. The structure of claim 1 wherein each electrode structure is comprised of a plurality of elements arranged in a stack extending across the second dimension, wherein each element is a strip with a long dimension extending along the central axis.

3. The structure of claim 2 wherein each of the plurality of elements is an electrically conductive electrode.

4. The structure of claim 3 wherein the plurality of electrodes in the stack are spaced at equal intervals across the second dimension.

5. The structure of claim 2 wherein each of said elements is comprised of an electrically resistive layer and a plurality of electrically conductive layers, all of the layers being mounted on at least one insulating support.

6. The structure of claim 5 wherein the resistive layer is positioned on the planar face.

7. The structure of claim 5 wherein the electrically resistive layer and the plurality of electrically conductive layers are shaped and positioned on the support so that the electrically resistive layer and the plurality of conductive layers are capacitively coupled to the extent that an application of a voltage between the conductive layers produces a potential on the electrically resistive layer which varies substantially linearly with respect to position on the electrically resistive layer between the conductive layers.

8. The structure of claim 1 wherein the mechanism that positions the plurality of rectilinear electrode structures positions the electrode structures so that a cross section of the electrode structures perpendicular to the central axis is a polygon.

9. The structure of claim 8 wherein the polygon is a hexagon.

10. The structure of claim 8 wherein the polygon is a rectangle.

11. The structure of claim 8 wherein the polygon is a square.

12. The structure of claim 1 wherein the mechanism that positions the plurality of rectilinear electrode structures positions two electrode structures parallel to each other and on opposite sides of said central axis.

13. The structure of claim 1 wherein the vacuum system includes a first chamber and a second chamber and a pumping restriction between the first and second chambers and wherein the mechanism that positions the plurality of rectilinear electrode structures positions the electrode structures to form a closed tubular structure having a first end positioned in the first chamber and a second end positioned in the second chamber and extending through the pumping restriction so that ions may be transported from the first chamber to the second chamber via the closed tubular structure, but flow of gas between the first and second chambers is restricted.

14. The structure of claim 13 wherein the inscribed diameter of the tubular structure is larger at the first end than the inscribed diameter at the second end.

15. An abridged multipole structure for the transport and selection of ions along a plurality of axes in a vacuum system, comprising:

a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension and being constructed so that a voltage applied across the second dimension produces an electrical potential at the planar face whose amplitude is a linear function of position along the second dimension; and

a mechanism that positions the plurality of rectilinear electrode structures so that, for each electrode structure, the planar face faces one of the plurality of axes and the first dimension extends along that one axis.

16. A mass spectrometer comprising:

an ion source;

a vacuum system having a central axis;

an ion detector; and

an abridged multipole structure for the transport and selection of ions along the central axis including a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension and being constructed so that a voltage applied across the second dimension produces an electrical potential at the planar face whose amplitude is a linear function of position along the second dimension; and

a mechanism that positions the plurality of rectilinear electrode structures so that, for each electrode structure, the planar face faces the central axis and the first dimension extends along the central axis.

17. A method for transporting and selecting ions along a central axis in a vacuum system, comprising:

(a) providing a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension and being constructed so that a voltage applied across the second dimension produces an electrical potential at the planar face whose amplitude is a linear function of position along the second dimension;

(b) positioning the plurality of rectilinear electrode structures so that, for each electrode structure, the planar face faces the central axis and the first dimension extends along the central axis; and

(c) applying a voltage across each electrode structure second dimension.

18. The method of claim 17 wherein step (c) comprises applying a voltage including an RF component across each electrode structure second dimension.

19. The method of claim 18 wherein the RF component that is applied across each electrode structure second dimension produces a multipole field in the vicinity of the rectilinear electrode structures.

20. The method according to claim 19 further comprising:

(d) providing a source of analyte ions; and

(e) injecting the analyte ions into the vacuum system along the central axis between the plurality of rectilinear electrode structures so that the RF multipole field produced by the plurality of rectilinear electrode structures confines ions radially about the central axis.

21. The method of 18 wherein step (b) comprises positioning four electrode structures to form a multipole structure having a square cross section and step (c) comprises applying voltages to the four electrode structures to produce an electrical potential within the multipole structure that has an amplitude Φ

(t) according to the equation

22. The method of claim 21 wherein the waveform Φ

_o(t) includes an RF and a DC component.

23. The method of claim 22 wherein the waveform Φ

_o(t) includes additional terms generates potentials which are linear functions of position along the second dimensions of each electrode structure resulting in the formation simultaneously with the multipole field, a substantially homogeneous dipole field having field lines orthogonal to said central axis.

24. The method of claim 22 further comprising:

(d) providing a source of analyte ions;

(e) injecting the analyte ions along the central axis into the multipole structure; and

(f) selecting the amplitude and frequency of the RF component and the magnitude of the DC component such that ions of a predetermined mass or mass range follow stable trajectories through the multipole structure whereas ions outside said mass range follow unstable trajectories and are not transmitted through the multipole structure.

25. The method of claim 24 further comprising:

(g) arranging the four electrode structures such that gaps exist between the electrode structures;

(h) providing ion detectors positioned adjacent to said gaps; and

(i) detecting ions which follow unstable trajectories and pass out of the multipole structure through said gaps.

26. A method for the transport and selection of ions along a central axis, comprising:

(a) providing a plurality of rectilinear electrode structures, each having a substantially planar face with a first dimension and a second dimension perpendicular to the first dimension and being constructed so that a voltage applied across the second dimension produces an electrical potential at the planar face whose amplitude is a linear function of position along the second dimension;

(b) positioning the plurality of rectilinear electrode structures so that, for each electrode structure, the planar face faces the central axis and the first dimension extends along the central axis to form a multipole structure; and

(c) applying potentials to the electrode structures such that the electrode structures generate potentials which are linear functions of position along the second dimensions of each electrode structure in order to form a substantially homogeneous dipole field having field lines orthogonal to said central axis.

27. The method of claim 26 wherein said homogeneous dipole field is a periodic function of time.

28. The method of claim 27 wherein said homogeneous dipole field has a fixed amplitude and rotates about the central axis.

29. The method of claim 26 wherein step (c) comprises applying potentials including an RF component to the electrode structures in order to produce a multipole field simultaneously with the dipole field.

30. The method according to claim 26 wherein step (c) comprises applying potentials including an RF component to the electrode structures and the method further comprises:

(d) providing a source of analyte ions;

(e) injecting the analyte ions along the central axis into the multipole structure; and

(f) selecting an amplitude and frequency of the RF component and an amplitude and frequency of oscillation of the homogeneous dipole field to excite motion of ions having masses within a predetermined mass range.

31. A method according to claim 30 wherein step (f) comprises selecting an amplitude and frequency of the RF component and an amplitude and frequency of oscillation of the homogeneous dipole field to excite ions having masses within a predetermined mass range to a range of motion sufficient to remove the ions from the multipole structure by causing the ions to impinge onto the electrode structures or to be ejected from the multipole structure.