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

• US 20120305759A1
• Filed: 07/07/2011
• 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 8,927,940 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 49/424 Three-dimensional ion traps, i.e. comprising end-cap and ring electrodes

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. Additional embodiments can act as linear ion traps or Paul ion traps.

Claims

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

a first plurality of rectilinear electrode structures, each structure 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;

a mechanism that positions the first plurality of rectilinear electrode structures so that, for each electrode structure, the first dimension extends along the central axis and the planar faces of the electrode structures are positioned symmetrically about the central axis; and

a pair of trapping electrodes extending perpendicularly to the central axis and positioned before and after the first plurality of electrode structures along the central axis.

2. The structure of claim 1 wherein each trapping electrode is planar.

3. The structure of claim 1 wherein each trapping electrode has an aperture therein positioned on the central axis.

4. The structure of claim 1 further comprising a prefilter structure formed from a second plurality of rectilinear electrode structures, each structure 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, the second plurality of rectilinear electrode structures being positioned with the first dimension extending along the central axis and the planar faces of the electrode structures parallel to the first plurality of electrode structures and being positioned symmetrically about the central axis, the prefilter structure being located between one of the trapping electrodes and the first plurality of electrode structures.

5. The structure of claim 4 further comprising a postfilter structure formed from a third plurality of rectilinear electrode structures, each structure 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, the third plurality of rectilinear electrode structures being positioned with the first dimension extending along the central axis and the planar faces of the electrode structures parallel to the first plurality of electrode structures and being positioned symmetrically about the central axis, the postfilter structure being located between one of the trapping electrodes and the first plurality of electrode structures.

6. The structure of claim 5 wherein the first plurality of rectilinear electrode structures comprises a first pair of electrode structures, the second plurality of rectilinear electrode structures comprises a second pair of electrode structures and the third plurality of rectilinear electrode structures comprises a third pair of electrode structures and wherein the first, second and third pairs of electrode structures are positioned with the planar faces of each pair of electrode structures parallel to each other and on opposing sides of the central axis and the planar faces of the first, second and third pairs of electrode structures are parallel to each other.

7. The structure of claim 1 wherein the first plurality of rectilinear electrode structures comprises a first pair of electrode structures and the mechanism positions the first pair of rectilinear electrode structures so that the planar faces of the electrode structures are positioned parallel to each other and on opposing sides of the central axis.

8. A mass spectrometer comprising:

an ion source;

a vacuum system having a central axis;

an ion detector; and

an abridged multipole structure having three pluralities of rectilinear electrode structures positioned sequentially along the central axis, each electrode structure 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, a mechanism that positions each plurality of rectilinear electrode structures so that, for each electrode structure, the first dimension extends along the central axis and the planar faces of the plurality of electrode structures are positioned symmetrically about the central axis; and

a pair of trapping electrodes extending perpendicularly to the central axis and positioned before and after the three pluralities of electrode structures along the central axis.

9. The mass spectrometer of claim 8 further comprising an RF voltage source for applying RF voltages to the three pluralities of rectilinear electrode structures in order to confine ions produced by the ion source along the central axis.

10. The mass spectrometer of claim 9 further comprising a DC voltage source for applying DC voltages to the three pluralities of rectilinear electrode structures in order to trap ions produced by the ion source in a center plurality of rectilinear electrode structures located between two other pluralities of rectilinear electrode structures.

11. The mass spectrometer of claim 10 further comprising an AC voltage source for applying an AC dipole voltage to the center plurality of rectilinear electrode structures.

12. The mass spectrometer of claim 11 wherein the ion detector is located adjacent the center plurality of rectilinear electrode structures and positioned parallel to the central axis.

13. The mass spectrometer of claim 8 wherein the three pluralities of rectilinear electrode structures comprises a first pair of electrode structures, a second pair of electrode structures and a third pair of electrode structures and wherein the first, second and third pairs of electrode structures are positioned with the planar faces of each pair of electrode structures parallel to each other and on opposing sides of the central axis and the planar faces of the first, second and third pairs of electrode structures are parallel to each other.

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

a plurality of planar electrodes positioned perpendicularly to the central axis at equal intervals along the central axis, each electrode having a circular central aperture centered on the central axis, the plurality of electrodes arranged so that the radii of the central apertures increases linearly from a minimum radius to a maximum radius with respect to increasing position along the central axis and then decreases linearly from the maximum radius to the minimum radius with respect to increasing position along the central axis; and

a source that applies voltages to each electrode, the voltage applied to each electrode increasing linearly from a minimum value to a maximum value with respect to increasing position of that electrode along the central axis and then decreases linearly from the maximum value to the minimum value with respect to increasing position of that electrode the central axis.

15. The structure of claim 14 wherein the plurality of electrodes are separated from each other by a plurality of insulating spacers located therebetween.

16. The structure of claim 15 wherein each spacer comprises a wafer of insulating material having a central aperture, the central apertures of the spacers being sized such that the surfaces of the spacer central apertures are recessed from the surfaces of the electrode central apertures.

17. The structure of claim 15 wherein the plurality of electrodes and spacers are sandwiched between two baseplates and the source applies a voltage across the baseplates.

18. The structure of claim 17 wherein a capacitive divider evenly divides the voltage across the baseplates and applies voltages to each electrode.

19. The structure of claim 18 wherein each electrode has a face with an area and the areas of the plurality of electrodes are the same.

20. The structure of claim 18 wherein a resistive divider evenly divides the voltage across the baseplates and applies voltages to each electrode.

21. The structure of claim 17 wherein a resistive divider evenly divides the voltage across the baseplates and applies voltages to each electrode.

22. The structure of claim 14 further comprising a second voltage source that applies a voltage to the plurality of electrodes that is a dipole potential.

23. The structure of claim 22 wherein an amplitude of the dipole potential varies linearly with position along the central axis.

24. The structure of claim 22 wherein an amplitude of the dipole potential varies with time.

25. An array of abridged multipole structures for the transport, selection and trapping of ions along a plurality of parallel axes in a vacuum system, comprising:

a plurality of planar electrodes positioned perpendicularly to the axes at equal intervals along the central axis, each electrode having a circular central aperture centered on each of the plurality of axes, the plurality of electrodes arranged so that the radii of the central apertures along an axis increases linearly from a minimum radius to a maximum radius with respect to increasing position along that axis and then decreases linearly from the maximum radius to the minimum radius with respect to increasing position along that axis; and

a source that applies voltages to each electrode, the voltage applied to each electrode increasing linearly from a minimum value to a maximum value with respect to increasing position of that electrode along the axes and then decreases linearly from the maximum value to the minimum value with respect to increasing position of that electrode the axes.

26. The structure of claim 25 wherein the plurality of electrodes are separated from each other by a plurality of insulating spacers located therebetween.

27. The structure of claim 26 wherein the plurality of electrodes and spacers are sandwiched between two baseplates and the source applies a voltage across the baseplates.

28. The structure of claim 27 wherein a capacitive divider evenly divides the voltage across the baseplates and applies voltages to each electrode.

29. The structure of claim 28 wherein a resistive divider evenly divides the voltage across the baseplates and applies voltages to each electrode.

30. A method for the transport, selection and trapping of ions along a central axis in a vacuum system, comprising:

(a) providing a first 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 first plurality of rectilinear electrode structures so that, for each electrode structure, the first dimension extends along the central axis and the planar faces of the electrode structures are positioned symmetrically about the central axis;

(c) positioning a pair of trapping electrodes extending perpendicularly to the central axis and located before and after the first plurality of electrode structures along the central axis;

(d) introducing ions into the first plurality of electrode structures; and

(e) applying RF voltages to the first plurality of rectilinear electrode structures in order to confine the ions along the central axis.

31. The method of claim 30 further comprising applying DC voltages to the pair of trapping electrodes in order to trap the ions in the plurality of electrode structures.

32. The method of claim 30 further comprising providing a prefilter structure formed from a second 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 positioning the prefilter structure with the first dimension extending along the central axis, the planar faces of the electrode structures being parallel to the first plurality of electrode structures and symmetrically located about the central axis and locating the prefilter structure between one of the trapping electrodes and the first plurality of electrode structures.

33. The method of claim 32 further comprising providing a postfilter structure formed from a third 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 positioning the postfilter structure with the first dimension extending along the central axis, the planar faces of the electrode structures being parallel to the first plurality of electrode structures and positioned symmetrically about the central axis and locating the postfilter structure between one of the trapping electrodes and the first plurality of electrode structures.

34. The method of claim 33 further comprising applying RF voltages to the three pluralities of rectilinear electrode structures in order to confine the ions along the central axis.

35. The method of claim 34 further comprising applying DC voltages to the three pluralities of rectilinear electrode structures in order to trap the ions in a center plurality of rectilinear electrode structures located between two other pluralities of rectilinear electrode structures.

36. The method of claim 35 further comprising applying an AC dipole voltage to the center plurality of rectilinear electrode structures.

37. The method of claim 36 wherein the three pluralities of rectilinear electrode structures comprises a first pair of electrode structures, a second pair of electrode structures and a third pair of electrode structures and wherein the first, second and third pairs of electrode structures are positioned with the planar faces of each pair of electrode structures parallel to each other and on opposing sides of the central axis and the planar faces of the first, second and third pairs of electrode structures are parallel to each other.