RF ion guide with axial fields

Patent metadata

Field	Value
Publication number	US-9613788-B2
Application number	US-201514734916-A
Country	US
Kind code	B2
Filing date	Jun 9, 2015
Priority date	Jun 13, 2014
Publication date	Apr 4, 2017
Grant date	Apr 4, 2017

Abstract

RF ion guides are configured as an array of elongate electrodes arranged symmetrically about a central axis, to which RF voltages are applied. The RF electrodes include at least a portion of their length that is semi-transparent to electric fields. Auxiliary electrodes are then provided proximal to the RF electrodes distal to the ion guide axis, such that application of DC voltages to the auxiliary electrodes causes an auxiliary electric field to form between the auxiliary electrodes and the ion guide RF electrodes. A portion of this auxiliary electric field penetrates through the semi-transparent portions of the RF electrodes, such that the potentials within the ion guide are modified. The auxiliary electrode structures and voltages can be configured so that a potential gradient develops along the ion guide axis due to this field penetration, which provides an axial motive force for collision damped ions.

First claim

The invention claimed is:

1. An apparatus, comprising:
an ion source;
a mass analyzer; and
an RF ion guide positioned in an ion path between the ion source and the mass analyzer, the RF ion guide having an ion guide axis extending between an input end of the RF ion guide and an exit end of the RF ion guide, the RF ion guide comprising:
a first electrode extending along the ion guide axis, the first electrode configured to be connected to a voltage source; and
a second electrode extending along the ion guide axis, the second electrode configured to be connected to a RF source, a portion of the second electrode being positioned between the first electrode and the ion guide axis, the second electrode comprising a plurality of openings, wherein during use of the apparatus, the second electrode produces RF electric fields within a central portion of the RF ion guide throughout a region between the second electrode and the ion guide axis to radially confine ions,
wherein the first and second electrodes are configured so that during operation of the RF ion guide, a DC electric field is generated between the first and second electrodes, resulting in a DC electric field at the ion guide axis that has a non-zero axial component.

2. The apparatus of claim 1 , wherein the first electrode is configured to generate an electric field that impinges on the ion guide axis, the electric field configured to pass through one or more openings of the second electrode in a direction approximately perpendicular to the ion guide axis.

3. The apparatus of claim 1 , wherein the first electrode is configured to produce a first electric potential at the input end of the ion guide axis and a second electric potential at the exit end of the ion guide axis, the first electric potential being different from the second electric potential.

4. The apparatus of claim 1 , wherein the second electrode comprises a planar conductor, and the plurality of openings comprises a grid.

5. The apparatus of claim 4 , wherein the grid has a grid density that varies along a direction of the ion guide axis.

6. The apparatus of claim 4 , wherein the RF ion guide comprises three additional electrodes extending along the ion guide axis, each of the additional electrode comprising a planar conductor, where each planar conductor is located on the opposite side of the ion guide axis from and parallel to the planar conductor of another of the additional electrodes.

7. The apparatus of claim 6 , wherein the RF ion guide comprises further electrodes including the first electrode, each of the further electrodes extending along the ion guide axis, each of the planar conductors being positioned between the ion guide axis and a corresponding one of the further electrodes.

8. The apparatus of claim 4 , wherein the first electrode extends along the ion guide axis and is non-parallel to the ion guide axis.

9. The apparatus of claim 8 , wherein the second electrode is tilted with respect to the ion guide axis, and the first electrode is titled at a different angle from the second electrode such that an axial field gradient is independent of a tilt angle of the second electrode.

10. The apparatus of claim 5 , wherein the first electrode extends parallel to the planar conductor of the second electrode.

11. The apparatus of claim 5 , wherein the RF ion guide comprises three additional electrodes extending along the ion guide axis, each of the additional electrode comprising a planar conductor, where each planar conductor is located on an opposite side of the ion guide axis from and parallel to the planar conductor of another of the additional electrodes, and the first electrode comprises a cylindrical conductor symmetrically enclosing the planar conductors.

12. The apparatus of claim 1 , wherein the second electrode comprises a hollow cylindrical conductor extending along the ion guide axis, the second electrode having a plurality of slots having different slot width, and the first electrode comprises a rod positioned inside the hollow cylindrical conductor.

13. The apparatus of claim 1 , wherein the second electrode has a first cross-sectional area at the input end that is different from a second cross-sectional area at the exit end.

14. The apparatus of claim 1 , wherein the second electrode is configured to provide collision cooling to ions entering through the input end of the RF ion guide.

15. The apparatus of claim 1 , wherein the first electrode comprises a plurality of conductors, each conductor being connected to a different voltage source to provide an electric field profile along the ion guide axis.

16. The apparatus of claim 1 , wherein the RF ion guide is configured to cause collision induced dissociation of ions entering through the input end of the RF ion guide.

17. A method, comprising:
ionizing a sample to generate ions;
introducing the ions through an input end of a RF ion guide to collide with background gas in the RF ion guide;
providing a DC electric field along an ion guide axis of the RF ion guide that has a non-zero axial component to cause ions that have undergone collisions to exit the RF ion guide; and
mass analyzing the ions that have undergone collisions and exited the RF ion guide,
wherein providing the axial electric field comprises applying a DC voltage to a first electrode of the RF ion guide that surrounds a second electrode of the RF ion guide such that an electric field produced by the first electrode penetrates a central portion of the second electrode before impinging on the ion guide axis to generate a DC electric field between the first and second electrodes, the central portion of the second electrode comprises a plurality of openings, and wherein the second electrode produces RF electric fields within a central portion of the RF ion guide throughout a region between the second electrode and the ion guide axis to radially confine ions.

18. The method of claim 17 , further comprising varying the DC voltage applied to the first electrode to provide a time-dependent moving local potential well within the RF ion guide to control motions of ions along the ion guide axis.

19. The method of claim 17 , further comprising varying the DC voltage applied to the first electrode to locally trap positive and negative ions in separate potential wells and merging the positive and negative ions to effect ion-ion reaction.

20. The method of claim 17 , wherein the ions that have undergone collisions has a reduced radial distribution compared to ions that have not undergone collisions.

21. The method of claim 17 , further comprising fragmenting the ions introduced through the input end by collision induced dissociation.

22. An RF ion guide, the RF ion guide having an ion guide axis extending between an input end of the RF ion guide and an exit end of the RF ion guide, the RF ion guide comprising:
a voltage source;
a RF source;
a first electrode extending along the ion guide axis, the first electrode configured to be connected to the voltage source; and
a second electrode extending along the ion guide axis, the second electrode configured to be connected to the RF source, the second electrode being positioned between the first electrode and the ion guide axis, the second electrode comprising a plurality of openings, wherein during use of the apparatus, the second electrode produces RF electric fields within a central portion of the RF ion guide throughout a region between the second electrode and the ion guide axis to radiall

Assignees

• Perkinelmer Health Sci Inc

Inventors

• Welkie David G

Classifications

• H01J49/0045

  characterised by the fragmentation or other specific reaction · CPC title

• H01J49/063 Primary

  Multipole ion guides, e.g. quadrupoles, hexapoles · CPC title

• H01J49/0031

  Step by step routines describing the use of the apparatus (H01J49/0081 takes precedence) · CPC title

• H01J49/062 Primary

  Ion guides (linear ion traps performing mass selection H01J49/4225, mass filters H01J49/421) · CPC title

• H01J49/005

  by collision with gas, e.g. by introducing gas or by accelerating ions with an electric field · CPC title