Trapped ion mobility spectrometer with high ion storage capacity

Patent metadata

Field	Value
Publication number	US-10458944-B2
Application number	US-201615172237-A
Country	US
Kind code	B2
Filing date	Jun 3, 2016
Priority date	Jun 3, 2016
Publication date	Oct 29, 2019
Grant date	Oct 29, 2019

Abstract

The invention is related to a trapped ion mobility spectrometer (TIMS device) and proposes to use higher order (order N>2) linear multipole RF systems to accumulate and analyze ions at an electric DC field barrier, either pure higher order RF multipole systems or multipole RF systems with transitions from higher order towards lower order, e.g. from a linear octopolar RF system (N=4) to a linear quadrupole RF system (N=2) in front of the apex of the electric DC field barrier.

First claim

The invention claimed is:

1. A trapped ion mobility analyzer comprising an electric DC field barrier in the form of a ramp, a counteracting gas flow that drives ions against the electric DC field barrier, such that ions are trapped and separated along the ramp according to their mobilities, and an RF ion guide that generates an RF multipole field with an order higher than an RF quadrupolar field (N=2), such that ion density in the multipole field is highest away from an axis of the ion guide, allowing for accumulation of a relatively high number of ions without losses due to space charge effects.

2. The trapped mobility analyzer according to claim 1 , wherein the RF multipole field with order N>2 extends along the electric DC field barrier.

3. The trapped ion mobility analyzer according to claim 2 , wherein the RF ion guide additionally generates an RF quadrupolar field (N=2) which is substantially weaker than the RF multipole field with order N>2.

4. The trapped ion mobility analyzer according to claim 1 , wherein the RF ion guide additionally generates an RF quadrupolar field (N=2) which is substantially weaker than the RF multipole field with order N>2 along a first portion of the ion guide and is substantially stronger than the RF multipole field with order N>2 along a second portion of the ion guide.

5. The trapped mobility analyzer according to claim 4 , wherein the RF quadrupolar field is stronger than the RF multipole field with order N>2 adjacent to and/or on the apex of the electric DC field barrier.

6. The trapped mobility analyzer according to claim 5 , wherein the RF quadrupolar field is stronger than the RF multipole field with order N>2 adjacent to the beginning and along at least a part of the a plateau of the electric DC field barrier.

7. The trapped mobility analyzer according to claim 1 , wherein the RF multipole field with order N>2 transitions into an RF multipole field of lower order along the RF ion guide.

8. The trapped mobility analyzer according to claim 7 , wherein the ion guide comprises a system of 16 rows of inner electrodes which are supplied with electric RF potentials and generates a transition from an octopolar RF multipole field into a quadrupolar RF field.

9. The trapped mobility analyzer according to claim 7 , wherein the ion guide comprises a system of 24 rows of inner electrodes which are supplied with electric RF potentials and generates a transition from a dodecapolar RF field, optionally via a hexapolar RF field, into a quadrupolar RF field.

10. The trapped ion mobility analyzer according to claim 1 , wherein the RF multipole field with order N>2 is one of a hexapolar (N=3), octopolar (N=4) and dodecapolar (N=6) RF field or an RF field of an ion guide with stacked apertured electrodes.

11. The trapped ion mobility spectrometer according to claim 1 , wherein a flexible PCB board is rolled or folded to form the RF ion guide comprising the inner electrodes on one side and electric connections and components on the other side.

12. The trapped ion mobility analyzer according to claim 1 , wherein a laminar gas flow is formed by a gas-tight tube which has a greater inner diameter at the entrance and a smaller inner diameter at the exit.

13. The trapped ion mobility spectrometer according to claim 12 , wherein an RF multipole field of at least third order is generated in a segment of the tube with greater diameter, whereas a quadrupole RF field is prevailing in a segment with smaller diameter at the exit.

14. A mass spectrometric system comprising a trapped ion mobility analyzer comprising an electric DC field barrier in the form of a ramp, a counteracting gas flow that drives ions against the electric DC field barrier such that ions are trapped and separated along the ramp according to their mobilities, and an RF ion guide, the ion guide generating an RF multipole field with an order higher than a quadrupolar RF field (N=2), such that ion density in the multipole field is highest away from an axis of the ion guide, allowing for accumulation of a relatively high number of ions without losses due to space charge effects, and a downstream mass analyzer.

15. The mass spectrometric system according to claim 14 , wherein the mass analyzer is one of a time-of-flight mass analyzer with orthogonal ion injection, an electrostatic ion trap, an RF ion trap, a quadrupole mass filter, and an ion cyclotron frequency mass analyzer.

16. The mass spectrometric system according to claim 14 , wherein a quadrupole mass filter and a downstream fragmentation cell are positioned between the ion mobility analyzer and the mass analyzer.

17. A method for operating a trapped ion mobility analyzer, comprising the steps of:
(a) generating ions in an ion source;
(b) transferring the ions into an ion guide;
(c) radially confining the ions in the ion guide by an RF multipole field with an order higher than an RF quadrupolar field (N=2), such that ion density in the multipole field is highest away from an axis of the ion guide, allowing for accumulation of a relatively high number of ions without losses due to space charge effects;
(d) axially trapping the ions in the ion guide by an electric DC field ramp and a counteracting gas flow that drives the ions against the electric DC field ramp such that the ions are separated along the ramp according to their mobilities; and
(e) releasing the trapped ions from the ion guide according to their mobility by changing the electric DC field and/or the gas flow.

18. The method according to claim 17 , wherein the amount of transferred ion species is so high that the ion density of at least one ion species is highest at an off-axis position along at least a part of the complete ion guide due to the space charge of the transferred ions.

19. The method according to claim 18 , wherein the at least one ion species is released from the ion guide on an off-axis position.

20. The method according to claim 18 , wherein the ions are radially confined by an RF multipole field with an order N>2 along an upstream part of the ion guide and by a quadrupolar RF field along a more downstream part of the ion guide, and wherein the ions are released from the ion guide on-axis at the more downstream part of the ion guide.

Assignees

• Bruker Daltonik Gmbh

Inventors

• Räther Oliver
• Betz Thomas
• Park Melvin Andrew

Classifications

• H01J49/4225

  Multipole linear ion traps, e.g. quadrupoles, hexapoles · CPC title

• H01J49/06

  Electron- or ion-optical arrangements · CPC title

• H01J49/0031

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

• H01J49/4215

  Quadrupole mass filters (H01J49/4225 takes precedence) · CPC title

• H01J49/426

  Methods for controlling ions · CPC title