Method and apparatus for trapping ions by increasing trapping voltage during ion introduction

• US 5,399,857 A
• Filed: 05/28/1993
• Issued: 03/21/1995
• Est. Priority Date: 05/28/1993
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Doroshenko, Vladimir M., Cotter, Robert J.
• Primary Examiner(s): Berman, Jack I.
• Assistant Examiner(s): Beyer, James
• Application Number:
  US08/068,697
• Time in Patent Office: 662 Days
• Field of Search: 250/282, 250/291, 250/292, 250/283, 250/290, 250/286, 250/288 R
• US Class Current: 250/292
• CPC Class Codes: H01J 49/164 Laser desorption/ionisation, e.g. matrix-assisted laser desorption/ionisation [MALDI] sample holders H01J49/0418
• CPC Class Codes: H01J 49/424 Three-dimensional ion traps, i.e. comprising end-cap and ring electrodes
• CPC Class Codes: H01J 49/4295 Storage methods

Abstract

A method and apparatus for trapping ions in an ion trap having a ring electrode and a plurality of end-cap electrodes. Ions are introduced into a ion trap cavity of the ion trap from an external source or by desorption of a substance in the ion trap cavity. In a first embodiment, as the ions are introduced in the ion trap cavity, the amplitude of an RF voltage being applied to the ring electrode is gradually increased to trap the ions in the ion trap cavity. In a second embodiment, as the ions are introduced in the ion trap cavity, a retarding voltage is applied to the end-caps to reduce the initial kinetic energy of the ions. In a third embodiment, as the ions are introduced in the ion trap cavity from a probe tip inserted in the cavity, a retarding voltage is applied to the probe tip.

Claims

1. A method for trapping ions in an ion trapping field of an ion trapping device having a ring electrode and at least one end cap electrode, comprising the steps of:

introducing ions into said ion trapping field, each of said ions having an initial kinetic energy; and

applying an alternating voltage, having a first amplitude, to said ring electrode and increasing, at a predetermined gradual rate, said first amplitude to a second amplitude during a period of time when said ions are being introduced into said ion trapping field to trap said ions in said ion trapping field.

2. A method as claimed in claim 1, further comprising a step of applying a voltage to said at least one end cap electrode to reduce said initial kinetic energy of said each of said ions being introduced into said ion trapping field.

3. A method as claimed in claim 1, wherein said predetermined gradual rate is substantially linear.

4. An apparatus as claimed in claim 1, wherein said introducing step comprises the steps of:

introducing a substance into an area in which said ion trapping field will exist and bounded by said ring electrode and said at least one end cap electrode; and

directing a light beam onto said substance to create said ions.

5. A method as claimed in claim 1, wherein said introducing step introduces said ions into said ion trapping field from an external source.

6. A method as claimed in claim 2, further comprising the step of removing said voltage from said at least one end cap electrode when said alternating voltage causes said ions to be trapped in said ion trapping field.

7. A method as claimed in claim 1, wherein said introducing step further comprises the steps of:

inserting a probe having a substance thereon into said ion trapping device; and

forming said ions from said substance to cause said ions to be introduced into an area in which said ion trapping field will exist and bounded by said ring electrode and said at least one end cap electrode.

8. A method as claimed in claim 7, further comprising the step of applying a first voltage to said probe to reduce said initial kinetic energy of said each of said ions being introduced into said ion trapping field.

9. A method as claimed in claim 8, further comprising a step of applying a second voltage, different from said first voltage, to said at least one end cap electrode when said first voltage is being applied to said probe.

10. A method as claimed in claim 7, wherein said predetermined gradual rate is substantially linear.

11. A method as claimed in claim 7, wherein said forming step comprises the step of directing a light beam onto said substance to create said ions.

12. A method as claimed in claim 8, further comprising the steps of:

removing said first voltage from said probe when said alternating voltage causes said ions to be trapped in said ion trapping field; and

applying a second voltage to said at least one end cap electrode after said first voltage is removed from said probe.

25. A method according to claim 1 wherein said introducing step directs ions created at a non-centered portion of said ion trapping field toward a center portion of said ion trapping field.

26. A method as claimed in claim 25, further comprising a step of applying a voltage to said at least one end cap electrode to reduce said initial kinetic energy of said each of said ions being introduced into said ion trapping field.

27. A method as claimed in claim 25, wherein said predetermined gradual rate is substantially linear.

28. A method as claimed in claim 26, wherein said predetermined gradual rate is substantially linear.

29. A method as claimed in claim 26, further comprising the step of removing said voltage from said at least one end cap electrode when said alternating voltage causes said ions to be trapped in said ion trapping field.

13. An apparatus for trapping ions, comprising:

a ring electrode;

at least one end cap electrode;

means for introducing ions into an ion trapping field, each of said ions having an initial kinetic energy; and

means for applying an alternating voltage, having a first amplitude, to said ring electrode to create said ion trapping field and increasing, at a predetermined gradual rate, said first amplitude to a second amplitude during a period of time when said ions are being introduced into said ion trapping field to trap said ions in said ion trapping field.

14. An apparatus as claimed in claim 13, further comprising means for applying a voltage to said at least one end cap electrode to reduce said initial kinetic energy of said each of said ions being introduced into said ion trapping field.

15. A method as claimed in claim 13, wherein said predetermined gradual rate is substantially linear.

16. An apparatus as claimed in claim 13, wherein said introducing means comprises:

means for introducing a substance into an area in which said ion trapping field will exist and bounded by said ring electrode and said at least one end cap electrode; and

means for directing a light beam onto said substance to create said ions.

17. An apparatus as claimed in claim 13, wherein said introducing means comprises means for introducing said ions into said ion trapping field from an external source.

18. An apparatus as claimed in claim 14, further comprising means for removing said voltage from said at least one end cap electrode when said alternating voltage causes said ions to be trapped in said ion trapping field.

19. An apparatus as claimed in claim 13, wherein said ion introducing means comprises:

substance introducing means for introducing a substance into an area in which said ion trapping field will exist and bounded by said ring electrode and said at least one end cap electrode; and

means for causing said ion introducing means to introduce said ions into said ion trapping field from said substance.

20. An apparatus as claimed in claim 19, wherein said predetermined gradual rate is linear.

21. An apparatus as claimed in claim 19, further comprising means for applying a first voltage to said substance introducing means to reduce said initial kinetic energy of said each of said ions introduced by said ion introducing means.

22. An apparatus as claimed in claim 21, further comprising means for applying a second voltage, different from said first voltage, to said at least one end cap electrode when said first voltage applying means applies said first voltage to said substance introducing means.

23. An apparatus as claimed in claim 19, wherein said ion introducing means comprises means for directing a light beam onto said substance to create said ions.

24. An apparatus as claimed in claim 21, further comprising:

means for removing said first voltage from said substance introducing means when said alternating voltage causes said ions to be trapped in said ion trapping field; and

means for applying a second voltage to said at least one end cap electrode after said removing means removes said first voltage from said ion introducing means.

30. An apparatus as claimed in claim 13 wherein said means for introducing directs ions created at a non-centered portion of said ion trapping field toward a center portion of said ion trapping field.

31. An apparatus as claimed in claim 30, further comprising means for applying a voltage to said at least one end cap electrode to reduce said initial kinetic energy of said each of said ions being introduced into said ion trapping field.

32. A method as claimed in claim 30, wherein said predetermined gradual rate is substantially linear.

33. A method as claimed in claim 31, wherein said predetermined gradual rate is substantially linear.

34. An apparatus as claimed in claim 31, further comprising means for removing said voltage from said at least one end cap electrode when said alternating voltage causes said ions to be trapped in said ion trapping field.