Spectrometer with axial field

• US 5,847,386 A
• Filed: 02/06/1997
• Issued: 12/08/1998
• Est. Priority Date: 08/11/1995
• Status: Expired due to Term

• Current Assignee: MDS Incorporated (Molecular Devices), Applied Biosystems Canada Limited (Thermo Fisher Scientific Incorporated)
• Original Assignee: MDS Incorporated (Molecular Devices)
• Inventors: Jolliffe, Charles L., Thomson, Bruce A.
• Primary Examiner(s): ANDERSON, BRUCE C
• Application Number:
  US08/796,582
• Time in Patent Office: 670 Days
• Field of Search: 250/281, 250/282, 250/288, 250/287, 250/292
• US Class Current: 250/288
• CPC Class Codes: H01J 49/005 by collision with gas, e.g. by introducing gas or by accelerating ions with an electric field
• CPC Class Codes: H01J 49/4225 Multipole linear ion traps, e.g. quadrupoles, hexapoles

Abstract

In a mass spectrometer, typically a quadrupole, one of the rod sets is constructed to create an axial field, e.g. a DC axial field, thereon. The axial field can be created by tapering the rods, or arranging the rods at angles with respect to each other, or segmenting the rods, or by providing a segmented case around the rods, or by providing resistively coated or segmented auxiliary rods, or by providing a set of conductive metal bands spaced along each rod with a resistive coating between the bands, or by forming each rod as a tube with a resistive exterior coating and a conductive inner coating, or by other appropriate methods. When the axial field is applied to Q0 in a tandem quadrupole set, it speeds passages of ions through Q0 and reduces delay caused by the need to refill Q0 with ions when jumping from low to high mass in Q1. When used as collision cell Q2, the axial field reduces the delay needed for daughter ions to drain out of Q2. The axial field can also be used to help dissociate ions in Q2, either by driving the ions forwardly against the collision gas, or by oscillating the ions axially within the collision cell.

Claims

1. In a spectrometer,

(a) a set of elongated rods having ends and defining an elongated volume therebetween, said volume having a longitudinal axis,

(b) a circuit for applying RF voltage to said elongated rods for said rods to transmit ions through said volume along said axis,

(c) said rods being tapered from one end to the other for establishing an axial electric field along at least a portion of said axis.

5. Apparatus according to claim 1, 3 or 4 wherein said rods form a quadrupole rod set.

6. Apparatus according to claim 1, 3 or 4 wherein said axial field is a DC field.

7. Apparatus according to claim 1, 3, or 4 wherein said axial field is a DC field, and including a collision gas within said volume for causing collisional cooling or fragmentation of ions within said volume.

2. In a spectrometer,

(a) a set of elongated rods having ends and defining an elongated volume therebetween, said volume having a longitudinal axis,

(b) a circuit for applying RF voltage to said elongated rods for said rods to transmit ions through said volume along said axis,

(c) at least some of said rods being oriented at an angle with respect to said axis for establishing an axial electric field along at least a portion of said axis.

3. In a spectrometer,

(a) a set of elongated rods having ends and defining an elongated volume therebetween, said volume having a longitudinal axis,

(b) a circuit for applying RF voltage to said elongated rods for said rods to transmit ions through said volume along said axis,

(c) each rod comprising a tube of insulating material having inner and outer surfaces, and means for establishing an axial electric field comprising a resistive material coating said outer surface, said tube having a coating of conductive material coating its inner surface for application of said RF thereto.

4. In a spectrometer,

(a) a set of elongated rods having ends and defining an elongated volume therebetween, said volume having a longitudinal axis,

(b) a circuit for applying RF voltage to said elongated rods for said rods to transmit ions through said volume along said axis,

(c) and means for establishing an axial electric field comprising auxiliary electrodes extending along at least a portion of the length of said rods, at least a portion of each of said auxiliary electrodes being sloped with respect to said axis.

8. In a spectrometer,

(a) a set of elongated members defining an elongated volume therebetween, said volume having a longitudinal axis,

(b) an ion source for injecting ions into said volume with an axial velocity,

(c) a circuit for applying RF voltage to said elongated members for said members to transmit ions through said volume along said axis,

(d) a Time-of-Flight drift tube connected to said members for receiving ions therefrom in a direction perpendicular to said axis,

(e) means for pulsing ions from said volume into said Time-of-Flight tube,

(f) and means extending along said members for establishing an axial electric field along at least a portion of said axis for reducing said axial velocity to approximately zero before operation of said means for pulsing ions into said drift tube.

9. In a spectrometer,

(a) a set of elongated members defining an elongated volume therebetween, said volume having a longitudinal axis, a radial dimension, and an exit end,

(b) an ion source for injecting ions into said volume,

(c) a gas source coupled to said volume for providing a drift gas in said volume for providing collisional cooling of ions in said volume,

(d) a circuit for applying RF voltage to said elongated members for said members to transmit ions through said volume along said axis.

(e) means extending along said members for establishing an axial electric field along at least a portion of said axis, said axial field applying a drift velocity to said ions for axial drifting of said ions in said volume at velocities dependent on their shape, mass and charge, thereby to provide separation of said ions in time at the exit end of said volume to provide separated groups of ions at said exit end, loss of said ions by diffusion in the radial dimension being reduced by collisions between said ions and said drift gas,

(f) and means operable for mass analyzing at least selected ones of said separated groups of ions, to improve the specificity of said spectrometer.

10. For use with an elongated set of conductive rods defining an elongated volume therebetween, said volume having a longitudinal axis, and a gas in said volume, a method of controlling fragmentation of ions in said volume comprising applying RF to said rods to control transmission of ions axially through said volume, establishing an axial electric field along at least a portion of said axis, and oscillating said axial electric field to cause fragmentation of ions in said volume.

11. A method according to claim 10 wherein said rods form a quadrupole rod set.

12. A method according to claim 11 wherein said axial electric field is a DC field.

13. For use with an elongated set of conductive members defining an elongated volume therebetween, said volume having a longitudinal axis, and an ion source for injecting ions into said volume with an axial velocity, a method of controlling passage of ions along said axis comprising applying RF to said elongated members to control transmission of ions axially through said volume, directing ions from said volume into a Time-of-Flight drift tube oriented at right angles to said axis, establishing an axial electric field along at least a portion of said axis, utilizing said axial electric field to reduce the axial velocity of said ions in said volume to approximately zero, and when said axial velocity has been reduced to approximately zero, then directing said ions into said Time-of-Flight drift tube.

14. A method according to claim 13 and including providing a gas within said volume.

15. For use with an elongated set of conductive members defining an elongated volume therebetween, said volume having a longitudinal axis, and a gas in said volume, a method of controlling fragmentation of ions in said volume comprising applying RF to said elongated members to control transmission of ions axially through said volume, and establishing an axial electric field along at least a portion of said axis, and controlling said axial field to drive said ions through said gas to dissociate ions in said volume.

16. For use with an elongated set of conductive members defining an elongated volume therebetween, said volume having a longitudinal axis and entrance and exit ends, and a drift gas in said volume, a method of providing mobility separation of ions in said volume comprising injecting ions into said entrance end of said volume, establishing an axial electric field along at least a portion of said axis to cause said ions to drift within said gas at velocities dependent on their mass to charge ratio while reducing diffusional loss of ions from said volume in the radial direction by collisional focussing in said gas, thereby producing separated groups of ions at said exit end, and mass analyzing desired ones of said separated groups of ions, thus to provide improved specificity to such mass analysis.

17. A method of mass analyzing a sample comprising:

(a) defining a volume between a set of elongated rods, said volume having an elongated axial dimension and a radial dimension,

(b) providing a damping gas in said volume,

(c) injecting into or forming ions of interest in said volume,

(d) applying potentials to said rods to contain ions in a mass range of interest in said volume,

(e) establishing an axial electric field along at least a portion of the length of said rods, and oscillating said field to dissociate ions contained in said volume,

(f) ejecting ions of interest from said volume for detection,

(g) and detecting at least some of the ejected ions for analysis.