Quadrupole with axial DC field

• US 6,111,250 A
• Filed: 10/21/1998
• Issued: 08/29/2000
• Est. Priority Date: 08/11/1995
• Status: Expired due to Term

• Current Assignee: MDS Incorporated (Molecular Devices), Applied Biosystems LLC (Thermo Fisher Scientific Incorporated)
• Original Assignee: MDS Health Group Limited
• Inventors: Thomson, Bruce A., Jolliffe, Charles L.
• Primary Examiner(s): Anderson, Bruce C.
• Application Number:
  US09/176,094
• Time in Patent Office: 678 Days
• Field of Search: 250/288, 250/292, 250/282
• US Class Current: 250/282
• 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. A method of mass analyzing a sample comprising:

(a) defining a volume between a set of elongated multipole rods, said volume having an elongated axial dimension and a radial dimension, and further including an entrance and an exit located on the axis,

(b) providing a collision gas in said volume,

(c) introducing ions at the entrance to the volume,

(d) applying an AC potential at least to said rods to confine ions in said volume for passage through the volume from the entrance to the exit,

(e) causing ions in said volume to fragment,

(f) rapidly varying said ions introduced at the entrance from first ions of a first mass to charge ratio to second ions of a second and different mass to charge ratio, and repeating such rapid variation,

(g) detecting ions leaving the exit of the volume, and providing a pause time of selected duration between detection of ions during supply of said first ions and detection of ions during supply of said second ions,

(h) and establishing an axial DC electric field in said volume to cause substantially all of said first ions in said volume during said pause time to exit said volume within said pause time.

2. A method as claimed in claim 1, wherein step (e) comprises providing ions from an upstream multipole rod set and rapidly varying a resolving potential applied to the upstream rod set, to effect a rapid switch from said first ions to said second ions.

3. A method of analyzing a sample comprising:

(a) isolating parent ions,

(b) fragmenting said parent ions in a volume defined by an elongated multipole rod set, to produce a set of fragment ions in said volume, said volume containing a collision gas to promote the formation of said fragments,

(c) injecting said fragment ions into a mass spectrometer following said multipole rod set, for analysis of said fragments,

(d) scanning said parent ions over a mass range, thereby producing a parent ion scan,

(e) establishing an axial field in said rod set to speed transmission of fragment ions therefrom into said following mass spectrometer whereby when the step of scanning the parent ions has moved from a previous parent ion to a subsequent parent ion, the time required for fragment ions from the previous parent ion to clear the volume and enter the following mass spectrometer will be reduced, thereby enabling faster scanning of a desired parent ion range, without loss of mass resolution or sensitivity.

4. A method of analyzing a sample comprising:

(a) injecting ions from an ion source into a first multipole elongated rod set defining a volume having a longitudinal axis, and applying an AC voltage to the rod set for transmitting first ions of interest through said volume,

(b) transmitting the first ions of interest from said first rod set into a following multipole rod set for further processing, to produce a first output ion measurement,

(c) rapidly changing the AC potential applied to said first multipole rod set from a first value to a second value to transmit second, ions of interest into said following multipole rod set for further processing, to produce a second output ion measurement,

(d) applying an axial D.C. electric field along at least a portion of said axis of the first multipole rod set to cause said second ions of interest from said source to rapidly refill said volume, to decrease the time required for said second ions in said volume to reach a steady state for said second output ion measurement.

5. A method according to claim 4 wherein a second voltage is applied to said following rod set, said first voltage being derived from said second voltage, and including the step of rapidly changing said second voltage between first and second values and thereby said first voltage, to cause said following rod set to transmit ions of low mass to charge ratio and then ions of a higher mass to charge ratio.

6. A method of improving the fragmentation efficiency of an RF multipole rod set, said rod set defining an elongated volume having a longitudinal axis and an exit, and a collision gas in said volume, said method comprising injecting ions into said volume with an axial velocity, and applying an axial electric field along said axis to increase the collision energy of said ions.

7. A method according to claim 6 and including the step of alternating said axial potential so that said ions are oscillated along said axis as they drift toward the exit of said volume, thereby increasing the number of collisions and the energy of collisions experienced by said ions.