Methods and apparatus for reducing artifacts in mass spectrometers
First Claim
1. A method of operating a mass spectrometer having an elongate rod set which has an entrance end, a longitudinal axis, and an end distal of said entrance end, the method including:
- (a) admitting ions into said rod set via said entrance end;
(b) trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and a barrier field adjacent to said distal end;
(c) after trapping ions, establishing at least one additional barrier field in the interior of said rod set to define at least two compartments of trapped ions;
(d) ejecting at least some ions of a selected mass-to-charge ratio from selected, but not all, of said compartments; and
(e) detecting at least some of the ejected ions.
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Abstract
The invention solves the problem of artifact ghost peaks which can sometimes arise in mass spectrometers that employ a quadrupole rod set for both trapping and mass analyzing the trapped ions. The problem arises as a result of randomly distributed voltage gradients along the length of the rods. Three solutions are presented. The first approach involves improving the conduction characteristics of the rod sets. The second approach involves the application of at least one continuous axial DC field to the trapping quadrupole rod set in order to urge ions towards a pre-determined region of the trap, thereby avoiding voltage gradients. The third approach involves the application of one or more discrete axial fields to create one or more potential barriers along the axial dimension of the trap (in addition to the barriers used to initially trap the ions). These barriers prevent ions of differing voltage gradients from equilibrating with one another.
54 Citations
34 Claims
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1. A method of operating a mass spectrometer having an elongate rod set which has an entrance end, a longitudinal axis, and an end distal of said entrance end, the method including:
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(a) admitting ions into said rod set via said entrance end;
(b) trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and a barrier field adjacent to said distal end;
(c) after trapping ions, establishing at least one additional barrier field in the interior of said rod set to define at least two compartments of trapped ions;
(d) ejecting at least some ions of a selected mass-to-charge ratio from selected, but not all, of said compartments; and
(e) detecting at least some of the ejected ions. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A mass spectrometer, comprising:
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a multipole rod set, which defines a volume;
power supply means connected to said rod set for generating an RF field in said volume in order to constrain ions of a selected range of mass-to-charge ratios along first and second orthogonal dimensions;
means for introducing and trapping ions in said volume along a third dimension substantially orthogonal to said first and second dimensions;
means for defining at least two compartments of trapped ions; and
means for detecting ions from selected, but not all, of said compartments. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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21. In an ion trap which employs a two-dimensional RF field to constrain ions in two dimensions and at least one barrier potential to constrain ions in a direction substantially normal to said two dimensions, an improvement comprising:
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means for defining at least two compartments of trapped ions; and
means for ejecting and detecting ions from at least one, but not all, of the compartments. - View Dependent Claims (22)
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23. A method of operating a mass spectrometer having an elongate rod set which has an entrance end, a longitudinal axis, and an end distal to said entrance end, the method including:
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(a) admitting ions into said rod set via said entrance end;
(b) trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and by producing a barrier field adjacent said distal end;
(c) urging said trapped ions towards a pre-determined region of the volume defined by said rod set;
(d) ejecting at least some ions of a selected mass-to-charge ratio from the pre-determined region; and
(e) detecting at least some of the ejected ions. - View Dependent Claims (24, 25)
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26. A method of operating a mass spectrometer having an elongate rod set which has an entrance end, an exit end, and a longitudinal axis, the method including:
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(a) admitting ions into said rod set via said entrance end;
(b) trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and by producing a barrier field adjacent to said exit end;
(c) establishing a DC field along the longitudinal axis in order to urge ions towards said exit end;
(d) axially ejecting at least some ions of a selected mass-to-charge ratio; and
(e) detecting at least some of the ejected ions. - View Dependent Claims (27, 28)
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29. A method of operating a mass spectrometer having an elongate rod set which has an entrance end, a longitudinal axis, and an end distal of said entrance end, the method including:
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(a) admitting ions into said rod set via said entrance end;
(b) trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and by producing a barrier field adjacent to said distal end;
(c) establishing at least one DC field along said longitudinal axis in order to urge ions towards a pre-determined region along said longitudinal axis;
(d) ejecting at least some ions of a selected mass-to-charge ratio in a direction transverse to said longitudinal axis; and
(e) detecting at least some of the ejected ions. - View Dependent Claims (30, 31)
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32. A mass spectrometer, comprising:
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an elongate rod set which has an entrance end, a longitudinal axis, and an end distal to said entrance end, said rod set defining a volume;
means for admitting ions into said rod set via said entrance end;
means for trapping at least some of the ions introduced into said rod set by producing an RF field between the rods and by producing a barrier field adjacent said distal end;
means for establishing at least one DC field along said longitudinal axis in order to urge said trapped ions towards a pre-determined region of the volume defined by said rod set;
means for ejecting at least some ions of a selected mass-to-charge ratio from the pre-determined region; and
means for detecting at least some of the ejected ions. - View Dependent Claims (33, 34)
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Specification