Two-Dimensional Radial-Ejection Ion Trap Operable as a Quadrupole Mass Filter
AssigneeThermo Funnigan LLC
InventorJae C. SCHWARTZ
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Abstract
A two-dimensional radial-ejection ion trap is constructed from four apertured electrodes having inwardly facing hyberbolic surfaces, with each electrode being spaced from the centerline by a distance r that is greater than the hyperbolic radius r0 defined by the hyperbolic surfaces. This geometry produces a balanced symmetrical trapping field that has a negligible octopole field component and a relatively large dodecapole or icosapolar field component. In one specific implementation, the ion trap is selectably operable as a quadrupole mass filter by applying a filtering DC voltage to the electrodes.
Claims26
A two-dimensional ion trap mass analyzer, comprising:
- four elongated rod electrodes each having a hyperbolic surface of hyperbolic radius r0 facing a centerline and an aperture extending through the thickness of the electrode;
- the four rod electrodes being equally spaced from the centerline by a distance r, wherein r is greater than the hyperbolic radius r0;
- and
- an RF voltage source for applying an RF trapping voltage to the rod electrodes to generate an RF trapping field that radially confines ions to the interior of the ion trap;
- and
- a DC voltage source for applying DC offsets to the rod electrodes or a set of axial trapping electrodes positioned outward of the rod electrodes to generate a potential well that axially confines ions within the interior of the ion trap.
A mass spectrometer, comprising:
- an ion source for generating ions from a sample to be analyzed;
- at least one ion optic for guiding the ions produced by the ion source;
- and
- a two-dimensional ion trap mass analyzer positioned to receive ions from the at least one ion optic, the ion trap mass analyzer comprising:
- a first ion trap structure including four elongated rod electrodes each having a hyperbolic surface of hyperbolic radius r0 facing a centerline and an aperture extending through the thickness of the electrode;
- the four rod electrodes being equally spaced from the centerline by a distance r, wherein r is greater than the hyperbolic radius r0;
- an RF voltage source for applying an RF trapping voltage to the rod electrodes to generate an RF trapping field that radially confined ions to the interior of the ion trap;
- and
- a DC voltage source for applying DC offsets to the rod electrodes or a set of axial trapping electrodes positioned outward of the rod electrodes to generate a potential well that axially confines ions within the interior of the ion trap.
A multipole structure for connection to an RF voltage source, comprising:
- four elongated rod electrodes arranged about a centerline of the multipole, each of the elongated electrodes having a curved surface facing an interior of the trap and a longitudinally extending aperture or recess;
- the electrodes being spaced from the centerline by a distance r such that, when opposite phases of an RF voltage are applied to opposed pairs of the electrodes, the resultant RF field has an octopolar component of not more than 0.001%.
A two-dimensional ion trap mass analyzer, comprising:
- four elongated rod electrodes each having a hyperbolic surface of a hyperbolic radius r0 facing a centerline, the rod electrodes being arranged into first and second opposed electrode pairs;
- the electrodes of the first electrode pair being adapted with apertures permitting the ejection of ions therethrough, and the electrodes of the second electrode pair being adapted with recesses that do not extend through the full thicknesses of the electrodes;
- the four rod electrodes being equally spaced from the centerline by a distance r, wherein r is greater than the hyperbolic radius r0;
- and
- an RF voltage source for applying an RF trapping voltage to the rod electrodes to generate an RF trapping field that radially confines ions to the interior of the ion trap;
- and
- a DC voltage source for applying DC offsets to the rod electrodes or a set of axial trapping electrodes positioned outward of the rod electrodes to generate a potential well that axially confines ions within the interior of the ion trap.
Dependencies are inferred from the claim text.