Concentrating mass spectrometer ion guide, spectrometer and method
View Patent ↗An ion guide includes multiple stages. An electric field within each stage guides ions along a guide axis. Within each stage, amplitude and frequency, and resolving potential of the electric field may be independently varied. The geometry of the rods maintains a similarly shaped field from stage to stage, allowing efficient guidance of the ions along the axis. In particular, each rod segment of the i th of stage has a cross sectional radius r i , and a central axis located a distance R i +r i from the guide axis. The ratio r i /R i and is substantially constant along the guide axis, thereby preserving the shape of the field.
1. A method of guiding ions of selected m/z ratios within an ion guide along a guide axis, said method comprising:
providing a plurality of guide stages arranged along said guide axis;
within each of said plurality of guide stages, generating an alternating electric field that guides said ions along said guide axis, and confines ions of selected m/z ratios within a radius about said guide axis in each of said stages,
wherein the radius is sequentially reduced from stage to stage along said guide axis, and
wherein at least one of the amplitude and frequency of said electric field within each stage, varies from the amplitude, frequency, and axial and resolving potential within an adjacent stage.
2. The method of claim 1 , wherein said alternating electric field within each of said plurality of guide stages is a substantially quadrupolar electric field.
3. The method of claim 1 , wherein said alternating electric field within each of said plurality of guide stages is a substantially hexapolar electric field.
4. The method of claim 1 , wherein said alternating electric field within each of said plurality of guide stages is a substantially octopolar electric field.
5. The method of claim 1 , wherein said alternating electric field within each of said plurality of guide stages is a substantially n-polar electric field, with n>4.
6. The method of claim 1 , wherein said alternating electric field comprises first and second alternating components perpendicular to said guide axis.
7. The method of claim 1 , further comprising generating an electric field in a direction parallel to said guide axis to guide ions from stage to stage.
8. The method of claim 7 , wherein said electric field in a direction parallel to said guide axis spatially separates ions of different mass to charge ratios along said guide axis.
9. The method of claim 1 further comprising generating an electric field along said axis that prevent release of ions from said guide at a first time to, and releases ions from said guide at a second time.
10. The method of claim 1 , further comprising generating a second alternating electric field in a direction perpendicular to said guide axis to excite ions of particular selected m/z ratio.