Method of operating a mass spectrometer to provide resonant excitation ion transfer
View Patent ↗A method of operating a mass spectrometer having a rod set is provided. The rod set has a first end, a second end opposite to the first end, and a longitudinal axis extending between the first end and the second end. The method comprises a) admitting ions into the rod set; b) trapping at least some of the ions in the rod set by i) producing a first barrier field at a first end member adjacent to the first end of the rod set, ii) producing a second barrier field at a second end member adjacent to the second end of the rod set, and iii) providing an aggregate field comprising an RF field between the rods of the rod set; c) selecting a first selected mass to charge ratio of a first group of ions in the ions; d) determining a first excitement level of a selected characteristic of the aggregate field for the first group of ions; e) adjusting the selected characteristic of the aggregate field to the first excitement level to resonantly excite the first group of ions to mass selectively eject the first group of ions from the rod set past the barrier field; and, f) maintaining the selected characteristic of the aggregate field at the first excitement level during an excitement time interval wherein the excitation time interval is at least 1 millisecond.
1. A method of operating a mass spectrometer having a rod set, the rod set having a first end, a second end opposite to the first end, and a longitudinal axis extending between the first end and the second end, the method comprising:
a) admitting ions into the rod set;
b) trapping at least some of the ions in the rod set by i) producing a first barrier field at a first end member adjacent to the first end of the rod set, ii) producing a second barrier field at a second end member adjacent to the second end of the rod set, and iii) providing an aggregate field comprising an RF field between the rods of the rod set;
c) selecting a first selected mass to charge ratio of a first group of ions in the ions;
d) determining a first excitement level of a selected characteristic of the aggregate field for the first group of ions;
e) adjusting the selected characteristic of the aggregate field to the first excitement level to resonantly excite the first group of ions to mass selectively eject the first group of ions axially from the rod set past the barrier field; and,
f) maintaining the selected characteristic of the aggregate field at the first excitement level during an excitement time interval wherein the excitation time interval is at least 1 millisecond.
2. The method as defined in claim 1 wherein the selected characteristic is one of an amplitude and a frequency of the RF field.
3. The method as defined in claim 1 wherein the aggregate field comprises an excitation AC field, the selected characteristic being a frequency of the excitation AC field, and the excitation AC field being one of a dipole excitation voltage and a quadrupole excitation voltage.
4. The method as defined in claim 1 wherein the mass spectrometer further comprises a set of auxiliary electrodes, the excitation AC field being provided by the set of auxiliary electrodes.
5. The method as defined in claim 1 further comprising
selecting a second group of ions of a second selected mass to charge ratio from the ions;
determining a second excitement level of the selected characteristic of the aggregate field for the second group of ions; and,
after step f), adjusting the selected characteristic of the aggregate field to the second excitement level to resonantly excite the second group of ions to mass selectively eject the second group of ions axially from the rod set past the barrier field, and then
maintaining the selected characteristic of the aggregate field at the second excitement level during a second excitement time interval wherein the second excitation interval is at least 1 millisecond.
6. The method as defined in claim 5 wherein the step of adjusting the selected characteristic of the aggregate field to the second excitement level comprises adjusting the selected characteristic of the aggregate field from the first excitement level to the second excitement level in less than 1 millisecond.
7. The method as defined in claim 5 wherein the first group of ions differs by more than 1 amu from the second group of ions.
8. The method as defined in claim 7 wherein the selected characteristic is substantially constant over the excitation time interval and the second excitation time interval.
9. The method as defined in claim 1 wherein step b) comprises i) providing a first DC voltage difference between the first end member and the rod set to provide the first barrier field, and ii) providing a second DC voltage difference between the second end member and the rod set to provide the second barrier field.
10. The method as defined in claim 9 wherein the first DC voltage difference and the second DC voltage difference are equal.
11. The method as defined in claim 1 wherein step b) comprises i) providing a first AC voltage difference between the first end member and the rod set to provide the first barrier field, and ii) providing a second AC voltage difference between the second end member and the rod set to provide the second barrier field.
12. The method as defined in claim 11 wherein the first AC voltage difference and the second AC voltage difference are equal.
13. The method as defined in claim 1 wherein
step e) further comprises axially ejecting the first group of ions to a detector; and,
the method further comprises detecting at least some of the axially ejected first group of ions.
14. The method as defined in claim 1 wherein
step e) further comprises axially ejecting the first group of ions to a downstream ion trap; and,
the method further comprises g) further processing the first group of ions in the downstream ion trap.
15. The method as defined in claim 1 wherein
step e) further comprises axially ejecting the first group of ions to a downstream collision cell; and,
the method further comprises fragmenting the first group of ions in the collision cell and then axially ejecting the first group of ions to a downstream mass spectrometer for mass analysis.
16. The method as defined in claim 15 wherein the downstream mass spectrometer is a linear ion trap mass spectrometer, and the method further comprises storing the first group of ions in the linear ion trap mass spectrometer.
17. The method as defined in claim 15 wherein the downstream mass spectrometer is a time of flight mass spectrometer.
18. The method as defined in claim 5 , wherein at least one of the first excitation interval and the second excitation interval is at least 5 milliseconds.
19. The method as defined in claim 16 , wherein at least one of the first excitation interval and the second excitation interval is at least 20 milliseconds.
20. The method as defined in claim 1 further comprising storing a sample of ions upstream of the rod set; and, step a) comprises admitting a first batch of ions from the sample ions into the rod set.
21. The method as defined in claim 20 wherein
the sample ions are stored in a high pressure mass spectrometer operating at more than twice an operating pressure of the rod set, and
the method further comprises switching a barrier-generating member between the high pressure mass spectrometer and the rod set to an attractive mode during step a) to facilitate transfer of the first batch of ions from the high pressure mass spectrometer to the rod set, and to a repulsive mode during steps b) to f) to facilitate retaining the sample ions other than the first batch of ions in the high pressure mass spectrometer.
22. The method as defined in claim 21 wherein the high pressure mass spectrometer operates at more than ten times the operating pressure of the rod set.
23. The method as defined in claim 20 wherein the sample ions are stored in a MALDI source, and step a) comprises pulsing the MALDI source for a required number of times to fill the rod set.
24. The method as defined in claim 20 wherein the sample ions are stored in a nanospray source, and step a) comprises turning on the nanospray source to admit the first batch of ions into the rod set, and then turning off the nanospray source.
25. The method as defined in claim 20 wherein the sample ions are stored in an ion source upstream of the rod set, and step a) comprises turning on the ion source to admit the first batch of ions into the rod set, and then turning off the ion source.
26. The method as defined in claim 20 further comprising, after steps a) to f), admitting a second batch of ions from the sample ions stored in the high pressure mass spectrometer into the rod set.
27. The method as defined in claim 1 further comprising
detecting ions including the first group of ions ejected from the rod set;
generating a sequence of time peaks over the excitement time interval; and
selecting the first time peak in the sequence of time peaks as corresponding to the first group of ions.
28. The method as defined in claim 27 further comprising selecting a subsequent time peak in the sequence of time peaks as corresponding to an off-resonance group of ions different from the first group of ions.
29. A method of operating a mass spectrometer having a rod set, the rod set having a first end, a second end opposite to the first end, and a longitudinal axis extending between the first end and the second end, the method comprising:
a) admitting ions into the rod set;
b) trapping at least some of the ions in the rod set by i) producing a first barrier field at a first end member adjacent to the first end of the rod set, ii) producing a second barrier field at a second end member adjacent to the second end of the rod set, and iii) providing an aggregate field comprising an RF field between the rods of the rod set;
c) selecting a first selected mass to charge ratio of a first group of ions in the ions;
d) determining a first excitement level of a selected characteristic of the aggregate field for the first group of ions;
e) adjusting the selected characteristic of the aggregate field to the first excitement level to resonantly excite the first group of ions to mass selectively eject the first group of ions radially from the rod set past the barrier field; and,
f) maintaining the selected characteristic of the aggregate field at the first excitement level during an excitement time interval wherein the excitation time interval is at least 1 millisecond.
30. The method as defined in claim 29 wherein
step e) further comprises radially ejecting the first group of ions to a downstream collision cell; and,
the method further comprises fragmenting the first group of ions in the collision cell and then ejecting the first group of ions to a downstream mass spectrometer for mass analysis.
31. The method as defined in claim 30 wherein the downstream mass spectrometer is a time of flight mass spectrometer.