Triple quadrupole mass spectrometer with capability to perform multiple mass analysis steps
View Patent ↗A method of analyzing a substance comprises ionizing the substance to form a string of ions. The ions are then subject to a first mass analysis step. In one embodiment, the ions are accelerated into a collision cell in known manner to form primary fragment ions. These primary fragment ions are then accelerated into a downstream mass analyzer, to promote secondary fragmentation. In another embodiment of the invention, ions are passed through the collision cell, without fragmentation, and then accelerated from the collision cell into a low pressure section, which may be a mass analyzer or a rod set for collecting and collimating ions. This is done under conditions that promote fragmentation. The operating conditions of the low pressure section can be such as to promote collection or retention of ions depending upon their mass, and more specifically to reject low mass ions. This enables primary fragment ions to be cooled, and secondary fragment ions to be formed subsequently from these ions after they have disipated some of their energy. This enables control of secondary fragmentation processes, and offers numerous opportunities for analyzing complex ions.
1. A method of analyzing a substance, the method comprising:
(1) ionizing the substance to form a stream of ions;
(2) subjecting the ion stream to a first mass analysis, to select ions having a desired mass to charge ratio, as precursor ions;
(3) introducing the precursor ions into a collision cell to promote fragmentation of the precursor ions, thereby to generate primary fragment ions;
(4) in the collision cell, selecting primary fragment ions having a desired mass to charge ratio, and rejecting other ions;
(5) accelerating the selected primary fragment ions from the collision cell into a downstream linear ion trap mass analyzer, thereby to promote secondary fragmentation; and
(6) scanning ions out of the downstream linear ion trap mass analyzer by a radial ejection technique to generate a mass spectrum.
2. A method as claimed in claim 1 , wherein step ( 3 ) comprises accelerating the precursor ions into the collision cell, to promote fragmentation by collision with the gas.
3. A method as claimed in claim 1 , wherein selection of the primary fragment ions in step ( 4 ) comprises removing ions of a mass to charge ratio greater than the mass to charge ratio of the selected primary fragment ions and separately removing ions with a mass to charge ratio less than the mass to charge ratio of the selected primary fragment ion, the removal of the ions with mass to charge ratios higher and lower than the mass to charge ratio of the selected primary fragment ion being effected in either order.
4. A method as claimed in claim 3 , which includes effecting removal of primary fragment ions with mass to charge ratios greater and less than the mass to charge ratio of the selected primary fragment ion in the collision cell.
5. A method as claimed in claim 4 , which includes trapping the primary fragment ions and any residual precursor ions in the collision cell, during step ( 4 ).
6. A method as claimed in claims 1 , 2 , 3 , 4 or 5 , which includes effecting step ( 6 ) by scanning ions out of the downstream linear ion trap mass analyzer by an axial ejection technique.
7. A method of analyzing a substance, the method comprising:
(1) ionizing the substance to form a stream of ions;
(2) subjecting the ion stream to a first mass analysis, to select ions having a desired mass to charge ratio, as precursor ions;
(3) introducing the precursor ions into a collision cell to promote fragmentation of the precursor ions, thereby to generate primary fragment ions;
(4) in the collision cell, selecting primary fragment ions having a desired mass to charge ratio, and rejecting other ions by removing ions of a mass to charge ratio greater than the mass to charge ratio of the selected primary fragment ions and separately removing ions with a mass to charge ratio less than the mass to charge ratio of the selected primary fragment ion, the removal of the ions with mass to charge ratios higher and lower than the mass to charge ratio of the selected primary fragment ion being effected in either order;
(5) accelerating ions from the collision cell into a downstream mass analyzer, thereby to promote secondary fragmentation; and
(6) scanning ions out of the downstream mass analyzer by a radial ejection technique.
8. A method as claimed in claim 7 , wherein step ( 3 ) comprises accelerating the precursor ions into a collision cell, to promote fragmentation by collision with the gas.
9. A method of analyzing a substance, the method comprising:
(1) ionizing the substance to form a stream of ions;
(2) subjecting the ion stream to a first mass analysis, to select ions having a desired mass to charge ratio, as precursor ions;
(3) accelerating the precursor ions into a relatively high pressure section to promote fragmentation of the precursor ions, thereby to generate primary fragment ions;
(4) providing a multipole rod set in the high pressure section, for at least promoting collection and focusing of ions received therein, and providing at least an RF voltage to the multipole rod set to focus ions.
(5) trapping the ions in the multipole rod set, and scanning ions out radially from the multipole rod set to subject the fragment ions to a second mass analysis, to generate a mass spectrum.
10. A method as claimed in claim 9 , wherein ( 4 ) includes providing a quadrupole rod set as the multipole rod set, sod selling the q value of the quadrupole rod set to provide a high fill mass that is approximately that of the mass to charge ratio of a desired ion.
11. A method as claimed in claim 9 , which includes providing the RF voltage during the fill step such that the q value of low ions is greater than q=0.9, to at least delay capture by the multipole rod set of ions with a low mass to charge ratio.
12. A method as claimed in claim 11 , which includes selling the RF level to enhance sensitivity for ions of a desired mass to charge ratio.
13. A method as claimed in claim 11 , which includes: providing the elevated RF level as a first RF voltage for pre-determined delay time, to cause the primary fragment ions to dissipate energy by collision with the collision gas, and then lowering the RF level to a second, lower RF voltage whereby lower m/z ions can be trapped.
14. A method as claimed in claim 13 , which includes setting the delay time to reduce the energy of the primary fragment ions to a level sufficient to substantially suppress formation of secondary fragment ions, and subsequently reducing the RF level to the second, lower RF voltage for the second mass analysis of step ( 4 ).
15. A method as claimed in claims 11 , 12 , 13 or 14 which includes trapping ions in the multipole rod set and scanning ions out to effect the second mass analysis of step ( 4 ).
16. A method as claimed in claim 15 , which includes progressively increasing at least one of a RF voltage and an AC voltage applied to the multipole rod set, to scan ions out of the multipole rod set radially.
17. A method as claimed in claim 15 , which includes, after reducing the RF voltage to the second RF voltage, providing a cool time period, to enable any excess energy of the ions to dissipate by collision before effecting the second mass analysis of step ( 5 ), and effecting the second mass analysis by scanning ions out from the multipole rod set.
18. A method of analyzing a substance, the method comprising:
(1) ionizing the substance to form a stream of ions;
(2) subjecting the ion stream to a first mass analysis, to select ions having a desired mass to charge ratio, as precursor ions;
(3) introducing the precursor ions into a collision cell to promote fragmentation of the precursor ions, thereby to generate primary fragment ions;
(4) in the collision cell, selecting primary fragment ions having a desired mass to charge ratio, and rejecting other ions; and
(5) radially scanning ions out of the collision cell to generate a mass spectrum.
19. A method as claimed in claim 18 , wherein step ( 3 ) comprises accelerating the precursor ions into the collision cell, to promote fragmentation by collision with the gas.
20. A method as claimed in claim 18 or 19 , wherein selection of the primary fragment ions in step ( 4 ) comprises removing ions of a mass to charge ratio greater than the mass to charge ratio of the selected primary fragment ions and separately removing ions with a mass to charge ratio less than the mass to charge ratio of the selected primary fragment ion, the removal of the ions with mass to charge ratios higher and lower than the mass to charge ratio of the selected primary fragment ion being effected in either order.
21. A method as claimed in claim 20 , which includes effecting removal of primary fragment ions with mass to charge ratios greater and less than the mass to charge ratio of the selected primary fragment ion in the collision cell.
22. A method as claimed in claim 21 , which includes trapping the primary fragment ions and any residual precursor ions in the collision cell, during step ( 4 ).
23. A method as claimed in claim 18 or 19 , which includes effecting step ( 5 ) by axially scanning ions out of the collision cell.