Quadrupole trap improved technique for ion isolation
AssigneeVarian Associates, Inc.
InventorGregory J. Wells
Life of this patent
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Abstract
A method for isolating an ion in a QIT (1) employing values from a mass axis calibration chart to establish the maximum DAC value to scan to in order to scan out m(p)-1 and less during ramp up of RF trapping field while applying a specifically selected fixed supplemental frequency applied during said calibration; and employing values from the calibration curve to establish the DAC value to scan out m(p)+1 and greater during ramping down of RF trapping field, while applying a previously determined fixed broadband spectrum to the QIT end caps.
Claims17
In a method for isolating a selected parent ion having a mass m(p) for MS/MS spectroscopy employing a quadrupole ion trap (QIT) system, said QIT system having a ring electrode, a pair of end caps, an RF trapping voltage source having a trapping frequency F connected to said ring electrode, and supplementary RF voltage generator sources connected to said end caps, said method for isolating a selected parent ion including:
- (a) establishing said RF trapping voltage at a low value to enable retention of a large mass range of ions in said ion trap;
- (b) ionization of a sample in said QIT;
- (c) establishing said end caps at a zero DC voltage differential;
- (d) ramping up said RF trapping voltage to eject ions;
- (e) applying a broadband spectrum RF with a first supplementary RF generator to said end caps to resonantly reject those ions having masses greater than m(p);
- (f) reducing said RF trapping voltage to a value to trap daughter ions, if any, produced by disassociation of said parent ion;
- THE IMPROVED METHOD COMPRISING:
- applying a fixed frequency supplemental excitation to said end caps during at least a portion of the time of step (d).
In a method for isolating a selected parent ion having a mass m(p) for MS/MS spectroscopy employing a quadrupole ion trap (QIT) system, said QIT system having a ring electrode, a pair of end caps, an RF trapping voltage source having a trapping frequency F connected to said ring electrode, a first supplementary voltage generator source connected to said end caps, and a second supplementary voltage generator source connected to said end caps, said method for isolating a selected parent ion including:
- (a) establishing said RF trapping voltage at a low value to enable retention of a large mass range of ions in said ion trap;
- (b) ionization of a sample in said QIT;
- (c) establishing said end caps at a zero DC voltage differential;
- (d) ramping up said RF trapping voltage;
- (e) applying a broadband spectrum RF with said first supplementary RF generator to said end caps to resonantly reject those ions having masses greater than m(p);
- (f) reducing said RF trapping voltage to a value to trap daughter ions, if any, produced from disassociation of said parent ion;
- THE IMPROVED METHOD COMPRISING:
- said step of applying a broadband spectrum of RF to said end caps includes applying a predetermined, broadband spectrum of frequencies, said spectrum of frequencies including frequencies up to approximately one half of the RF trapping frequency F.
In a quadrupole ion trap system having a ring electrode, a pair of end caps, an RF trapping generator, first and second supplemental ion excitation generators, means to couple said first and second supplementary ion excitation generator sources to said end caps, and means coupling said RF trapping generator to said ring electrode,
- THE IMPROVEMENT COMPRISING:
- said first supplementary excitation source is a fixed frequency generator which fixed frequency of said fixed frequency generator is approximately (F/2) where F, is the frequency of said RF trapping generator.
In a QIT system having a ring electrode, an RF trapping generator, first and second supplemental ion excitation generators, means to couple said first and second supplemental ion excitation generators to said end caps, and means coupling said RF trapping generator to said ring electrode,
- THE IMPROVEMENT COMPRISING:
- said second supplemental excitation ion generator being a broadband frequency source having a frequency spectrum from 20 KHz to substantially (F/2), said spectrum comprised of equal amplitude, equally spaced frequencies having random phases, where F equals, in operation, the RF frequency of said RF trapping generator.
Dependencies are inferred from the claim text.