Radiant energy – Ionic separation or analysis – Ion beam pulsing means with detector synchronizing means
Reexamination Certificate
1999-06-17
2001-08-14
Anderson, Bruce C. (Department: 2881)
Radiant energy
Ionic separation or analysis
Ion beam pulsing means with detector synchronizing means
C250S281000, C250S282000, C250S283000, C250S3960ML
Reexamination Certificate
active
06274866
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to mass spectrometry, and more particularly to time-of-flight mass spectrometry using an ion reflector.
BACKGROUND OF THE INVENTION
Mass spectrometry is a widely used analytical technique for studying molecular structures in organic chemistry and biochemistry. Mass spectrometry techniques involve the production of ionized species from a material sample and the analysis of the species based on their mass and charge. Typically, a spectrum is generated that illustrates the relative abundance of species as a function of their mass (or mass-to-charge (M/Z) ratios in cases when ions may have a charge of greater than 1).
One type of mass spectrometer used for analysis is a time-of-flight mass spectrometer (TOFMS). In a conventional time-of-flight mass spectrometer, the ionized species are accelerated to the same kinetic energy by a potential field, and then allowed to drift in a field free region before striking a detector. The ionized species separate by mass, within the field free region, because lighter ions travel to the detector faster than heavier ions. By detecting the relative amounts of ions at different “flight times”, a mass spectrum can be generated.
Tandem mass spectrometers (Tandem MS), including tandem time-of-flight mass spectrometers (Tandem TOFMS) have been developed to provide more information on the material being analyzed and, in particular, to permit improved discrimination between species that have similar mass-to-charge ratios. Typically, tandem MS techniques involve selecting only specific ions, having a particular mass-to-charge ratio, for analysis. The selected parent ions are then dissociated by introducing activation energy to form fragmented ions. The fragmented ions are analyzed to provide the information regarding the structures and origin of the parent molecule.
The following references and U.S. patents describe different mass spectrometry techniques.
Cooks (R. G. Cooks et al., Int. J. Mass Spectrom. Ion Processes. 100, p.209, 1990) discloses mass spectrometry techniques involving surface induced dissociation (SID) of parent ions. SID advantageously enables a high dissociation efficiency for large molecules.
A tandem TOFMS is described by Schey (K. L. Schey et al., Int. J. Mass Spectrom. Ion Processes. 77, p. 49, 1987) which employs a 45° stainless steel target for surface induced dissociation. Another tandem TOFMS is described by Williams (E. R. Williams et al., Int. J. Mass Spectrom. Ion Processes, 123, p. 233, 1993) in which an ion reflector is used as the dissociation target. Though both instruments demonstrated the ability to dissociate relatively large molecules up to mass 1,200 AMU, the instruments had a relatively low mass resolving power for fragment ions.
In U.S. Pat. No. 5,032,722, Boesl describes an MS/MS time-of-flight mass spectrometer. The spectrometer includes an ion source for generating a pulsed primary ion beam, a device for influencing the ions intermittently, in sharply defined areas, and an ion reflector for balancing out time-of-flight differences between ions of identical mass. The reflector includes a movable reflector end plate, which enables primary ions to be eliminated from the spectrum.
In U.S. Pat. No. 5,202,563, Cotter et al., describe a tandem time-of-flight mass spectrometer. The spectrometer incorporates two reflecting-type mass analyzers coupled via a collision chamber. The instrument uses specially designed flight channels that can be electrically floated with respect to the grounded vacuum housing. The design permits either pulsed extraction or constant field extraction of ions from the ionization source, in either low or high energy collisions in the collision chamber.
In U.S. Pat. No. 5,144,127, Williams et al., describes a tandem time-of-flight mass spectrometer that makes use of surface induced dissociation (SID). In one case, the SID surface can be maneuvered within the spectrometer.
Though the above-mentioned U.S. Patents and references describe mass spectrometers having a variety of different configurations, a need exists for a mass spectrometer that can operate in tandem mode to study detailed compositional information of a sample such as specific bond energies.
SUMMARY OF THE INVENTION
The invention provides mass spectrometer systems, including time-of-flight mass spectrometers, and methods of performing mass spectroscopy. The systems are capable of operating in tandem or conventional mode. When operating in tandem mode, the systems generate parent ions from a sample which are subsequently fragmented by a dissociation element to form fragmented ions. The systems include an ion reflector that, when operating in tandem mode, provides a discontinuous voltage to control the collision energy of the parent ions with the dissociation element and, in some embodiments, a second voltage that changes the energy of the fragmented ions. In preferred embodiments, the discontinuous voltage and the second voltage are applied as pulses.
In one aspect of the invention, a system for mass spectrometry is provided. The system includes an ion source capable of generating a plurality of parent ions from a sample. A portion of the parent ions follow a flight path. The system further includes an ion reflector constructed and arranged to receive the parent ions following the flight path and to apply a first, discontinuous voltage that changes the energy of the parent ions following the flight path. The system further includes a dissociation element positioned so that the parent ions, having an energy changed by the first, discontinuous voltage applied by the ion reflector, collide with the dissociation element thereby forming a plurality of fragmented ions. A portion of the fragmented ions continue to follow the flight path. The system further includes a detector positioned to detect the fragmented ions that follow the flight path.
In another aspect of the invention, the above-described system further includes electrical pulse circuitry electrically connected to the ion reflector and constructed and arranged to apply a first, discontinuous ion reflector voltage that changes the energy of the parent ions following the flight path.
In another aspect of the invention, another system for mass spectrometry is provided. The system includes an ion source capable of generating a plurality of parent ions from a sample. A portion of the parent ions follow a flight path. The system further includes an ion reflector constructed and arranged to receive the parent ions following the flight path and to apply a discontinuous voltage that changes the energy of the parent ions following the flight path. The system further includes a dissociation element positioned so that the parent ions, having an energy changed by the discontinuous voltage applied by the ion reflector, collide with the dissociation element thereby forming a plurality of fragmented ions. A portion of the fragmented ions continue to follow the flight path. The system further includes a second ion reflector constructed and arranged to receive the fragmented ions following the flight path and to apply a discontinuous voltage that changes the energy of the fragmented ions following the flight path. The system further includes a second dissociation element positioned so that the fragmented ions, having an energy changed by the discontinuous voltage applied by the second ion reflector, collide with the dissociation element thereby forming a plurality of second fragmented ions. A portion of the second fragmented ions continue to follow the flight path. The system further includes a detector positioned to detect the second fragmented ions that follow the flight path.
In another aspect of the invention, a method of mass spectrometry is provided. The method includes the step of generating a plurality of parent ions from a sample. The method further includes applying a first voltage that changes the energy of a portion of the parent ions following a flight path, and then turning the first voltage off. The method further includes fragmenting
Agilent Technologie,s Inc.
Anderson Bruce C.
Wells Nikita
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