Radiant energy – Ionic separation or analysis – Cyclically varying ion selecting field means
Reexamination Certificate
2003-03-26
2004-10-12
Wells, Nikita (Department: 2881)
Radiant energy
Ionic separation or analysis
Cyclically varying ion selecting field means
C250S290000, C250S282000, C250S281000, C250S42300F, C250S424000, C250S50400H
Reexamination Certificate
active
06803569
ABSTRACT:
FIELD OF INVENTION
The invention relates generally to ion cyclotron resonance trap mass spectrometry and, more particularly, to the irradiation of ions in an ion cyclotron resonance trap.
BACKGROUND OF THE INVENTION
Due to its very high mass accuracy and mass resolution, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) has a unique place in ion-trap mass spectrometry. FT-ICR-MS uses electromagnetic ion traps. In a magnetic field, all ions with a component of motion perpendicular to the magnetic field lines are forced by the Lorentz force to describe cyclotron orbits. Without absorbing additional energy, they are unable to escape in the plane perpendicular to the magnetic field. However, a motion of ions along the magnetic field lines does not cause a Lorentz force, thus, the ions must be trapped in this dimension with an additional electric field. The ion detection is made here by determination of cyclotron frequencies of ions based on image currents in the trap. Since those frequencies are inversely proportional to the m/z ratio (mass divided by the number of charges) of the circling ions, the frequency determination means the determination of the m/z ratio. Nowadays, in analytical FT-ICR-MS generally strong superconducting magnets are used. The FT-ICR mass spectrometry has been reviewed by Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. “Fourier Transform Ion Cyclotron Resonance Mass Spectrometry: A primer”
Mass Spectrom. Rev.
1998, 17, 1-35.
Electron capture dissociation (ECD) is a relatively new method to fragment ions and to obtain insight into the ion structures using the information from fragment ion spectra. During the ECD process multiply charged ions in an ICR trap capture low energy electrons to produce cationic dissociation products. Multiply charged ions can be generated for example by electrospray ionization. The electron capture dissociation of peptide or protein ions mainly results in c and z type fragment ions. These c and z fragments, which are usually not formed in collision induced dissociation processes (CID, see below), are produced by cleaving the bond between the amino-nitrogen atom, which is involved in the peptide bond, and the neighboring carbon atom from which the amino group originates. The c and z fragments from ECD provide sets of information complementary to those from fragmentation by other ion-fragmentation methods and lead to a more complete determination of the sequences of polypeptides and proteins. The following literature is recommended about the fundamentals and applications of the ECD method: McLafferty, F. W.; Horn, D. M.; Breuker, K.; Ge, Y.; Lewis, M. A.; Cerda, B.; Zubarev, R. A.; Carpenter, B. K. “Electron Capture Dissociation of Gaseous Multiply Charged Ions by Fourier Transform Ion Cyclotron Resonance”
J. Am. Soc. Mass Spectrom.
2001, 12, 245-249. Zubarev, R. A.; Horn, D. M.; Fridriksson, E. K.; Kelleher, N. L.; Kruger N. A.; Lewis, M. A.; Carpenter, B. K.; McLafferty, F. W. “Electron Capture Dissociation for Structural Characterization of Multiply Charged Protein Cations”
Anal. Chem.
2000, 72, 563-573.
Dissociation processes resulting from electron-ion interactions are not limited to ECD. For characterization of negatively charged ions, the electron detachment dissociation (EDD) is used. In the EDD process, an electron is removed from multiply charged ions, while anionic dissociation products are formed (Budnik, B. A.; Haselman, K. F.; Zubarev, R. A. “Electron Detachment Dissociation of Peptide Di-Anions: An Electron-Hole Recombination Phenomenon”
Chem. Phys. Lett.
2001, 342, 299-302).
The efficiency and rate of ECD is dependent on the electron flux density. The efficiency and rate of ECD can be improved by maximizing the overlap of ions with the electron beam. In conventional FT-ICR mass spectrometry, electrons are generated by a filament, which is placed outside the ICR trap. In most cases, the filament is in the vicinity of the trap and still in the room-temperature bore of the superconducting magnet. Electrons are guided parallel to the magnetic field (axially) into the trap. Due to reasons of thermal conductivity, only a central region of a filament reaches a suitably high temperature and emits electrons. Therefore, the electron beam is usually very thin like a thread in the magnetic field. After the electron beam is formed, attempts to expand this thin beam fail, since every movement perpendicular to the magnetic field produces a Lorenz force at right angles to it, which drives the electrons into tiny cyclotron trajectories. The electron beam must therefore be generated as a wider beam initially. Recently, large-surface electron emitters have been used to produce electrons for the ECD experiments. This way, the electron emitting area has been dramatically increased and the probability of ion-electron interactions in the ICR trap leading to dissociation is increased. In fact, by using these new emitters, improved ECD results have been obtained (Tsybin, Y. O.; Hakansson, P.; Budnik, B. A.; Haselmann, K. F.; Kjeldsen, F.; Gorshkov, M.; Zubarev, R. A.; “Improved Low Energy Electron Injection Systems for High Rate Electron Capture Dissociation in Fourier Transform Ion Cyclotron Resonance Mass Spectrometry”
Rapid Commun. Mass Spectrom.
2001, 15, 1840-1854; as well as the world patent application WO 02/078048 A1 published in October 2002.).
In FT-ICR MS, one would like to study the interaction of stored ions with photons as well. It is possible to irradiate and excite ions with photons. As a result of this excitation ions can be fragmented too (photodissociation). The photons can be generated from ultraviolet, visible or infrared light, which may also be a laser beam.
A photo-induced fragmentation method which is increasingly used in FT-ICR mass spectrometry is infrared multiphoton dissociation (IRMPD). In this case, the ions are excited by multiple, sequentially absorbed infrared photons produced by an infrared laser (e.g. a CO
2
laser). Subsequently, a dissociation process is observed which produces similar results to the widely used collision induced dissociation (CID) method. For mass spectrometric methods such as FT-ICR, which require a very good ultra-high vacuum, IRMPD is a popular alternative since, in this case, no collision gas has to be “pulsed in” to fragment the ions. Similar to the CID, the so-called b- and y-type fragment ions from peptide or protein ions are also produced in IRMPD experiments. These ions are obtained by a cleavage of the bond between the peptide nitrogen atom and the (neighboring) carboxyl carbon atom. IRMPD is not only used in sequencing polypeptides and proteins, it is also generally used to investigate the higher order structures of biomolecules and their dynamics. When using the infrared laser to obtain a dissociation spectrum which will allow an identification of a substance, the irradiation time is generally less than 500 ms in FT-ICR mass spectrometry. In order to induce an infrared multiphoton dissociation, the IR laser beam must be introduced into a region where the ions are present. The interaction of ions with the laser beam can best be studied in an ion trap (Paul trap, Penning trap, ion cyclotron trap or linear RF multipole trap). For infrared multiphoton dissociation experiments in one of these traps, an infrared laser beam is introduced, usually axially to the trap and in most cases through the aperture of one of the end plates (end plates in the linear multipole trap, trapping plates in the FT-ICR trap or end caps in the Paul trap). Examples of literature which deals with the use of IRMPD applications are: Little, D. P.; Speir, J. P.; Senko, M. W.; O'Connor, P. B.; McLafferty, F. W. “Infrared Multiphoton Dissociation of Large Multiply-charged Ions for Biomolecule Sequencing”
Anal. Chem.
1994, 66, 2809-2815; Colorado, A.; Shen, J. X.; Vartanian, V. H.; Brodbelt J. “Use of Infrared Multiphoton Photodissociation with SWIFT for Electrospray Ionization and Laser Desorption Applications in a Quadrupole Ion Trap Mass Spectrometer”
Anal Chem.
Baykut Gökhan
Tsybin Youri O.
Bruker Daltonik GmbH
Wells Nikita
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