Radiant energy – Ionic separation or analysis
Reexamination Certificate
2003-04-22
2004-12-07
Font, Frank G. (Department: 2881)
Radiant energy
Ionic separation or analysis
C250S282000, C250S283000, C250S288000, C250S291000, C250S306000
Reexamination Certificate
active
06828549
ABSTRACT:
FIELD OF INVENTION
The invention relates to a device and method for moving an ion source in a magnetic field by means of the Lorentz force.
BACKGROUND OF THE INVENTION
Electron impact ionization is a well-established and frequently used standard method for generating ions in mass spectrometers. Perhaps the most widely used electron emission device basically consists of a metal filament. An electrical current flowing through this filament makes it glow. By applying an electrical voltage, the electrons which leave the filament due to the thermionic emission are “extracted” and accelerated. If one of these electrons now collides with a neutral molecule with an ionization energy lower than the kinetic energy of the electron, then a positive ion is formed from this molecule (electron impact ionization). Thermal electrons, on the other hand, can produce negative ions from neutral molecules by a process of electron attachment or electron capture. During the formation of a positive ion, collisions with electrons which have a significantly higher kinetic energy than the ionization energy of the molecule leads to an increase of the internal energy of the molecular ion. This process usually ends with a fragmentation of the molecular ion. Therefore, fragment ion signals are also produced if electron impact ionization takes place at energies which are usually applied in mass spectrometry, typically 70 eV. This situation is often desirable since fragment-ion spectra provide valuable information about the structure of the molecule.
An additional fragmentation (dissociation) of ions is generally used in analytical mass spectrometry for determination of ionic structures since the generation of fragment ions (daughter ions) is directly related to the structure and chemical bonds of the ion to be fragmented. Consequently, the fragment spectrum is a characteristics of the parent ion (precursor) and represents a sort of ‘fingerprint’. Perhaps the most well known standard method of ion fragmentation in mass spectrometry relies on the acceleration of ions to be fragmented and their collision with the atoms or molecules of a collision-gas (collision-induced dissociation, collision-induced decomposition or CID). Collisions increase the internal energy of the ions, particularly the oscillation energy, enough to break weak chemical bonds. An overview of CID is provided in: Jennings, K. R. “The Changing Impact of the Collision-Induced Decomposition of Ions on Mass Spectrometry” Int.
J. Mass Spectrom
. 2000, 200, 479-493.
Another fragmentation method which is being increasingly used is the infrared multiphoton dissociation (IRMPD). In this case, an ion is excited by several, sequentially absorbed photons from an infrared laser (such as a CO
2
laser). Subsequently, dissociation products are observed which are similar to those produced by CID. For mass spectrometric methods which require very low pressures (ultra-high vacuum), IRMPD is a popular alternative since there is no need for collision gas to be introduced into the mass spectrometer for the ion fragmentation. By using CID or IRMPD, peptide or protein ions produce so-called b and y fragments, which are produced as a result of the cleavage of the bond between the peptide nitrogen atom and the neighboring carboxyl carbon atom. In order to use the infrared multiphoton dissociation, the IR laser beam and the ions must be brought to the same place. The interaction between the ions and the laser beam can best be achieved in an ion trap. An ion trap means here a Paul trap (RF ion trap or quadrupole trap), a Penning trap (ion-cyclotron resonance or ICR trap) or a linear RF multipole trap. The latter consists of a multipole ion guide device with two end electrodes (such as apertured end plates) to which a relatively low DC voltage is applied. If ions are to be stored in the trap, the voltages of the two apertured end plates are of the same polarity as the charge on the ions. The stored ions are extracted by reversing the polarity of the voltage at one of these end plates. For performing infrared multiphoton dissociation experiments of ions in one of these traps, an infrared laser beam is introduced, usually along the axis through the aperture of one of the terminal plates (terminal diaphragms in the case of a linear multipole trap or trapping plates in the case of an FT ICR (Fourier transform ion-cyclotron resonance) trap or end caps in the case of a Paul trap). The following represents some of the literature which deals with IRMPD applications. FT ICR mass spectrometry: Shi, S. D. H., Hendrickson, C. L., Marshall, A. G., Siegel, M. M., Kong, F. and Carter, G. T. “Structural Validation of Saccharomicins by High Resolution and High Mass Accuracy Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Infrared Multiphoton Dissociation Tandem Mass Spectrometry”
J. Am. Soc. Mass Spectrom
. 1999, 10, 1285-1290. Paul traps: Colorado, A., Shen, J. X., Vartanian, V. H. and 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
. 1996, 68, 4033-4043. Linear RF multipole traps: Hofstadler, S. A., Sannes-Lowery, K. A. and Griffey, R. A. “Infrared Multiphoton Dissociation in an External Ion Reservoir”
Anal. Chem
. 2000, 71, 2067-2070.
For many applications with stored ions Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS or FTMS for short) is popular because of its very high mass accuracy and mass resolution. As a consequence, all possible fragmentation methods are used in FTMS. A review of FT ICR mass spectrometry is provided in: Marshall, A. G., Hendrickson, C. L. and Jackson, G. S. “Fourier Transform Ion Cyclotron Mass Spectrometry: A Primer”
Mass Spectrom. Rev
. 1998, 17, 1-35.
Until now, fragmentation methods have been described which are either based on collisions between the molecular ions and the collision gas particles or on the interaction of ions with photons. A new fragmentation method introduced few years ago in the FT-ICR mass spectrometry relies on the interaction between electrons and ions. During this process multiply-charged positive ions capture low-energy electrons and produce cationic dissociation products. This process is referred to as electron capture dissociation or ECD. Multiply-charged positive ions can be produced by a method such as electrospray ionization. Electron capture dissociation of peptide or protein ions mostly produces c or z type fragment ions. These c or z fragment ions, which usually do not appear during CID or IRMPD processes, are formed as a result of the cleavage of the bond between the amino nitrogen atom participating in the peptide bond and the neighboring carbon atom from which the amino group originates. The c and z fragments produced by electron capture dissociation provide information which is complementary to that provided by IRMPD and CID, and consequently lead to a more complete mass-spectrometric sequence determination of polypeptides and proteins. The following literature is recommended for reading about the basis and applications of the ECD method: McLafferty, F. W., Horn, D. M., Breuker, K., Ge, Y., Lewis, M. A., Cerda, B., Zubarev, R. A. and Carpenter, B. K. “Electron Capture Dissociation of Gaseous Multiply Charged Ions by Fourier Transform Ion Cyclotron Resonance”
J. Am. Soc. Mass Spectrom
. 2001, 12, 245-149 and Zubarev, R. A., Horn, D. M., Fridriksson, E. K., Kelleher, N. L., Kruger, N. A., Lewis, M. A., Carpenter, B. K. and McLafferty, F. W. “Electron Capture Dissociation for Structural Characterization of Multiply Charged Protein Cations”
Anal. Chem
. 2000, 72, 563-573.
The efficiency of ECD primarily depends among others also on the number of electrons and their orbits in the trap. In FT ICR mass spectrometry, a filament produces electrons outside the ICR trap and axial to it. These are then guided into the trap parallel to the magnetic field. As for thermal conductivity reasons only the center of the filament heats up enough to generat
Baykut Gökhan
Schweikhard Lutz
Bruker Daltonik GmbH
El-Shammaa Mary
Font Frank G.
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