Radiant energy – Ionic separation or analysis
Reexamination Certificate
2001-06-13
2004-06-01
Berman, Jack (Department: 2881)
Radiant energy
Ionic separation or analysis
C250S288000
Reexamination Certificate
active
06744040
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to means and method whereby ions from an ion source are selectively transmitted through a multipole apparatus having the capability of producing ion fragments via collisions with a surface or a gas to be readily analyzed by a TOF mass spectrometer. More specifically, a method and apparatus are described which use a plurality (preferrably three) of multipole devices, a collision surface (for SID), and/or a collision gas (for CID) to produce fragment ions of a selected m/z range for subsequent mass analysis.
BACKGROUND OF THE PRESENT INVENTION
The present invention relates to a multipole ion system with a collision surface for use in TOF mass spectrometry. The methods for transmitting ions and producing ion fragments described herein are enhancements of the techniques that are referred to in the literature relating to mass spectrometry.
Mass spectrometry is an important tool in the analysis of a wide range of chemical compounds. Specifically, mass spectrometers can be used to determine the molecular weight of sample compounds. The analysis of samples by mass spectrometry consists of three main steps—formation of gas phase ions from sample material, mass analysis of the ions to separate the ions from one another according to ion mass, and detection of the ions. A variety of means exist in the field of mass spectrometry to perform each of these three functions. The particular combination of means used in a given spectrometer determine the characteristics of that spectrometer.
To mass analyze ions, for example, one might use a magnetic (B) or electrostatic (E) analyzer. Ions passing through a magnetic or electrostatic field will follow a curved path. In a magnetic field the curvature of the path will be indicative of the momentum-to-charge ratio of the ion. In an electrostatic field, the curvature of the path will be indicative of the energy-to-charge ratio of the ion. If magnetic and electrostatic analyzers are used consecutively, then both the momentum-to-charge and energy-to-charge ratios of the ions will be known and the mass of the ion will thereby be determined. Other mass analyzers are the quadrupole (Q), the ion cyclotron resonance (ICR), the time-of-flight (TOF), and the quadrupole ion trap analyzers.
Before mass analysis can begin, however, gas phase ions must be formed from sample material. If the sample material is sufficiently volatile, ions may be formed by electron impact (EI) or chemical ionization (CI) of the gas phase sample molecules. For solid samples (e.g. semiconductors, or crystallized materials), ions can be formed by desorption and ionization of sample molecules by bombardment with high energy particles. Secondary ion mass spectrometry (SIMS), for example, uses keV ions to desorb and ionize sample material. In the SIMS process a large amount of energy is deposited in the analyte molecules. As a result, fragile molecules will be fragmented. This fragmentation is undesirable in that information regarding the original composition of the sample—e.g., the molecular weight of sample molecules—will be lost.
For more labile, fragile molecules, other ionization methods now exist. The plasma desorption (PD) technique was introduced by Macfarlane et al. in 1974 (Macfarlane, R. D.; Skowronski, R. P.; Torgerson, D. F.,
Biochem. Biophys. Res Commoun.
60 (1974) 616). Macfarlane et al. discovered that the impact of high energy (MeV) ions on a surface, like SIMS would cause desorption and ionization of small analyte molecules, however, unlike SIMS, the PD process results also in the desorption of larger, more labile species—e.g., insulin and other protein molecules.
Lasers have been used in a similar manner to induce desorption of biological or other labile molecules. See, for example, VanBreeman, R. B.: Snow, M.: Cotter, R. J., Int. J.
Mass Spectrom. Ion Phys.
49 (1983) 35; Tabet, J. C.; Cotter, R. J.,
Anal. Chem.
56 (1984) 1662; or Olthoff, J. K.; Lys, I.: Demirev, P.: Cotter, R. J.,
Anal. Instrument.
16 (1987) 93. Cotter et al. modified a CVC 2000 time-of-flight mass spectrometer for infrared laser desorption of involatile biomolecules, using a Tachisto (Needham, Mass.) model 215G pulsed carbon dioxide laser. The plasma or laser desorption and ionization of labile molecules relies on the deposition of little or no energy in the analyte molecules of interest. The use of lasers to desorb and ionize labile molecules intact was enhanced by the introduction of matrix assisted laser desorption ionization (MALDI) (Tanaka, K.; Waki, H.; Ido, Y.; Akita, S.; Yoshida, Y.; Yoshica, T.,
Rapid Commun. Mass Spectrom.
2 (1988) 151 and Karas, M.; Hillenkamp, F.,
Anal. Chem.
60 (1988) 2299). In the MALDI process, an analyte is dissolved in a solid, organic matrix. Laser light of a wavelength that is absorbed by the solid matrix but not by the analyte is used to excite the sample. Thus, the matrix is excited directly by the laser, and the excited matrix sublimes into the gas phase carrying with it the analyte molecules. The analyte molecules are then ionized by proton, electron, or cation transfer from the matrix molecules to the analyte molecules. This process, MALDI, is typically used in conjunction with time-of-flight mass spectrometry (TOFMS) and can be used to measure the molecular weights of proteins in excess of 100,000 daltons.
Time-of-flight mass spectrometry (or TOFMS) plays an important role in the analysis of chemical compounds. Specifically, TOF mass spectrometers are useful in determining the molecular weight of sample compounds. In orthogonal TOF mass spectrometers ions pass from the source into the analyzer in a direction which is orthogonal to the axis of the analyzer. The concept of orthogonal acceleration using TOFMS was disclosed by O'Hallran et al. in 1964 (G. J. O'Halloran et al.,
Determination of Chemical Species Prevalent in a Plasma Jet
. Technical Documentary Report No. ASD-TDR-62-664, prepared under contract AF 33(616)-8374 by the Bendix Corp. Research Laboratories (1964)). O'Hallran et al. also introduced the application of TOF mass analysis to ionization sources at elevated pressure. One advantage to using orthogonal acceleration and elevated pressure ionization sources is that ions form a continuous beam and can be mass analyzed more efficiently. Also, with the “orthogonal acceleration” method, the mass analysis occurs along an axis which is orthogonal to the ion's initial direction of motion. As a result, the initial energy of the ions does not significantly degrade the mass resolution of the instrument.
Chien and Lubman demonstrated the advantage of using a quadrupole ion trap—TOF mass analyzer in the analysis of electrospray produced ions (Chien, B. M.; Lubman, D. M.,
Anal. Chem.
66, 1630(1994)). The ions from the electrospray source are transferred with a high efficiency to the TOF analyzer and ions may be preselected and collision induced dissociation on these ions may be performed. One disadvantage with this method is low mass resolving power. Also, there are restrictions in the time required for cooling the ions and cycling the pressure in the ion trap.
Chernushevich et al discloses the use of ion introduction into an RF-quadrupole ion guide at a high gas pressure (I. V. Chernushevich, Proceedings of the 44th ASMS Conference of Mass Spectrometry and Allied Topics, May 12-16, 1173 (1996)). Similarly, Douglas discloses ion introduction into a quadrupole ion trap rather than a TOF analyzer (D. J. Douglas, U.S. Pat. No. 5,179,278). Here, the ions are cooled by passage through the quadrupole at elevated pressure and are then transferred into a low pressure region containing a quadrupole trap analyzer. This “collisional focusing” method has also been incorporated with the “orthogonal acceleration” method in TOF mass spectrometry to obtain a higher resolution mass spectrum.
Morris et al. discloses the use of additional multipole devices to preselect ions and induce collision dissociation in the trap—TOF analyzer (H. R. Morris et al.,
Rapid Comm. Mass S
Berman Jack
Bruker Daltonics Inc.
Ward & Olivo
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