Mass spectrometer

Details Mass spectrometer Mass spectrometer

1998-01-05

2000-06-13

Anderson, Bruce C.

Radiant energy

Ionic separation or analysis

Cyclically varying ion selecting field means

250281, B01D 5944, H01J 4900

Patent

active

060752440

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a mass spectrometer realizing high sensitivity mass analysis by combining a linear ion trapping mass spectrometer and a linear mass filter.


BACKGROUND OF THE INVENTION

In radio frequency ion trap technology, a three-dimensional ion trapping using a radio frequency quadrupole field (so called Paul trap), and a linear ion trapping using a two-dimensional radio frequency quadrupole field and (a direct current voltage are known. This Paul trap comprises a ring electrode, and two end cap electrodes facing toward the hole in the ring. A radio frequency voltage is applied between the ring electrode and two end cap electrodes so as to generate a 3-dimensional radio frequency quadrupole electric field between the electrodes in which ions accumulate.
A description of this method of accumulating ions is given for example in H. G. Dehmelt, Adv.At.Mol.Phys. 3, 53 (1967).
As shown for example in U.S. Pat. No. 4,755,670 (1988), M. G. Raizen et al: Phys. Rev. A45, 6493 (1992), and J. D. Prestage et al: J. Appl. Phys. 66 1013 (1989), a linear quadrupole radio frequency electric field is generated in the vicinity of the center of the electrodes by applying a radio frequency electric field to the linear quadrupole electrode structure such that the electrodes on opposite sides have the same phase, and ions are thereby stably trapped in the direction perpendicular to the long axis of the electrodes. However, in this situation, ions leak from the ends of the electrodes. This is prevented by applying a direct current voltage having the same polarity of the trapped ions to the ends of the electrodes.
One field of application of ion trapping technology in industry is that of mass spectrometry. A mass spectrometer using a Paul trap, i.e. an ion trap mass spectrometer, is introduced in U.S. Pat. No. 2,939,952 invented by Paul et al in 1960. However, at that time an effective operation method for mass spectrometry was not given, and due to its low resolution and narrow mass range for mass analysis, it did not lead to its practical use as a mass spectrometer. When the operating method disclosed in U.S. Pat. No. 4,540,884, "mass selective instability", was invented, the device reached a practical level of mass range, detection sensitivity and detection resolution. However, mass spectrometry devices using linear ion trapping are not currently in practical use. A method of using these devices for mass spectrometry was suggested in U.S. Pat. No. 4,755,670 (1988). According to this method, the ions which accumulate in the trap are made to resonate in a mass-dependent oscillation mode, and the oscillation is detected electrically. Considering the induced signal strength, it may be expected that the sensitivity will be low. An example of a mass-analyzing function of a curved linear ion trap with an external ion detector is given by Waki et al in Physical Review Letters, Vol. 68, page 2007-2010 (1992), where the ion detector detects trapped ions that have been elected perpendicularly to the center axis of the trap after undesired ions are ejected using mass-selective instability. A similar configuration with other types of linear traps in combination with aforesaid techniques used in Paul traps is described by Bier et al in U.S. Pat. No. 5,420,425 (1995).
When one attempts to improve the sensitivity of the mass spectrometry device using the Paul trap which is now being put to practical use, an adverse effect appears due to background ions. In other words, the detection sensitivity of ions to be detected deteriorates when there is a large amount of background ions. This effect must therefore be removed. One method of doing this is the method of operating an ion trap mass spectrometer introduced, for example in U.S. Pat. No. 5,134,286. Therein it is proposed that background ions are mass-selectively ejected during injection of ions into the ion trap and in the stage prior to performing mass analyzing. However, according to this method, there are following disadvantages in removing the backgro

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