ICR ion trap

Details ICR ion trap ICR ion trap

1990-02-21

1991-01-01

Berman, Jack I.

Radiant energy

Ionic separation or analysis

Cyclically varying ion selecting field means

250281, 250282, H01J 4938

Patent

active

049820877

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to an ICR ion trap comprising electrically conductive side plates of equal axial length extending in parallel to one axis, and electrically conductive end plates extending perpendicularly to the said axis, closing the space defined by the said side plates and being electrically insulated from the latter, and a voltage source serving for applying trapping potentials to the side plates and end plates.
Ion traps of this kind have been used in ICR mass spectrometers and serve the purpose of trapping the ions of substances intended to be examined by mass spectroscopy, using the cyclotron resonance. For trapping negative ions, the end plates are in this case maintained at a negative potential, relative to the side plates, while for trapping positive ions the potential of the end plates must be positive relative to that of the side plates.
From the above it appears that with the known ICR ion traps the polarity of the potential of the end plates, relative to the side plates, determines the polarity of those ions that can be trapped by means of such an ion trap. If, as is usually the case, the ions are generated inside the ion trap by exposure of the substance to be examined to radiation, for example by application of a laser beam or an electron beam, then negative and positive ions may occur at the same time, in particular when an electron beam is applied, and of the two types of ions so obtained one will always be lost although it may absolutely be of interest to examine both types of ions. On the other hand, it may also be of interest to examine, by means of mass spectroscopy, any recombination reactions between positive and negative ions, but this the known ICR ion traps generally do not allow. Consequently, there exists a demand for ion traps which would permit to trap both positive and negative ions at the same time.


SUMMARY OF THE INVENTION

Now, it is the object of the present invention to provide an ion trap which enables positive and negative ions to be trapped at the same time.
This objective is achieved according to the invention by an ICR ion trap of the type described above wherein additional electrode plates arranged at a certain spacing from the said end plates extend in parallel to the latter and can be supplied, by means of the voltage source, with trapping potentials of a polarity opposite to the polarity of the potentials applied to the said end plates.
The ICR ion trap according to the invention, therefore, provides an arrangement where two areas forming ICR ion traps are sort of nested in each other. While the ions of the one polarity are trapped in the conventional manner between the end plates defining an inner area, the other ions are permitted to escape through holes provided in the end plates and to impinge upon the additional electrode plates defining an outer area. Having a polarity opposite to that of the end plates, the electrodes act to reflect these other ions and cause them to fly through the openings in the end plate and right to the other additional electrode plate where they are reflected again. Consequently, the ions having the other polarity are caused to traverse the inner area defined by the end plates and are permitted in this way to interact with the ions trapped within this area of the ion trap. Then recombination reactions, for example, may occur in this area the results of which may be studied subsequently by mass analysis of the ions trapped. Of course, there remains the fact that only negative or only positive ions can be detected at any time because only the ions trapped between the side plates, i.e. also between the end plates, can be excited to perform cyclotron movements so that they can be elimated selectively. However, there always exists the possibility to change the voltages following the analysis of the ions of the one polarity, so that the ions of the other polarity, or at least a considerable portion thereof, can be transferred into and trapped in the ICR ion trap for subsequent analysis.
There h

REFERENCES:
patent: 4588888 (1986-05-01), Ghaderi et al.
Giancaspro et al., International Journal of Mass Spectrometry, 72 (1986), Oct., No. 1/2, pp. 63-71.

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