Introduction of samples into an ion mobility spectrometer

Details Introduction of samples into an ion mobility spectrometer Introduction of samples into an ion mobility spectrometer

1994-01-24

1996-11-12

Berman, Jack I.

Radiant energy

Ionic separation or analysis

250288, H01J 4940

Patent

active

055742777

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTIONS

The present invention relates to ion mobility spectrometers (IMS's) and more particularly to a method and apparatus for introducing the effluent from a gas chromatograph into an ion mobility spectrometer.
The use of an ion mobility spectrometer in combination with a gas chromatograph employing, for example, a capillary on a packed separating column, is a well established technique.


SUMMARY OF THE INVENTION

FIG. 1 of the drawings attached show diagrammatically such a combination and the various gas flows in prior art equipment of this type.
An ion mobility spectrometer with an ionising source 10, a gating grid or grids 12, drift field electrodes 14 and a collector electrode 16, is linked with the outlet 18 of, for example, a capillary column gas chromatograph (not shown).
Time separated components of a sample introduced into the gas chromatograph appear at the outlet 18, are fed, together with the gas chromatograph carrier gas flow, into the ion mobility spectrometer in the region of the source 10, and are ionised. Sample ions and any unionised molecules are swept by the source gas flow 20, introduced through a port 22, into the region of the gating grids 12, which permit ions to enter the drift tube 13. Ions not passed by the grids 12, together with un-ionised molecules and chromatograph carrier gas, are swept out of the gating grid region through the exhaust vent 24.
Ions entering the drift tube 13 pass to the collector electrode 16 through the electric field set up by the electrodes 14, against the flow of the drift gas 26, introduced through a port 28, which sweeps out via the exhaust vent 24 any ions failing to reach the collector electrode 16.
The time of arrival of ions at the collector 16 is indicative of the identity of their parent molecules and the magnitude of the collector current flow produced by any group of ions is an indication of the amount of that component present in original sample introduced into the gas chromatograph.
In certain applications it has been found advantageous to provide the ion mobility spectrometer with a common unidirectional drift and source gas flow in order that all gas flows in the spectrometer may be vented at the inlet end downstream of the ionising source 10. This has been found to have the effect of seriously impairing the sensitivity of the ion mobility spectrometer, possibly as a result of the incoming separated samples from the chromatograph being at least in part swept out of the source region prior to ionisation.
It is an object of the present invention to overcome or mitigate this reduction in sensitivity in an ion mobility spectrometer employing an inlet end exhaust venting arrangement with a unidirectional drift and source gas flow.
In order to achieve the object of the invention means are provided to prevent or minimise removal of the gas chromatograph effluent from the source region of the ion mobility spectrometer prior to ionisation.
According to one aspect of the invention, the effluent from the gas chromatograph is introduced together with a further gas flow into the ion mobility spectrometer in the region of the ionising source, in a direction counter to the flow of the drift and source gas.
According to a second aspect there is provided an ion mobility spectrometer having a unidirectional drift and source flow which is exhausted downstream of an ionisation source, and means for introducing into the spectrometer in the region of the ionisation source the effluent from a gas chromatograph together with a further gas flow, the effluent and the further gas flow being introduced in a direction counter to the said unidirectional drift and source flow.
The effluent and the further gas flow may be introduced into the ion mobility spectrometer with either one wholly or partly surrounding the other.
Preferably the effluent from the gas chromatograph is wholly or partly surrounded by the further gas flow.
For example the outlet from the gas chromatograph may be surrounded by a conduit through which the further gas flow passe

REFERENCES:
patent: 4551624 (1985-11-01), Spangler et al.
patent: 5021654 (1991-06-01), Campbell et al.
patent: 5283199 (1994-02-01), Bacon, Jr. et al.

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