ION MOBILITY SPECTROMETER

Abstract

The invention relates to an ion mobility spectrometer (1) having an ionization chamber (13), with at least one ionization source (3) and at least one drift chamber (14) arranged downstream of the ionization chamber (13) in a desired drift direction (D) of the ions, wherein the ionization chamber (13) is connected to a feed duct (4) through which a sample gas to be analysed can be fed into the ionization chamber (13), characterized in that the ion mobility spectrometer (1) has a discharge duct (5) separate from the feed duct (4), which discharge duct is connected to the ionization chamber (13) and through which the sample gas can be discharged from the ionization chamber (13), wherein a) the ion mobility spectrometer (1) is configured to operate the ionization chamber (13) substantially field-free, at least during an ionization phase, and, in an injection phase, to move ions by means of an electric field out of the ionization chamber (13) into the drift chamber (14) and/or b) the ionization source (3) is designed as a pulse-controlled ionization source.

Claims

1. An ion mobility spectrometer, comprising: an ionization chamber comprising at least one ionization source and at least one drift chamber, wherein the at least one drift chamber is downstream of the ionization chamber in a drift direction of the ions, a feed channel connected to the ionization chamber through which a sample gas to be analyzed is fed to the ionization chamber, a discharge channel that is separate from the feed channel and is connected to the ionization chamber, wherein the sample gas is dischargeable from the ionization chamber through the discharge channel, wherein a) the ion mobility spectrometer is configured so that the ionization chamber is operated essentially without field at least during an ionization phase, and during an injection phase ions are moved out of the ionization chamber into the drift chamber by an electric field and/or b) the at least one ionization source is designed to be operated in a pulsed manner.

2. The ion mobility spectrometer as claimed in claim 1, wherein the feed channel and/or the discharge channel open directly into the ionization chamber.

3. The ion mobility spectrometer as claimed in claim 1 wherein an arrangement of the feed channel and of the discharge channel provides a flow direction of the sample gas which extends orthogonally to the drift direction of the ions through the drift chamber.

4. The ion mobility spectrometer as claimed in claim 1 wherein the discharge channel is connected to a surrounding atmosphere or to a suction device.

5. The ion mobility spectrometer as claimed in claim 1 wherein the feed channel is connected to a surrounding atmosphere or to an inlet system.

6. The ion mobility spectrometer as claimed in claim 1 wherein the feed channel and/or the discharge channel comprises an interior wall of an inert material or with an inert coating.

7. The ion mobility spectrometer as claimed in claim 1 wherein the at least one ionization source a) is arranged inside the ionization chamber or at least partially forms at least one wall of the ionization chamber and/or b) is arranged outside the ionization chamber and is connected to the ionization chamber via an ionization channel that opens into the ionization chamber.

8. The ion mobility spectrometer as claimed in claim 1 further comprising at least one ion gate in a form of a field switching shutter.

9. The ion mobility spectrometer as claimed in claim 1 wherein a central axis of the feed channel is essentially collinear with a central axis of the discharge channel.

10. The ion mobility spectrometer as claimed in claim 1 wherein the feed channel is connected from a mouth of the feed channel in the ionization chamber via a connecting channel formed in the ionization chamber to a mouth of the discharge channel in the ionization chamber, wherein the connecting channel is designed as a laminar flow body.

11. The ion mobility spectrometer as claimed in claim 10, wherein a cross-sectional area of the connecting channel differs from a cross-sectional area of the feed channel and/or of the discharge channel by less than ±50%.

12. The ion mobility spectrometer as claimed in claim 1 wherein the feed channel and/or the discharge channel has an essentially square, circular, rectangular or elliptical cross-section.

13. The ion mobility spectrometer as claimed in claim 1 wherein a width of the feed channel and/or of the discharge channel is at least 10% of an internal diameter of the drift chamber.

14. The ion mobility spectrometer as claimed in claim 1 wherein a depth of the feed channel and/or of the discharge channel is at least 10% of a depth of the ionization chamber.

15. The ion mobility spectrometer as claimed in claim 1 wherein a width of the feed channel and/or of the discharge channel differs from a diameter of the ion detector of the ion mobility spectrometer by less than ±50%.

16. The ion mobility spectrometer as claimed in claim 1 wherein a width of the feed channel and/or of the discharge channel differs from a diameter of an axially mounted ionization source of the at least one ionization source of the ion mobility spectrometer by less than ±50%.

17. The ion mobility spectrometer as claimed in claim 1 wherein a cross-sectional area of the discharge channel differs from a cross-sectional area of the feed channel by less than ±50%.

18. The ion mobility spectrometer as claimed in claim 1 further comprising a drift gas outlet channel through which drift gas fed into the drift chamber is dischargeable, wherein the drift gas outlet channel is constructed separately from the discharge channel.

19. The ion mobility spectrometer as claimed in claim 18 wherein the drift gas outlet channel opens directly into the drift chamber.

Description

[0043] The invention is explained in more detail below with reference to exemplary embodiments and making use of drawings. Here

[0044] FIG. 1 shows a schematic illustration of an ion mobility spectrometer, and

[0045] FIG. 2 shows a sectional illustration through the ion mobility spectrometer according to FIG. 1 along the cut plane A-A, and

[0046] FIGS. 3 to 7 show further cross-sectional illustrations of embodiments of the ion mobility spectrometer in the cut plane A-A.

[0047] FIG. 1 shows an ion mobility spectrometer 1 with a housing 2. An ionization chamber 13 and a drift chamber 14 are present in the housing 2. The ion mobility spectrometer 1 comprises an ion gate 10 in the region of the ionization chamber 13, for example in the form of a field switching shutter with an injection electrode 12 and a counter electrode 11. The ionization chamber 13 is then arranged between the injection electrode 12 and the counter electrode 11. The ionization source 3 can, moreover, also simultaneously constitute the counter electrode 11. The drift chamber 14 follows the ionization chamber 13 or the injection electrode 12 in a desired drift direction D of the ions. The drift chamber 14 ends at an ion detector 16. A field generation device 15 is present in the region of the drift chamber 14, for example in the form of annular electrodes surrounding the drift chamber 14. An electric field can be generated in the drift chamber 14 by the field generation device 15, exercising the desired drift effect on the ions under examination, so that these are transported from the ion gate 10 to the ion detector 16.

[0048] The ion mobility spectrometer 1 also comprises an ionization source 3 through which ions are made available in the ionization chamber 13. The ionization chamber 13 is connected to a feed channel 4 leading through the housing 2 and a discharge channel 5 also leading through the housing 2. The feed channel 4 serves to supply sample gas to the ionization chamber 13, and the discharge channel 5 to remove sample gas from the ionization chamber 13. A flow of sample gas can be generated in this way through the ionization chamber 13 from the feed channel 4 to the discharge channel 5. As can be seen, the discharge channel 5 is constructed separately from the feed channel 4.

[0049] A flow of drift gas can also be guided through the drift chamber 14. The drift chamber 14 comprises a drift gas inlet channel 17 and a drift gas outlet channel 18 for this purpose. The drift gas is thus guided to the drift gas outlet channel 18 in the direction opposite to the drift direction D. As can be seen, the drift gas outlet channel 18 is constructed separately from the discharge channel 5 and from the feed channel 4.

[0050] FIG. 2 shows a cross-sectional illustration of the ion mobility spectrometer 1 in the region of the ionization chamber 13 (corresponding to the cut plane A-A). It can be seen that the sample gas can be introduced through the feed channel 4 into the ionization chamber 13, and can be removed again through the discharge channel 5. The feed channel 4 is connected to the discharge channel 5 via a connecting channel 6 inside the ionization chamber 13. It is advantageous here if the width B of the feed channel 4 corresponds approximately to the width of the discharge channel 5, or at least does not differ from it greatly. It is furthermore advantageous to give the feed channel 4 and/or the discharge channel 5 a relatively large width B, corresponding for example to the diameter of the ion detector 16, or at least 10% of the internal diameter I of the drift chamber 14.

[0051] To generate a laminar flow of the sample gas through the ion mobility spectrometer, it is advantageous if the feed channel 4 and the discharge channel 5 are arranged essentially in axial alignment, or are at least placed on opposite sides of the ionization chamber 13.

[0052] From the manufacturing point of view, the feed channel 4 or the discharge channel 5 can be created, for example, through laterally milling the wall of the housing 2. The feed channel 4 or the discharge channel 5 can also be formed of a plurality of many individual adjacent channels or holes.

[0053] FIGS. 3 and 4 show further embodiments of the ion mobility spectrometer in respect of the supply of sample gas. FIG. 3 here corresponds to the embodiment already explained with reference to FIG. 2. In this embodiment, the ionization source 3 is mounted axially with respect to the longitudinal axis L of the ion mobility spectrometer 1 or of the drift chamber 14. The ionization source 3 can, for example, be implemented as a tritium source or as a UV source. The ionization source 3 can, moreover, also simultaneously constitute the counter electrode 11. If the ion detector 16 is sufficiently large, the principal ionization region in the ionization chamber 13 corresponds largely to the size of the ionization source 3.

[0054] FIG. 4 shows an embodiment in which the ionization source 3 is mounted away from the axis, for example orthogonally to the longitudinal axis L of the ion mobility spectrometer 1, and accordingly also radiates orthogonally to this into the ionization chamber 13. In this case, the ionization source 3 can, for example, be an x-ray source, a UV source or a laser. In this case, the ion mobility spectrometer 1 has an ionization channel 7 in the region of the ionization chamber 13, through which the radiation of the ionization source 3 is guided into the ionization chamber 13. The ionization channel 7 can be designed in a similar manner to the feed channel 4 or the discharge channel 5. The ionization channel 7 can, for example, be realized by a lateral milling in the housing 2. The primary ionization region here corresponds to the ion detector 16 indicated with a dashed line.

[0055] FIG. 5 shows an embodiment whose ionization source 3 is comparable to that of FIG. 3. In contrast to FIG. 3, the connecting channel 6 is made narrower, for example as a channel extending linearly without an enlargement or reduction in the cross-section. A laminar flow-through of the sample gas can be ensured in this way in a particularly efficient manner.

[0056] FIG. 6 shows an embodiment similar to that of FIG. 4, in which the ionization source 3 outputs its radiation into the ionization chamber 13 laterally through the ionization channel 7. The connecting channel 6 is comparable in design to that of FIG. 5, wherein, in this case, the ionization channel 7 opens into the connecting channel 6.

[0057] FIG. 7 shows an embodiment similar to that of FIG. 4, having however two parallel or nearly parallel drift chambers 14 according to DE 10 2018 107 910.9, with a common ionization chamber 13. The positions of the two ion detectors 16, and thereby the resulting primary ionization regions, are shown dashed. Since here the ionization source 3, the feed channel 4 and the discharge channel 5 are arranged orthogonally with respect to the drift direction, and the flow is to pass through the two primary ionization regions, an angled arrangement results between the ionization source 3 and the feed channel 4 or discharge channel 5 located at its side.