Drift tube for an ion mobility spectrometer with integrated gas channel
A drift tube for an ion mobility spectrometer is assembled from stacked tube segments and has electrodes that generate an electric drift field and are electrically contactable from the outside of the drift tube. Most of the tube segments have at least two separate apertures so that, when the segments are stacked, these apertures form a drift region and at least one integrated gas channel both of which run parallel to the axis of the drift tube. At least one tube segment is inserted into the stack in which the two apertures are connected to form a gas channel transverse to the axis of the drift tube so that the drift region is connected to the gas channel at that tube segment.
1. A drift tube for use in an ion mobility spectrometer, having an axis and comprising:
a plurality of tube segments, each of the tube segments having a first aperture and a second aperture, unconnected to the first aperture, both apertures passing through that tube segment;
means for connecting the tube segments in a stack with gas-tight connections between the tube segments so that the first apertures line up to form a drift region having a constant cross-section and extending along the axis of the drift tube and the second apertures line up to form a gas channel extending parallel to the axis of the drift tube; and
wherein at least one tube segment having a first aperture and a second aperture connected to the first aperture by a gas channel that extends transverse to the axis of the drift tube, is inserted into the stack so that the first aperture lines up with the drift region and the second aperture lines up with the gas channel and the drift region is connected to the gas channel at the location of that tube segment.
2. A drift tube according to claim 1 , wherein each of the tube segments has three apertures passing therethrough and arranged so that, when the tube segments are stacked, the three apertures form a drift region and two gas channels extending along the axis of the drift tube and wherein at least one connecting tube segment is inserted into the stack which connects the two gas channels extending along the axis of the drift tube with each other and with the outer region of the ion mobility spectrometer.
3. A drift tube according to claim 1 , wherein each of the tube segments is fabricated from an electrically insulating material.
4. A drift tube according to claim 3 , further comprising an electrically conductive layer located between each pair of tube segments in the stack.
5. A drift tube according to claim 4 wherein each electrically conductive layer extends from the first aperture to the exterior of the drift tube where that layer is electrically connected to a voltage supply.
6. A drift tube according to claim 3 , wherein tube segments are fabricated from electrically insulating materials and electrically conducting materials.
7. A drift tube according to claim 6 wherein each tube segment fabricated from electrically conductive materials electrically connects the first aperture to the exterior of the drift tube where that tube segment is electrically connected to a voltage supply.
8. A drift tube according to claim 6 , wherein the electrically conductive tube segments are fabricated from one of the group consisting of metal, a conductive plastic, a conductive ceramic, a conductively coated plastic and a conductively coated ceramic.
9. A drift tube according to claim 3 , wherein the insulating tube segments are fabricated from one of the group consisting of ceramic and plastic.
10. A drift tube according to claim 1 , wherein at least one of the tube segments has a contact surface comprising a planar extension which, when the at least one tube segment is assembled in the stack, extends perpendicular to the axis of the drift tube.
11. A drift tube according to claim 1 , wherein the stack is mechanically self-supporting.
12. A drift tube according to claim 11 , wherein the stack is part of the mechanical support structure of the ion mobility spectrometer.
13. A drift tube according to claim 1 , further comprising a filter material and/or doping material located in the gas channel.
14. A drift tube according to claim 1 , wherein at least one of the tube segments comprises formed elements or sealing surfaces for contacting pneumatic components or sensors.