This application claims the priority of German patent document 196 50 612.3, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an ion mobility spectrometer with an ion gate, a drift chamber, and an ion collector.
An ion mobility spectrometer of this generic type is described for example in European patent document EP 0 046 699 and in U.S. Pat. No. 4,390,784. It is essentially based on the fact that ions migrate to the ion collector in the drift chamber under the influence of an electrostatic field. The drift time is different for different ions and is determined by their mobility. The known ion mobility spectrometer has a drift chamber cross section of several square centimeters and drift distances up to 40 cm. The dimensions and high price of such devices limit the type and number of applications that lend themselves to this measurement method.
Attempts therefore have been made to miniaturize ion mobility spectrometers (International Journal of Environmental Analytical Chemistry, 1993, Volume 52, pages 189-193). Implementation of the concept described therein however has proven to be difficult or impossible, since the requirements for the individual components can be met only with difficulty if at all. No mention is made in the above article of the technical implementation of a miniaturized ion gate.
Hence, the object of the present invention is to provide an ion mobility spectrometer that can be miniaturized, and which can be manufactured using conventional methods, especially those known from semiconductor manufacturing.
Another object of the invention is to provide an ion mobility spectrometer which is small and less expensive to manufacture than known prior art devices.
These and other objects and advantages are achieved by an ion mobility spectrometer (IMS) according to the invention, in which the essential parts, namely the ion gate, the drift chamber, and the ion collector, consist of pieces that are essentially slice or wafer shaped, which are either anisotropically etchable or can be machined using micromechanical methods, and are held together by clamps, adhesives, or other assembly methods that are known of themselves. In the simplest form, the drift chamber consists of two sliced pieces with a through groove being etched or milled in one of them. The groove is covered by the other smooth piece so that a drift channel is produced. The drift channel is closed at one end by a grid-shaped ion gate, which is similarly made from a sliced piece by etching or milling, while the opposite end of the drift channel is closed by the ion collector, which is likewise made from a sliced piece that is electrically conducting on the inside.
In this manner, an IMS can be produced with a drift chamber cross section of less than 1 cm and a length of approximately 4 cm; in other words dimensions that correspond to about 1/10 of the previously conventional device measurements. The ionization chamber, which directly abuts the ion gate, can also be made in the same fashion.
Because of the small dimensions of the drift chamber, the measurement pulses are nearly delta-shaped with proper control of the ion gate, so that a detection limit for specific ions in the ppm range can be set. The power draw of the device can therefore be kept below 2 watts.
Because of its miniaturization, its low energy demand, and its low cost, the IMS can be used for drug or dangerous substance detection in the field, and can also be used for example as a monitoring device on high-voltage switches, which are filled with a protective gas (sulfur hexafluoride), whose concentration must be constantly monitored. Thus, frequent changing of the protective gas can therefore be eliminated.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.