Abstract: Ion Mobility Spectrometry (IMS) equipment comprises an enclosed compartment (10) contained within which there is an IMS cell (12) and a body of absorbent material (14). Samples for detection by the cell (12) are introduced into the compartment (10) by means of a pinhole (30), the samples being drawn in by a negative pressure pulse within the compartment produced by means of a loudspeaker (40). A sample, once it has been drawn in and detected by the cell (12), will diffuse within the compartment (10) and any water vapour or other interfering species thus introduced will be absorbed by the absorbent material (14) so maintaining a clean, dry atmosphere within the device.

Abstract: A detector for trace quantities of chemical species in the atmosphere includes a pump for drawing an atmospheric sample through transfer means which transfer species molecules present in the sample to a dry carrier gas circulating in a closed gas flow circuit including the transfer means, an ionmobility type detector, filters and a circulating pump; the filters remove water molecules and species molecules from the carrier gas. The carrier gas may be air. The arrangement inhibits water vapor reaching the detector and reducing its sensitivity to the chemical species.

Abstract: An apparatus is provided for detecting trace quantities of chemical species in the form of a vapor by subjecting ions produced in a sample of the mixed gas under flow to an ion repulsive electric field which is directed in the opposite direction to the flow of the gases, and comprises a fan for drawing the sample through a hollow body, having an inlet, a first region containing means for ionizing at least a proportion of the molecules of the sample by a corona discharge, a second region in which the sample is subjected to an oppositely directed ion repulsive electric field and a third region having an electrode for collecting ions of selected polarity. Ions of a selected polarity whose ionic mobilities exceed a value dependent on the strength of the ion repulsive electric field and the velocity of the gas flow are prevented from entering the third region. A resistor may be provided to limit the current of the corona electric discharge to a value not greater than 100 nanoamps.

Abstract: An apparatus for detecting the presence of volatile, organic substances in gaseous mixtures comprises a filament on which the substances are absorbed when the filament is cold and released when hot, an electron capture device to detect the emitted substances, a primary and a secondary flow of inert gas, and a valve system in which system an inlet valve which admits the gaseous mixture automatically closes when the gas pressure of the gases within the apparatus exceeds the ambient pressure, the presence of the volatile organic substances being indicated by an output signal from the electron capture device. The apparatus alternatively may be used for controlling the flow of gases containing organic volatile substances.The filament may be sensitive to specific vapors.