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.