An ion mobility spectrometer (IMS) is developed for use as an analytical tool and, in particular, for the detection of species used as explosives. From the initial design based on the literature, we have, through several optimization studies, reached a configuration that provides the desired sensitivity with adequate resolution. Results obtained with the optimized geometry are presented in this article. The sensitivity of the instrument is about 10 ng for 2,4,6-trinitrotoluene (TNT) and Royal Demolition Explosive or cyclotrimethylene trinitramine (RDX) and about 50 ng for pentaerythritol tetranitrate (PETN). These explosives are detected as clearly resolved features.