Ion mobility spectrometry is a method used to identify the composition of a sample of ions using ion mobility. Ion mobility spectrometers can be employed at security checkpoints, such as airports, to assist in the detection of explosives and narcotics. When used at airports, for example, residue from luggage can be transferred to a swab, which can be manipulated so that molecules and/or atoms associated with the residue pass into an ionization region within the ion mobility spectrometer. In the ionization region, the molecules and atoms associated with the residue can be ionized. Both positive and negative ions can form in the ionization region. An electric field at grids spaced between the ionization region and a drift region can be pulsed to allow ions to pass from the ionization region into the drift region. The ions in the drift region can be further subject to a force as a result of an electric field maintained in the drift region. Once in the drift region, the ions can separate based upon the ions' respective ion mobility. In this way, a time-of-flight measurement of the ions in the drift region (which can be measured as a change in current magnitude on a collector plate at one end of the drift region), can provide an identifying peak in a measured current magnitude, and which can be associated with a particular ion. The plot of current magnitude at the collector as a function of time is referred to as a plasmagram.