An ion mobility spectrometer analytical instrument, including an ion mobility spectrometer, a swab interface, and a desorber assembly. The desorber assembly includes a heat transfer device configured to heat a desorber, as well as a supply configured to direct gas through the desorber. The instrument further includes a drift tube, high voltage device arrayed, at least in part, proximate to the drift tube, wherein the high voltage device is configured to change a polarity of a voltage applied to the drift tube and have an absolute voltage of about 500 to 1500 volts. The instrument further includes a reactant supply unit adapted to supply reactant during a sample substance analysis, and a control unit.