ABSTRACT
The theory underlying ion mobility spectrometry (IMS) describes the motion of slow ions in gases. As the ion moves through a neutral gas (supporting atmosphere) under the influence of an external electric field, different forces act on it. On the one hand, there are forces due to the resistance encountered by the ion from the gas molecules. These are electrostatic forces as well as forces arising from the geometry (size and structure) of the ion and molecules. On the other hand, a diffusive force arising from a concentration gradient of the ions and the influence of the electric field act to enhance ion motion. Therefore, when trying to analyze the phenomenon of ion mobility, must be taken account for the diffusion and nonelectrostatic interaction between the ion and gas molecules, the electrostatic interactions between the ion and polarizable gas molecules, and the effect of the electric field on ion motion.
