SOFTWARE SIMULATION OF ION MOTION IN DC AND AC ELECTRIC FIELDS INCLUDING FLUID-FLOW EFFECTS (SIONEX microDMx SOFTWARE) Erkinjon G. Nazarov , Raanan A. Miller, Stephen L. Coy, Evgeny Krylov, Sergey I. Kryuchkov Sionex Corporation, 8-A Preston Ct., Bedford MA 01730 USA Background Development of new mobility-based analyzers can be greatly speeded up if ion behavior in the analytical region can be reliably simulated. For that reason, we began the development of computational software able to simulate ion movement in different designs of differential mobility spectrometers (DMS) including the well-established planar (DMS) and cylindrical (FAIMS) geometries. We want to use the tool to simulate ion trajectories for each ion species (specific mobility coefficients and alpha parameters) for arbitrary DC and AC electric fields and dynamic gas flows. There are a few commercial software packages that are able, with some effort, to simulate ion motion in atmospheric pressure conditions. These include SIMION 7.0 and a special version of Lorentz from Integrated Engineering Software. 1, 2 They are able to model traditional time of flight type ion mobility spectrometers (IMS). In addition, some publications have been devoted to the modeling of ion movement in differential mobility spectrometry (FAIMS). 3,4 In the current work we have gone beyond the capabilities of commercially-available software to build a robust, flexible computational tool for simulation of ion motion in any kind of analytical devices which operating under near-ambient pressure conditions. Devices that can be modeled include IMS, DMS-FAIMS and other differential mobility analyzers (DMA) where ion velocity is used for characterization and identification. Purpose: A simulation tool for differential mobility spectrometry The simulation software is primarily intended to model DMS, which is based on distinctly different operating principles from IMS. Figure 1a shows a schematic of the DMS which consists of analytical gap between two parallel plates. Swarms of ions are carried by transport gas through the analytical gap under laminar flow conditions. Both positive and negative ions are carried together through the analytical gap by the transport gas and can be separately detected at the exit of the analytical gap. In DMS (Figure 1a), ions are separated at ambient pressure according to the field dependence of their drift velocities (given by the mobility equation, () ( ( ))* () t KEt Et ϑ = r r ). DMS separation is based on the non-linear dependence of the mobility coefficient K(E) shown in eq (1), 2 4 2 4 () (0)[1 ( / ) ( / ) .... ] (0)[1 ( / )] KE K EN EN K EN α α α = + + + = + (1) Where: K(0) is the mobility coefficient for low electric field (E) conditions; and the i α parameters show the dependence of K on the electric field, and N is density of gas molecules.