Ion Trajectory Simulations
SIMION-SDS simulations were used as the primary tool for exploring different electrode configurations and dimensions. For a detailed discussion of the SDS algorithm within the SIMION environment, see Sect. 1.3. Electrode geometries were constructed in the script-based geometry (.GEM) file format such that the density of the potential array points and electrode dimensions could be varied parametrically. Through the use of the GEM format it was possible to simplify the simulation environment to be cylindrically symmetric, thus solutions to the electric fields and resulting trajectory simulations were reduced in computational complexity. Simplification of the electrode geometry in such a manner does not allow for perfect representation of the true experimental setup, but serves to explore the feasibility of different electrode dimensions.
Unless otherwise stated, simulations used a potential array grid unit (GU) density of 0.04 mm/GU and a trajectory quality setting of zero. This means that time steps within the simulation are fixed such that integration steps occur over the distance of one GU. All simulations were performed neglecting the effects of space-charge. The reduced mobilities (K0) and masses of, tetrabutyl-, tetrahexyl-, tetraoctyl-, and tetradodecylammonium cations were specified within the simulation environment and the effective diameter of each was estimated from this data by the SDS algorithm. Each simulation was performed at atmospheric pressure (760 Torr) in air at 25 °C with no bulk gas flow.