Finite-element analysis of a miniaturized ion mobility spectrometer for security applications

Abstract

A miniaturized Planar Field Asymmetric Ion Mobility Spectrometer (P-FAIMS) has been simulated in N2 at ambient pressure using COMSOL Multiphysics software. Micro-IMS is based on ion gas-phase separation due to the dependence of ion mobility with electric field. Ions are selected by a DC voltage characteristic of each kind of ion. The average kinetic behaviour of ions in high electric fields conditions is well known but not the chemical reactions and physical collisions related with. The aim of this work is the modelling of the average kinetic behaviour of different kind of ions in a P-FAIMS taking into account the main factors involved in their movement. Three different compounds, with high impact on security applications, have been studied: an explosive 2,4,6-trinitrotouluene (TNT−H)−, a volatile organic compound Ac2H+ and a chemical warfare agent simulant DMMPH+ that emulates gas sarin. Displacement simulations along the P-FAIMS of theirs vapour phase ions have been done at different values of drift electric field amplitude to gas number density (E/N) ratio. Ions were selected between the ones present in the literature that covers the previous applications and the ones with more reliable experimental data of the main parameters involved in the definition of ions mobility needed for their analysis. Results show that simulations of ions behaviour in a P-FAIMS are possible with COMSOL Multiphysics software and that the time and intensity at which ions are detected are in good agreement with an experimental data in the literature.