Numerical algorithm for the accurate evaluation of ion beams in transversal modulation ion mobility spectrometry: Understanding realistic geometries

• A numerical algorithm that estimated the resolving power of a transversal modulation ion mobility spectrometry, was developed.
• The algorithm was validated with experimental data.
• The algorithm revealed an aberration affect, which is negligible at the voltages commonly used, in the range of 10 kV.
• Using this algorithm, the geometrical parameters of the transversal modulation ion mobility spectrometry geometry were optimized.

In this study, we analyzed the different physical mechanisms that affect the shape of a thin ion beam in time-dependent electric fields for the particular configuration of a transversal modulation ion mobility spectrometry (TMIMS) device. In this configuration, the ion beam is focused in a narrow region, which is simultaneously broadened by diffusion; the quality and shape of this focus determines the resolving power of the spectrometer. We analyzed different numerical approaches and developed a compounded algorithm in which the diffusion effect is superimposed onto purely convective trajectories. With a relatively low computational cost, this method solves the challenges associated with the disparate scales of the problem. The new algorithm was validated against the experimental results, and it estimates the maximum resolving power of the spectrometer with errors below 10%. It also enabled an optimization of the geometry of the electrodes and the wave shape.

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