PNNL

Abstract

Field Asymmetric waverform Ion Mobility Spectrometry (FAIMS) holds significant promise for post-ionization separations in conjunction with mass-spectrometric analyses. Since commercial systems became available, applications of FAIMS/MS have expanded in scope. However, a relatively poor understanding of fundamentals of FAIMS analyzers has made their design and operation an essentially empirical exercise. Recently we developed a first-principles simulation of FAIMS that accounts for both ion diffusion (including high-field and anisotropic components) and Coulomb repulsion. This model has been validated by extensive comparisons with FAIMS/MS data. Here we further corroborate it by FAIMS-only measurements, and apply it to explore how key instrumental parameters (analytical gap width and length, waveform frequency and profile, the buffer gas identity, and gas flow speed) affect FAIMS response. We find that the trade-off between resolution and sensitivity can be managed by varying gap width, RF frequency, and (in certain cases) buffer gas, with equivalent outcome. The maximum resolving power attainable is ~ 30 - 40. Throughput may be increased by either accelerating the gas flow (preferable) or shortening the device, but at some point the performance starts deteriorating. Resolution and/or sensitivity would be improved by switching from sinusoidalbased to retangular waveforms. For both, the ratio of two between voltages at "high" and "low" parts of the cycle produces best performance.