PNNL

Abstract

Continuing rapid development of the technology and applications of field asymmetric waveform ion mobility spectrometry (FAIMS) calls for better understanding of the limitations of this method and factors that govern them. While key performance metrics such as resolution and ion transmission efficiency had been calculated for specific cases using numerical simulations, the underlying physical trends remained obscure. Here we determine that the resolving power of planar FAIMS scales as the square root of separation time and sensitivity drops exponentially at the rate controlled by absolute ion mobility and several instrumental parameters. A strong dependence of ion transmission on mobility causes severe discrimination against species with higher mobility, presenting particular problems for analyses of complex mixtures. While the time evolution of resolution and sensitivity is virtually identical in existing FAIMS systems driven by gas flow and proposed devices driven by electric field, the distributions of separation times are not. The inverse correlation between mobility (and thus diffusion speed) and residence time for a particular species in field-driven FAIMS greatly reduces the mobility-based discrimination and provides much more uniform separations.