PNNL

Abstract

Microchip-based field asymmetric waveform ion mobility spectrometry (FAIMS) analyzers featuring a grid of 35 µm - wide channels have allowed electric field intensity (E) over 60 kV/cm, or about twice that in previous devices with >0.5 mm gaps. Since separation speed scales as E4 to E6, these chips filter ions in just ~20 µs (or ~100 - 10,000 times faster than “macroscopic” designs), although with reduced resolution. Here we report integration of these chips into electrospray ionization (ESI) mass spectrometry, with ESI coupled to FAIMS via a curtain plate/orifice interface with edgewise ion injection into the gap. Adjusting gas flows in the system permits control of ion residence time in FAIMS that affects resolving power independently of ion desolvation after the ESI source, and the results agree with a priori simulations and scaling rules. Exemplary applications include analyses of amino acids, peptides, and whole proteins. Because of limited resolving power, present FAIMS is mostly useful for distinguishing compound classes rather than species within them. In particular, peptides separate from other ions, and large proteins fully separate from smaller proteins and peptides (likely because the field in FAIMS reversibly aligns the macroions with sufficiently strong electric dipoles).