Differential Ion Mobility Separations of Peptides with Resolving Power Exceeding 50

Differential ion mobility spectrometry (IMS) or field asymmetric waveform IMS (FAIMS) separates gas-phase ions by mobility differences with respect to the electric field intensity. A major emerging FAIMS application is the fractionation of proteolytic digests. Using a planar FAIMS unit with helium/nitrogen mixtures, we have increased FAIMS resolving powers for peptide analyses from the prior maximum of similar to 20-30 to similar to 50-70. The resolution improved nearly 3-fold, allowing, in particular, separation of previously unresolved conformers.