Separation of cis and trans Isomers of Polyproline by FAIMS Mass Spectrometry

High field asymmetric waveform ion mobility spectrometry (FAIMS) is well-established as a tool for separating peptide isomers (sequence inversions and post-translationally modified localization variants). Here, we demonstrate the FAIMS is able to differentiate cis and trans isomers of polyproline. Polyproline assumes an all-cis conformation—the PPI helix—in 1-propanol, and an all-trans conformation—the PPII helix—in aqueous solutions. Differentiation of these conformers may be achieved both through use of a cylindrical FAIMS device and a miniaturized ultrahigh field planar FAIMS device. [Figure: see text] ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s13361-016-1482-1) contains supplementary material, which is available to authorized users.