Separation of β-Amyloid Tryptic Peptide Species with Isomerized and Racemized l-Aspartic Residues with Ion Mobility in Structures for Lossless Ion Manipulations.

Accumulation of β-amyloid (Aβ) is one of the hallmarks of Alzheimer's disease. The deposition of β-amyloid plaques is likely to start years in advance of manifestation of clinical symptoms, although the exact timing is unknown. Over the years, Aβ peptides undergo both post-translational modification and stereoisomerization. Analysis of the resulting stereoisomers is particularly challenging because of their identical elemental composition and similar physicochemical properties. Herein, we have utilized our recently developed structures for lossless ion manipulations ion mobility-mass spectrometry platform (SLIM IM-MS), in conjunction with serpentine ultralong path with extended routing (SUPER), to baseline resolve four distinct sets of Aβ17-28 tryptic peptide epimers on a rapid (∼1 s) time scale. We discovered that sodium adduct ions, [M + H + Na]2+, allowed baseline SLIM SUPER IM resolution for all Aβ epimer sets assessed, while such baseline separations were unachievable for their [M + 2H]2+ doubly protonated ions.