Fourier Transform-Ion Mobility-Orbitrap Mass Spectrometer: A Next-Generation Instrument for Native Mass Spectrometry

A new instrument configuration for native ion mobility-mass spectrometry (IM-MS) is described. Macromolecule ions are generated by using a static ESI source coupled to an RF ion funnel, and these ions are then mobility and mass analyzed using a periodic focusing drift tube IM analyzer and an Orbitrap mass spectrometer. The instrument design retains the capabilities for first-principles determination of rotationally averaged ion neutral collision cross sections and high-resolution measurements in both mobility and mass analysis modes for intact protein complexes. Operation in the IM mode utilizes FT-IMS modes (originally described by Knorr (Knorr, F. J. et al. Anal. Chem. 1985, 57(2), 402-406)), which provides a means to overcome the inherent duty cycle mismatch for drift tube (DT)-IM and Orbitrap mass analysis. The performance of the native ESI-FT-DT-IM-Orbitrap MS instrument was evaluated using the protein complexes Gln K (MW 44 kDa) and streptavidin (MW 53 kDa) bound to small molecules (ADP and biotin, respectively) and transthyretin (MW 56 kDa) bound to thyroxine and zinc.