Characterizing the Top-down Sequencing of Protein Ions Prior to Mobility Separation in a timsTOF

Mass spectrometry (MS)-based proteomics workflows of intact protein ions have increasingly been utilized to study bio-logical systems. These workflows, however, frequently result in convoluted and difficult to analyze mass spectra. Ion mobility spectrometry (IMS) is a promising method to overcome these limitations by separating ions by their mass- and size-to-charge ratios. In this work, we further characterize a newly developed method to collisionally dissociate intact protein ions in a trapped ion mobility spectrometry (TIMS) device. Dissociation occurs prior to ion mobility separation and thus, all product ions are distributed throughout the mobility dimension, enabling facile assignment of near isobaric product ions. We demonstrate that collisional activation within a TIMS device is capable of dissociating protein ions up to 66 kDa. We also demonstrate that the filling of the TIMS device significantly influence the efficiency of fragmentation. Lastly, we compare CIDtims to the other modes of collisional activation available on the Bruker timsTOF and demon-strate that the mobility resolution in CIDtims enables the annotation of overlapping fragment ions and improves sequence coverage.