Improved Performance of Positive-Ion Mode Free Radical-Initiated Peptide Sequencing with

Free radical-initiated peptide sequencing (FRIPS) is a tandem mass spectrometry technique that generates sequence informative ions via collisionally initiated radical chemistry. Collision activation homolytically cleaves an installed radical precursor and initiates radical formation, extensive hydrogen atom transfer, and peptide backbone dissociation. While the FRIPS technique shows great promise, when applied to multiply charged derivatized peptide ions, a series of high-abundance mass losses are observed which siphon ion abundance from radically generated sequence ions. This loss of ion abundance reduces the sequence coverage generated by FRIPS fragmentation. In this work, we hypothesized that these mass losses were assisted by the