FOCUS: MOBILE PROTON MODEL Separation and Identification of Structural Isomers by Quadrupole Collision-Induced Dissociation-Hydrogen/Deuterium Exchange-Infrared Multiphoton Dissociation (QCID-HDX-IRMPD)

A new approach that uses a hybrid Q-FTICR instrument and combines quadrupole collisioninduced dissociation, hydrogen-deuterium exchange, and infrared multiphoton dissociation (QCID-HDX-IRMPD) has been shown to effectively separate and differentiate isomeric fragment ion structures present at the same m/z. This method was used to study protonated YAGFL-OH (free acid), YAGFL-NH2 (amide), cyclic YAGFL, and YAGFL-OCH3 (methyl ester). QCID-HDX of m/z 552.28 (C29H38N5O6) from YAGFL-OH reveals at least two distributions of ions corresponding to the b5 ion and a non-C-terminal water loss ion structure. Subsequent IRMPD fragmentation of each population shows distinct fragmentation patterns, reflecting the different structures from which they arise. This contrasts with data for YAGFL-NH2 and YAGFL-OCH3, which do not show two distinct H/D exchange populations for the C29H38N5O6 structure formed by NH3 and HOCH3 loss, respectively. Relative extents of exchange for C29H38N5O6 ions from six sequence isomers (YAGFL, AGFLY, GFLYA, FLYAG, LYAGF, and LFGAY) show a sequence dependence of relative isomer abundance. Supporting action IRMPD spectroscopy data are also presented herein and also show that multiple structures are present for the C29H38N5O6 species from YAGFL-OH. (J Am Soc Mass Spectrom 2010, 21, 1329–1338) © 2010 Published by Elsevier Inc. on behalf of American Society forMass Spectrometry