Abstract
In-source decay (ISD) combined with matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometer (TOF MS) has been described by comparing with conventional mass spectrometric degradation (MSD) methods such as collision-induced dissociation (CID) and post-source decay (PSD). The ISD characteristic is the formation of c- and (z+2)-ions originated from the N-Cα bond cleavage on the peptide backbone, while the CID and PSD processes are the CO-NH bond cleavage which brings about b- and y-ion. Furthermore, the ISD processes occurring with 337 nm laser photon irradiation for peptide or protein proceed resulting in the formation of hyper-valent radical species via intermolecular hydrogen transfer between matrix and analyte molecules following the non-ergodic N-Cα bond cleavage. The non-ergodic N-Cα bond cleavage occurs in the MALDI ion source within nanosecond order, as an α-cleavage initiated with radical site at the carbonyl carbon. The MALDI-ISD method has been applied to three peptides and five proteins.
