Comparison if sustained off-resonance irradiation collisionally activated dissociation and multipole storage-assisted dissociation for top-down protein analysis

Tandem mass spectrometric data acquired for small (8-18 kDa) intact proteins by sustained off-resonance irradiation collisionally activated dissociation (SORI-CAD) and multipole storage-assisted dissociation (MSAD) were compared, and the results indicate that the two activation methods do not always provide the same fragmentation patterns. In MSAD experiments, the charge state distribution made available by the ionization conditions may dictate the range of fragment ions that can be generated. In addition, conditions of high space charge within the hexapole impair transmission and/or trapping of high m/z species, which can result in loss of important precursor and product ions. Finally, the non-resonant nature of activation in MSAD can provide access to secondary dissociation processes that are not available by SORI. Because of these considerations, MSAD is less reliable than SORI for generating sequence tag data. However, it appears that MSAD samples 'preferred' cleavage processes (i.e. those occurring at D and P residues) just as well as SORI, which implies that MSAD data may be somewhat more compatible with search algorithms that utilize unprocessed fragment ion masses.