Multipole storage assisted dissociation, a novel in-source dissociation technique for electrospray ionization generated ions

In this work we present a novel in-source dissociation scheme referred to as multipole storage assisted dissociation (MSAD) for electrospray ionization (ESI) generated ions in which dissociation is effected by employing extended ion accumulation intervals in a high pressure rf-only hexapole assembly prior to mass analysis. Following an extended ion accumulation interval in which ions are confined in the rf-only hexapole, ions are gated out of the hexapole, trapped, and mass analyzed in the trapped ion cell of a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. The accumulation region is comprised of an rf-only hexapole ion guide which separates two electrodes, a biased skimmer cone, and an auxiliary 'gate' electrode at the low pressure end of the hexapole. This technique should be applicable to other mass spectrometry platforms compatible with pulsed ionization sources including quadrupole ion traps, and time-of-flight mass analyzers. This concept is demonstrated with the dissociation of a small protein in which selective fragmentation is observed at labile amino acid linkages producing primarily y-type fragment ions.