Tandem Mass Spectrometry of Peptide Ions by Microwave Excited Hydrogen and Water Plasmas

A thermal cracking cell that served as the atomic hydrogen source for hydrogen attachment/abstraction dissociation (HAD) analysis has an intrinsic problem to produce a beam of atoms reactive against heated tungsten capillary. A plasma excited by 2.45 GHz microwave discharge can deliver reactive species to a quadrupole ion trap confining analyte ions without excessive heating of the radical source components. The radical (H^•) production performance of the developed source was evaluated by optical emission spectroscopy and H^• attachment reaction to fullerene ions. The source exhibited the H^• attachment rate as high as a thermal cracking source forming H^• in the high temperature tungsten capillary to induce fragmentation processes preserving post-translational modifications. Water vapor was introduced to the source to confirm the stability to generate oxygen containing radicals, which were found present in the water vapor plasma together with atomic hydrogen. Injection of radicals from a water vapor plasma successfully dissociated peptide ions to c-/z- and a-/x-type ions as the case of HAD induced by a thermal cracking cell.