ACTIVATED-ION ELECTRON TRANSFER DISSOCIATION (AI-ETD) PERFORMED IN A DEDICATED ETD REACTION CELL ON A HYBRID MASS SPECTROMETER LEADS TO UNPRECEDENTED PROTEOMIC SENSITIVITY

摘要

Electron capture dissociation and its descendent, electron transfer dissociation are invaluable tools for peptide and protein interrogation. The utility of ETD is restricted by at least two limitations: 1) An increased proclivity for nondissociative electron transfer (ETnoD) with increasing precursor m/z, and 2) ETD is generally conducted in devices not designed specifically for the purpose of conducting ETD. There have been several techniques described to mitigate the problematic effects of ETnoD, including socalled activated-ion ETD (AI-ETD). In this process, precursor peptide cations are subjected to IR irradiation concomitant to ion-ion ETD reactions. The IR photons impart internal energy to the peptides, resulting in more efficient ETD product yield presumably due to a more unfolded, ETD-friendly gas-phase secondary structure. The kinetics of ETD ion-ion reactions performed in a quadrupole linear trap (QLT) directly relate to the densities of the participating ions; more dense populations react at a higher rate. The densities can be increased by increasing the RF amplitude, increasing background gas pressure, or modifying the physical dimensions of the device. Making these adjustments, however, can adversely influence other important functions of the trap (e.g. trapping, isolation, and m/z analysis). Here we present an HCD cell modified to serve as a dedicated ETD reaction cell, designed to maximize ETD reaction rates; further, we perform ETD in this reaction cell in the presence of IR activation (AIETD), enhancing product ion yield.