Dissociation of Biomolecules by an Intense Low-Energy Electron Beam in a High Sensitivity Time-of-Flight Mass Spectrometer.

We report the progress on an electron-activated dissociation (EAD) device coupled to a quadrupole TOF mass spectrometer (QqTOF MS) developed in our group. This device features a new electron beam optics design allowing up to 100 times stronger electron currents in the reaction cell. The electron beam current reached the space-charge limit of 0.5 μA at near-zero electron kinetic energies. These advances enable fast and efficient dissociation of various analytes ranging from singly charged small molecules to multiply protonated proteins. Tunable electron energy provides access to different fragmentation regimes: ECD, hot ECD, and electron-impact excitation of ions from organics (EIEIO). The efficiency of the device was tested on a wide range of precursor charge states. The EAD device was installed in a QqTOF MS employing a novel trap-and-release strategy facilitating spatial mass focusing of ions at the center of the TOF accelerator. This technique increased the sensitivity 6-10 times and allows for the first time comprehensive structural lipidomics on an LC time scale. The system was evaluated for other compound classes such as intact proteins and glycopeptides. Application of hot ECD for the analysis of glycopeptides resulted in rich fragmentation with predominantly peptide backbone fragments; however, glycan fragments attributed to the ECD process were also observed. A standard small protein ubiquitin (8.6 kDa) was sequenced with 90% cleavage coverage at spectrum accumulation times of 100 ms and 98% at 800 ms. Comparable cleavage coverage for a medium-size protein (carbonic anhydrase: 29 kDa) could be achieved, albeit with longer accumulation times.