Extending the isotopically resolved mass range of Orbitrap mass spectrometers.

The routine analysis of large biomolecules (greater than 30 kDa) has been a challenge for Orbitrap mass spectrometers due to the relatively high kinetic energy of ions entering and within the Orbitrap mass analyzer. This characteristic results in rapid signal decay for large biomolecules due to energetic collisions with background gas molecules. Here, we report a method to significantly enhance the analysis of large biomolecules in an Orbitrap mass spectrometer. The combination of reduced C-trap and higher energy collisional dissociation (HCD) cell bath gas pressures, using helium as the bath gas and trapping ions in the HCD cell prior to mass analysis, greatly increased sensitivity and reduced signal decay for large protein ions. As a result, isotopic resolution of monoclonal immunoglobulin G was achieved, and we have established a new high-mass record for which accurate mass measurement and isotopic resolution have been achieved.