Differential Ion Mobility Separations/Mass Spectrometry with High Resolution in Both Dimensions

Strong orthogonality to mass spectrometry makes differential ion mobility spectrometry (FAIMS) a powerful tool for isomer separations. However, high FAIMS resolution has been achieved overall only with buffers rich in He or H-2. That obstructed coupling to Fourier transform mass spectrometers operating under ultrahigh vacuum, but exceptional m/z resolution and accuracy of FTMS are indispensable for frontline biological and environmental applications. By raising the waveform amplitude to 6 kV, we enabled high FAIMS resolution using solely N-2 and thus straightforward integration with any MS platform: here Orbitrap XL with the electron transfer dissociation (ETD) option. The initial evaluation for complete histone tails (50 residues) with diverse post-translational modifications on alternative sites demonstrates a broad capability to separate and confidently identify the PTM localization variants in the middle-down range.