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 H2. 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 N2 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.