Figure 6.

Ultra-high-resolution 12 T FT-ICR MS positive ion microelectrospray ionization spectrum of a mixture of ¹⁵N₂-5foC and 5hmC showing a zoomed spectrum over a 60 mDa window. FT-ICR MS easily baseline resolves the biologically active 5hmC that differs in mass by only ~22 mDa from the isotope-labeled standard ¹⁵N₂-5foC. Mass accuracy was ~350 ppb for ¹⁵N₂-5foC and ~210 ppb for 5hmC. Spectra were acquired on a 12 T Bruker Solarix Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS).