2.3. MALDI-TOF/TOF
MALDI–MS spectra were measured on a MALDI-TOF/TOF ultraFLEX III mass spectrometer (Bruker-Daltonics, Bremen, DE). Positive/negative spectra were calibrated externally using the monoisotopic [M+H]+ or [M−H]− ions of PepMixII calibrant (Bruker-Daltonics).