Letter: Matrix-Assisted Laser Desorption/Ionization and Electrospray Ionization Mass Spectrometry: Sodium-Cationized Oligosaccharides Do Not Exhibit “Internal-Residue Loss” Rearrangement

A series of methylgalactotrioses, in which one or two residues were specifically deoxygenated and labeled with a fluorine atom in the C-3 position, were used as models for the study of “internal residue loss” (IRL) under the conditions of matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) and electrospray ionization (ESI) techniques. Under the conditions of measurement of MALDI-TOF post-source decay and ESI in-source decay of methyl oligosaccharides, the IRL rearrangement of [M + Na]⁺ ions did not take place.