Fragmentation of vitamin B12 during 337 nm matrix-assisted laser desorption ionization

Matrix-assisted laser desorption ionization of vitamin B12 at 337 nm yields low abundances of the protonated molecule in time-of-flight mass spectra when the matrix α-cyano-4-hydroxycinnamic acid is used. A variety of fragment ions are observed in the time-of-flight mass spectra which may be assigned on the basis of previous studies of vitamin B12 fragmentation. When the matrix 4-hydroxy-3-iodo-5-nitrobenzoic acid is used, an abundant signal from the protonated molecule ion of vitamin B12 is produced. Fragment ions are still observed in the time-of-flight mass spectra but at much lower abundances. Studies of the influence of matrix-to-analyte ratio and desorbing laser intensity argue against direct photodissociation as the mechanism of fragment ion formation. Matrix choice appears to most strongly influence the internal energies of the laser-desorbed ions thereby controlling the fragmentation processes.