Fragmentation of vitamin B-12 in aerosol matrix-assisted laser desorption ionization

Aerosol matrix-assisted laser desorption ionization (MALDI) with a reflectron time-of-flight mass spectrometer was used to study fragmentation of vitamin B-12. Six MALDI matrices were used: 2,5-di-hydroxy benzoic acid (gentisic acid), 4-nitroaniline, 3,5-dimethoxy-4-hydroxy cinnamic acid (sinapic acid), 3,4-di-hydroxy cinnamic acid (caffeic acid), trans-4-hydroxy-3-methoxy cinnamic acid (ferulic acid), and alpha-cyano-4-hydroxy cinnamic acid (4-HCCA). Mass spectra were obtained with a 355-nm pulsed Nd:YAG laser at irradiances between 0.1 and 5 GW/cm(2) (between 3- and 150-mJ pulse energy). Loss of CN was a major product of prompt ion source fragmentation and the ratio of fragmented to intact analyte was found to be strongly dependent on matrix and weakly dependent on laser irradiance. Additionally, free cobalt ions and cobalt ions bound to small methanol clusters were observed in the mass spectra. The cobalt removal from the corrin ring of vitamin B-12 results from direct photon absorption by vitamin B-12, but is enhanced by the presence of matrix. (C) 1997 American Society for Mass Spectrometry