Using a matrix-assisted laser desorption ionization time-of-flight mass spectrometer for combined in-source decay/post-source decay experiments

Mass spectrometric experiments with fragment ions have not yet been possibl e with a matrix-assisted laser desorption/ionization time-of-flight (MALDI- TOF) mass spectrometer because intense signals of fragment ions were rarely observed during continuous extraction and the mass resolution of in-source formed fragment ions has been low. This paper describes a combination of M ALDI in-source decay and post-source decay experiments on a MALDI-TOF mass spectrometer equipped with delayed extraction. Fragment ions initially form ed in the ion source were selected by the precursor ion gate and investigat ed by post-source decay. The in-source formed fragment ions were sufficient ly excited to undergo further metastable decay, The new method was applied to linear peptides, the cyclic peptide gramicidin S and a pentasaccharide, leading to unambiguous structural information. Copyright (C) 1999 John Wile y & Sons, Ltd.