SUPPRESSION OF METASTABLE INTERFERENCE IN MATRIX-ASSISTED LASER-DESORPTION IONIZATION (MALDI) SPECTRA IN A REFLECTING TIME-OF-FLIGHT MASS-SPECTROMETER

Metastable interference in matrix-assisted laser desorption/ionization (MALDI) spectra is reduced by modulating the accelerating potential (by < approximately 100 V) on alternate laser shots. Both parent and daughter ions are reflected on every second shot but only daughter ions are reflected on the next shot. The parent-ion spectrum is then obtained by subtraction. In order to ensure the necessary well defined energy distributions, signals with similar intensity (preferably small) are selected by transferring each transient to a computer for examination. This procedure decreases the complexity in reflected spectra (especially spectra of mixtures) in the lower mass range and improves the mass resolution in the intermediate mass range around 10 000 u. Continuous background in reflected spectra is also suppressed by the technique.