Atmospheric pressure MALDI/ion trap mass spectrometry

A new sample ionization technique, atmospheric pressure matrix-assisted las er desorption/ionization (AP MALDI), was coupled with a commercial ion trap mass spectrometer. This configuration enables the application-specific sel ection of external atmospheric ionization sources: the electrospray/APCI (c ommercially available) and AP MALDI (built in-house), which can be readily interchanged within minutes. The detection limit of the novel AP MALDI/ion trap is 10-50 fmol of analyte deposited on the target surface for a four-co mponent mixture of peptides with 800-1700 molecular weight. The possibility of peptide structural analysis by MS/MS and MS3 experiments for AP MALDI-g enerated ions was demonstrated for the first time.