Field desorption collision activation linked scanning mass spectrometry of underivatized oligopeptides

Field desorption production of protonated molecular ions from nanomole amounts of chemically underivatized penta-, tetra- and dipeptides, coupled with collision induced decomposition of [M + H]+ ions, yielded partial amino acid sequence information. Linked scanning of two of the three fields detected ions produced in the first field free region of a double focusing mass spectrometer.