STRUCTURAL CHARACTERIZATION OF PHOSPHOLIPIDS BY MATRIX-ASSISTED LASER-DESORPTION IONIZATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

Matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry provides for structural anal ysis of the principal biological phospholipids: glycerophosphatidylcho line, -ethanolamine, -serine, and -inositol. Both positive and negativ e molecular or quasimolecular ions are generated in high abundance. Is olated molecular ions may be collisionally activated in the source sid e of a dual trap mass analyzer, yielding fragments sewing to identify the polar head group (positive ion mode) and fatty acid side chains (n egative ion mode), Azimuthal quadrupolar excitation following collisio nally activated dissociation refocuses product ions close to the solen oid axis; subsequent transfer of product ions to the analyzer ion trap allows for high-resolution mass analysis. Cyro-cooling of the sample probe with liquid nitrogen greatly reduces matrix adduction encountere d in the negative ion mode.