IONIZATION MECHANISMS IN MATRIX-ASSISTED LASER-DESORPTION IONIZATION MASS-SPECTROMETRY - CONTRIBUTION OF PREFORMED IONS

The mechanisms of ion formation in matrix-assisted laser desorption/io nization mass spectrometry are still largely unknown, Ions may exist a s pre-formed species in the solid state, or may form by ion-molecule r eactions initiated by the laser shot, or, most probably, they may orig inate from a combination of both processes, The contribution of pre-fo rmed ions was approached from the standpoint of coordination chemistry and studied in different transition metal ion/matrix systems as well as in the copper/polystyrene system, The solution, the solid and the g as phases were investigated by means of infrared, visible and proton n uclear magnetic resonance spectroscopy, as well as by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. It was found th at the contribution of pre-formed ions can be predicted on the basis o f condensed phase thermodynamics, MALDI mass spectra qualitatively ref lect the amount of pre-formed complexes in the solid target. (C) 1997 by John Wiley & Sons, Ltd.