Ultraviolet-laser desorption/ionization mass spectrometry of femtomolar amounts of large proteins

Proteins with molecular weights between 14 000 and 175 000 daltons were investigated by matrix-assisted laser desorption/ionization mass spectrometry. High abundance molecular ions were obtained with absolute sample amounts ranging from 5 pmol down to 50 fmol, allowing molecular weight determination with an accuracy between 0.1 and 0.2%. The amount of sample needed for an analysis is determined by the preparation rather than by the mass analysis step; the majority of the sample can be regained after analysis.