Purification of contaminated peptides and proteins on synthetic membrane surfaces for matrix-assisted laser desorption/ionization mass spectrometry.

Effective MALDI-TOF MS of salt-, detergent-, and glycerol-contaminated peptide and protein samples is accomplished by loading samples onto synthetic membranes, washing away contaminants, adding matrix, and desorbing samples directly from the membrane surface. The method easily removes contaminants which prevent effective MALDI of peptides and proteins from stainless steel surfaces, obviating the need for laborious further purification and associated sample losses. Polyethylene, polypropylene, C8, and C18 surfaces all proved effective at removing contaminants. Scanning electron microscope images of sample surfaces reveal that significantly smaller matrix crystals form on polyethylene and polypropylene surfaces than on stainless steel, C8, or C18 surfaces. Desorption from polyethylene and polypropylene surfaces generates consistently reproducible spectra with better mass resolution than observed for samples desorbed from stainless steel. Improved resolution, combined with reduced intensity of product ion spectra, indicate that peptide and protein molecular ions have less internal energy when desorbed from polyethylene and polypropylene surfaces than from stainless steel. MALDI of contaminated samples can be accomplished by straightforward, on-probe purification, resulting in higher resolution spectra than observed in samples desorbed from stainless steel.