The impact of buffers and surfactants from micellar electrokinetic chromatography on matrix-assisted laser desorption ionization (MALDI) mass spectrometry of peptides - Effect of buffer type and concentration on mass determination by MALDI-time-of-flight mass spectrometry

This paper describes the effect of various buffers, surfactants, and organi c additives commonly encountered in capillary zone electrophoresis and mice llar electrokinetic chromatography on the molecular weight determination of peptides by matrix-assisted laser desorption/ionization (MALDI) time-of-fl ight mass spectrometry. Signal-to-noise ratio generally decreased with incr easing buffer concentration without affecting mass accuracy, but the type o f buffer was also important. Good spectra were obtained with an ammonium ac etate buffer up to a concentration of 500 mM without impacting ionization o f either peptides or other mobile phase constituents. Ionization of organic additives, such as anionic surfactants, non-ionic surfactants, and cyclode xtrins was buffer dependent and presented a problem when the mass of the ad ditive was in the range of the peptide mass. Brij(R)-35, Tween(R)-80, and c yclodextrins all produced prominent spectra of their own in the presence of sodium or potassium containing buffers, but not with ammonium acetate. Cat ionization of these neutral species with sodium or potassium ions allowed t hem to acquire a positive charge and produce spectra. In contrast, the ammo nium ion appears to be a poor cationizating agent. Ionization of neutral su rfactants was suppressed in ammonium acetate without impacting the spectra of peptides. Ammonium acetate buffers containing 30 mM sodium dodecyl phosp hate also gave spectra with good signal intensity and no interference from the surfactant. Suppression of peptide ionization in MALDI was a problem wh en methanol, tetrabutyl amine, or poly(vinyl alcohol) were used with either ammonium acetate, sodium phosphate, and N-(2-hydroxyethyl)piperazine-N-(2- ethans acid). (C) 2000 Elsevier Science BN. All rights reserved.