MATRIX PERFORMANCE IN MATRIX-ASSISTED LASER DESORPTION IONIZATION FORMOLECULAR-WEIGHT DETERMINATION IN SIALYL AND NON-SIALYL OLIGOSACCHARIDE PROTEINS/

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry relies on the formation of intact molecular ions to determine molecula r weight. In biochemical research, conventional methods of protein ana lysis at picomol to fentomol sensitivity, such as sodium dodecyl sulph ate polyacrylamide gel electrophoresis, have been replaced by this new ionization method. Unfortunately, problems caused by the mass accurac y and low resolution restrict the use of this ionization technique, pa rticularly when a high mass accuracy in a high mass range is required. In this paper it is shown that the appropriate choice of parameters w hich determine the desorption/ionization of glycoproteins can improve the quality of MALDI mass spectra as well as mass reproducibility and resolution. The study of sample-matrix solution composition, pH and in strumental conditions allow the molecular weight determination of high ly glycosylated proteins with a high percentage of sialic acid, e.g. e rythropoietin. The glycosylation of this molecule which interferes wit h the production of multiply charged ions in electrospray ionization d oes not affect the desorption/ionization in MALDI analysis. We report the best operating conditions used to establish the degree of heteroge neity of erythropoietin. (C) 1997 by John Wiley & Sons, Ltd.