INSTRUMENTAL EFFECTS IN THE ANALYSIS OF POLYMERS OF WIDE POLYDISPERSITY BY MALDI MASS-SPECTROMETRY

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (to f) mass spectrometry (MS) has been reported to give low number average and weight average molecular weight values for polymers of wide polyd ispersity. Spectra of wide polydisperse polymers more closely resemble the distribution observed by size exclusion chromatography when obtai ned in the reflectron mode. However, the highest mass molecules in the distribution are not observed. These high-mass ions can be observed w hen the more abundant lower mass ions are deflected from reaching the detector. In addition, a mixture of three narrow distribution polymer standards selected to provide a wide mass distribution do not show dis crimination against the high-mass molecules. These results are interpr eted to suggest that the difficulty in observing accurate molecular we ight distributions by MALDI-TOF-MS is at least in part attributable to instrumental limitations rather than ionization limitations. (C) 1997 Elsevier Science B.V.