OBSERVATION OF VARYING MOLECULAR-WEIGHT DISTRIBUTIONS IN MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME-OF-FLIGHT ANALYSIS OF POLYMETHYL METHACRYLATE/

The molecular weight distribution of a polymethyl methacrylate (PMMA 4 K) standard was subjected to matrix-assisted laser desorption/ionizati on time-of-flight (MALDI-TOF) mass spectrometric analysis. It was obse rved that the molecular weight distribution measured by MALDI-TOF coul d vary by as much as 27% even with a nearly same set of experimental p arameters, and that this variation was due to mass discrimination agai nst larger PMMA oligomers. Results indicate that the observed mass dis crimination resulted mainly from the MALDI sample preparation and that a systematic study of the effects of sample preparation of MALDI-TOF analysis of polymers is needed to minimize potential mass discriminati on. A brief explanation for the mass discrimination is also given. (C) 1997 by John Wiley & Sons, Ltd.