MATRIX-ASSISTED-LASER-DESORPTION IONIZATION TIME-OF-FLIGHT MASS-SPECTROMETRY FOR POLYMER ANALYSIS - SOLVENT EFFECT IN SAMPLE PREPARATION/

The success of matrix-assisted laser desorption ionization time-of-fli ght (MALDI-TOF) mass spectrometry for the characterization of polymer structures and for the determination of average molecular weights and distributions depends on the use of a proper sample/matrix preparation protocol. This work examines the effect of solvents, particularly sol vent mixtures, used to prepare polymer, matrix, and cationization reag ent solutions, on MALDI analysis. It is shown that the use of solvent mixtures consisting of polymer solvents does not have a significant ef fect on the molecular weight determination of polystyrene 7000 and pol y(methyl methacrylate) 3750. However, solvent mixtures containing a po lymer nonsolvent can affect the signal reproducibility and cause error s in average weight measurement. This solvent effect was further inves tigated by using confocal laser fluorescence microscopy in conjunction with the use of a fluorescein-labeled polystyrene. It is demonstrated that sample morphology and polymer distribution on the probe can be g reatly influenced by the type of solvents used. For sample preparation in MALDI analysis of polymers, it is important to select a solvent sy stem that will allow matrix crystallization to take place prior to pol ymer precipitation. The use of an excess amount of any polymer nonsolv ent should be avoided. (C) 1998 American Society for Mass Spectrometry .