Time-delayed extraction matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of polyacrylnitrile and other synthetic polymers with the matrix­4-hydroxybenzylidene malononitrile

Abstract

Matrix selection and sample preparation technique, namely finding a suitable matrix–analyte combination, has been one of the most important concerns in applying positive and negative ion matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to synthetic polymers. Most matrices used in MALDI have been selected for their sound performance in biopolymer analysis. We evaluated fourteen different matrices for the analysis of polystyrene (non-polar, organic solvent soluble), polymethylmethacrylate (semipolar, organic solvent soluble), polyethyleneglycol (polar, water soluble) and with special emphasis on polyacrylnitrile (semipolar, organic solvent soluble) by UV (337 nm) MALDI-MS employing time-delayed extraction (short fixed delay time of 156 ns). As standard matrix deposition technique we applied the so-called thin layer technique due to the good mass resolution which is obtainable. Among the matrices tested 4-hydroxybenzylidene malononitrile has been found to be the only useful matrix material for all four types of synthetic polymers at 337 nm laser wavelength and the thin layer sample preparation technique. Concerning the characterization of polyacrylnitrile, a difficult but important class of synthetic polymers, 4-hydroxybenzylidene malononitrile turned out to be the only successful MALDI matrix. By applying this matrix in combination with the thin layer preparation technique and time-delayed extraction excellent results in terms of resolution and sensitivity could be obtained in the positive as well as in the negative ion mode. Furthermore, various inorganic salt additives to the matrix 4-hydroxybenzylidene malononitrile were evaluated and the addition of ammonium hydrogen carbonate gave best results for polyacrylnitrile with a low polydispersity. © 1998 John Wiley & Sons, Ltd.