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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 socalled 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. Received 15 May 1998; Accepted 3 July 1998 Since the development of matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) this technique has been successfully used for the molecular weight determination of large biopolymers, especially proteins.

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ions, while unusual for biopolymers in PDMS, has been found as a normal feature in the PD mass spectra of calixarenes. In the positive-ion mode strong fragmentation was observed which provided structural information. The negative-ion mass spectra exhibited, in all cases, [M-H] -ions but less fragmentation was found compared with the positive-ion mode. For compounds (5-9) carrying an ester group the loss of an acyl group generated intense fragment ions. Samples have been prepared by the spin deposition technique on plain aluminium covered targets, on nitrocellulose covered targets as support and 3-(3-pyridyl) acrylic acid covered targets as matrix resulting in different molecular/fragment ion abundances.