Mass spectrometry has become a viable technique for characterization of low molecular weight synthetic polymers. The power of this method compared to more classical techniques of polymer analysis is the fast and accurate determination of the absolute molecular weight distribution. Moreover, data on the sequence of repeat units, polymer additives and impurities, and structural information can be obtained.1 The main barriers for mass spectrometry of high molecular weight compounds, caused by the low volatility and/or thermal lability of those substances, have been overcome to a considerable extent by the development of soft ionization techniques. Secondary ion mass spectrometry (SIMS) in combination with time-of-flight (TOF) mass analyzers has been used for molecular weight determination of polymers in the mass range m/z 500-10 000 Da, mainly from thin films.2•3 Beside desorption of intact oligomer ions, fragmentation of the polymer chain is observed. Molecular weight distribution of oligomers has also been obtained by field desorption (FD),4•5 fast atom bombardment,6 electrohydrodynamic,7•8 plasma desorption,9 and electrospray ionization mass spectrometry.10 Whereas C02-laser desorption, combined with either a time-of-flight or a fourier-transform mass analyzer, yields abundant molecular ion peaks for a number of polymers in the mass range up to 10 000 Da,11•12 UV-laser desorption was limited to polymer masses of 1000 -2000 The accessible mass range has been considerably extended by the development of the matrix-assisted laser desorption/ionization (MALDI) technique.15•16 Sample mol-

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A laboratory prototype is described of a new ICP-MS system with high mass resolution, based on a double focusing magnetic field analyser, which has been especially designed for application in elemental analysis. The performance characteristics of this instrument are summarized comparing operation in a low resolution mode (R=300) and a high resolution mode (R=3000) with reference to common quadrupole instruments with (nearly) unit resolution. Most of the typical spectral interferences can be resolved. Detection limits were achieved of one order of magnitude and more below those obtained with quadrupole instruments. Several operational features of the instrument are described.

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