The limits of performance of a linear time-of-flight mass spectrometer using matrix-assisted laser desorp tionlionization have been tested. Effects of the pressure in the vacuum system and the sampling rate of the digital oscilloscopes on mass resolution have been investigated. Spectra recorded at different pressures and at sampling rates of 100 MS s-', 400 MS s-' and 1 GS s-' are compared. A mass resolving power m/Am (full width at half maximum) of 900 to 2400 has been achieved for a selection of peptides and proteins within a mass range from 800 to 6000 Da.

Different halocyclopropanes prepared by cycloaddition of halocarbenes to olefins by phase-transfer reactions have been analyzed by gas chromatography/mass spectrometry (GUMS). Starting from CCI,-adducts, the investigations have been extended to bromine-and fluorine-containing cyclopropanes. As reaction partners, a group of olefins, containing different alkyl substituents, have been selected. Thereby, special attention has been paid to smooth reaction conditions, high reaction yield and simple handling. The suitability for mass spectral analysis is discussed. Fragmentation pathways and diagnostic potential are evaluated. Best results have been obtained by addition of bromofluorocarbene to double bonds. The resulting bromofluorocyclopropanes are considered to be the most promising derivatives for mass spectral localization of double bonds.