A new interface based on an eluent jet in combination with a conventional gas chromatography momentum separator for use with electron impact mass spectrometry is described. The formation of the eluent jet is based on radio frequency inductive heating. The aerosol formation in the interface is discussed in relation to commercial particle beam (PB) interfaces. The interface is tested in combination with electron impact mass spectrometry using flow injection analysis at flow rates in the range of 5-15 µL/ min commonly encountered in microcolumn liquid chromatography. Electron impact spectra at 1-10-ng levels are found to be comparable with reference spectra. In the single-ion mode, 50 pg of caffeine is detectable with a signal-to-noise ratio of 3:1. Contrary to many other PB systems, linear calibration plots are obtained in the tested range of 3-200 ng of caffeine.In 1984, Willoughby and Browner 1 introduced a new mass spectrometer interface that allowed both electron impact (EI) and chemical ionization (CI) in combination with liquid chromatography (LC). Based on this principle, many commercially available particle beam (PB) interfaces are successfully being used for the analysis of molecules that are not compatible with gas chromatography/mass spectrometry (GC/MS) methods. The systems are based on eluent nebulization, either pneumatical or by thermospray, into a desolvation chamber which is connected to a momentum separator where the high molecular weight analytes are preferentially transferred to the MS ion source, while the low molecular weight solvent molecules are efficiently pumped away. The use of PB interfaces has shown great promise, since the EI spectra obtained contain the fragmentation patterns necessary for unambiguous identification. However, quantitative analysis has been limited by fluctuations in absolute response observed in intraand interday runs and nonlinearity at lower concentrations. [2][3][4][5][6][7][8][9]