A liquid chromatograph/mass spectrometer system which performs enrichment of the sample in the effluent of a conventional liquid chromatograph prior to its being introduced into a differentially pumped quadrupole mass spectrometer is described. The effluent from the liquid chromatograph is concentrated by evaporation of most of the solvent. Solvent evaporation is accomplished by allowing the effluent to flow down an electrically heated wire with the current to the wire controlled by a feedback loop from a volume-sensing photocell. The concentrated effluent flows through a very small needle valve which regulates the flow into and thereby the pressure inside the mass spectrometer. The valve is constructed such that liquid is sprayed into the ion source of the mass spectrometer. The application of the system to polynuclear aromatic hydrocarbon characterization and to quantitation of phenolic compounds in alternate fuels is shown.