The combination of a gas chromatograph with a time-of-flight mass spectrometer has proved to be extremely useful for the rapid and positive identification of unknowns in complex mixtures. The mass spectra of the components can be scanned and recorded simultaneously with the running of the chromatograph. A getter-ion pump has been used successfully to maintain the high vacuum in the spectrometer. This provides a clean system with little background. The input system to the spectrometer is designed to trap the sample from the column and allow it to leak into the spectrometer long enough to allow the analog output system to record the spectrum. This normally requires less than 1 minute. Usable spectra can be obtained of components in very low concentrations (0.1 p.p.m.) and even when they are only partly resolved by the chromatograph.