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For several years now, the rise in mass spectrometry has favoured the use of the coupled GC/MS technique, which consists in connecting the chromatograph to a mass detector (a low‐resolution mass spectrometer, see Chapter 16 for more details). Its use as a universal detector for capillary GC has the advantage of leading to a fragmentation spectrum of each eluted compound and, therefore, to their identification when using the spectral libraries. There are several types of interfaces between the chromatograph and the mass spectrometer. The most developed ionization mode is electron impact (EI). From the total ion current (TIC), a chromatogram can be plotted which represents all of the compounds eluted. By choosing a particular ion (selective ion monitoring, or SIM), a selective chromatogram can be produced. This method has become essential, notably in the context of environmental studies. Nevertheless, it requires the use of high‐performance columns (ID = 0.1–0.2 mm) with no bleeding.