How is the sample introduced into the mass spectrometer?

      For reasonably pure solids the sample can be placed on the tip of a rod that is inserted into the evacuated source region through a vacuum-tight seal. The sample is then evaporated or sublimed into the gas phase, usually by heating. Gases and liquids can be introduced through specially designed inlets with controlled flow.The gaseous molecules are then ionized (often with accompanying fragmentation) and the ions are mass analyzed. In some special techniques, volatilization and ionization occur at the same time.

      To obtain the mass spectrum of a single compound in a mixture, the individual components must be separated prior to analysis by mass spectrometry. Separation is necessary for unambiguous identification because two compounds present in the source region simultaneously create an overlapping or mixed spectrum and even simple compounds can generate many fragment ions. Since the 1960's gas chromatography (GC) has been coupled to mass spectrometry. This connection allows compounds already in the vapor phase to enter the mass spectrometer separated in time so that the components of mixtures can be detected and analyzed sequentially. More recently, liquid chromatographs, supercritical fluid chromatographs, and capillary elctrophoresis devices connected to mass spectrometers have been used to separate components of complex mixtures prior to mass analysis.