Most compounds, including molecular ions, have absorption bands in the ultraviolet or visible spectral region can be detected by absorption spectroscopy. A mobile phase must be chosen that does not absorb at the wavelength where the analytes are detectable. Some small ionic analytes do not absorb, but they and any ion, can be detected by measuring the conductivity as the mobile phase exits the column. LC columns can also be interfaced with a mass spectrometer. A mass spectrometer can provide a mass spectrum for each chromatographic peak, which helps identify the compound.
Gas chromatography is a chromatographic technique for separating volatile compounds.
A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing the stationary phase, and a detector. Compounds injected into the flowing mobile phase separate as they pass through the column due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column. Mobile phases are generally inert gases such as helium, argon, or nitrogen. The injection port consists of a rubber septum through which a syringe needle is inserted to inject the sample. The injection port is maintained at a higher temperture than the boiling point of the least volatile component in the sample mixture.