According to “Chromatography Composition Measurement,” in The Measurement, Instrumentation, and Sensors Handbook, chromatography is a technique for separating mixtures into their components. The process involves two phases. The first phase is stationary and provides a large surface area. The second phase is mobile and moves in a fixed direction relative to the stationary phase.
Modern chromatography uses a solid or liquid for the stationary phase and liquid or gas for the mobile phase. Gas and liquid chromatographs provide the two major classifications of tools but there are subclassifications including gas-liquid chromatography (GLC), gas-solid chromatography (GSC), liquid-solid chromatography (LSG) and liquid-liquid chromatography.
Principle processes for a continuous interchange of molecules between the mobile and stationary phases include adsorption, liquid-liquid partition, ion exchange and size exclusion. Liquid chromatography may involve all four process but gas chromatography predominantly uses adsorption.
A gas chromatograph consists of over a dozen different elements to provide analysis.
The 10.8 cm x 13.3 cm x 19.1 cm Vernier Mini GC demonstrates advances of modern gas chromatographs including portability and the ability to use room air as the carrier gas.
To enhance the diagnostic capabilities, the separation power of chromatography is often combined with other analysis techniques (specifically, spectrometry for identification) to obtain the benefits of both. Common combinations include gas chromatography-mass spectrometry (GC-MS), gas chromatography-infrared spectrometry (GC-IR) and liquid chromatography-mass spectrometry (LC-MS). GC-IR is three to four orders of magnitude less sensitive than GC-MS but the techniques are in some respects complementary. In fact, GC-IR-MS can be sued for analyzing complex mixtures. GC-MS is a well-established technique with LC-MS increasing in its popularity.