Chromatography separates the components of a mixture by allowing them to move at different rates through a system containing a mobile phase and a stationary phase.
Two phases, different roles
Mobile phase: the fluid that travels through or across the stationary phase, carrying components of the mixture. It can be a liquid or a gas.
Stationary phase: the material that remains fixed as the mobile phase moves through the system. It may be a solid, or a liquid supported on a solid.
The components do not divide their time equally between the two phases, so they travel through the chromatographic system at different rates.
Basic principle
Phases in the main chromatography techniques
| Technique | Mobile phase | Stationary phase |
|---|---|---|
| Thin-layer chromatography (TLC) | Liquid solvent | Solid silica or alumina coating |
| Column chromatography (CC) | Liquid solvent | Solid silica or alumina |
| Gas chromatography (GC) | Inert carrier gas | Solid, or a liquid coating supported on a solid |