Principle of chromatography

Differential migration is the key process in chromatography. The compound mixture to be separated is injected into a chromatographic column containing a stationary phase that will retain the compounds (differently according to the structure and the physicochemical properties of each compound), the latter being carried through the column by a mobile phase (an inert gas in GC, an aqueous phase or a solvent mixture in HPLC). The compounds will then migrate differently in the column: the time it takes for a compound to leave the column is called retention time (in the column). A detector placed at the exit of the column detects the molecules of each compound thus separated from the others.