• The attraction may be hydrogen bonding or van der Waals forces

• In some cases the attraction may be a chemical reaction

• In biochemistry, the difference often is that some components of the mixture will fit into pores in the column material whereas others will not; this is size-exclusion chromatography.

A Cartoon of a Liquid Chromatograph
A Cartoon of a Gas Chromatograph

Detectors in liquid chromatography may use changes in refractive index, UV-VIS absorption, or conductance to determine when a component of the mixture is leaving the column. Gas chromatograph detectors typically changes in thermal conductivity, or generate ion currents by burning the exiting components in a flame. The latter is called a flame ionization detector.

In either case, the output of the instrument is a graph of the property measured against time. The length of time it takes a component to exit the column is called its retention time, and can be used to help identify the component.