Elution

Elution is a term used in analytical and organic chemistry to describe the process of extracting one material from another by washing with a solvent (as in washing of loaded ion-exchange resins to remove captured ions).

In a liquid chromatography experiment, for example, an analyte is generally adsorbed, or "bound to", an adsorbent in a liquid chromatography column. The adsorbent, a solid phase (stationary phase), is a powder which is coated onto a solid support. Based on an adsorbent's composition, it can have varying affinities to "hold" onto other molecules—forming a thin film on its outside surface (or on its internal surface if there are cavities within the compound). Elution then is the process of removing analytes from the adsorbent by running a solvent, called an "eluent", past the adsorbent/analyte complex. As the solvent molecules "elute", or travel down through the chromatography column, they can either pass by the adsorbent/analyte complex or they can displace the analyte by binding to the adsorbent in its place. After the solvent molecules displace the analyte, the analyte can be carried out of the column for analysis. This is why as the mobile phase passes out of the column, it typically flows into a detector or is collected for compositional analysis.

Predicting and controlling the order of elution is a key aspect of column chromatographic methods.