eluant

An eluant, also spelled eluent, is the solvent or solvent mixture used as the mobile phase in chromatography to transport analytes through a stationary phase. It dissolves the sample and carries it along the column, with its properties influencing retention times, separation quality, and overall efficiency. The eluant’s polarity, pH, ionic strength, and composition determine how strongly different components interact with the stationary phase.

In liquid chromatography, common eluants include water, aqueous buffers, methanol, acetonitrile, acetone, and mixtures of these solvents. In reversed-phase LC, a polar aqueous or buffered solution is combined with a relatively organic solvent; gradient elution—changing the solvent composition during a run—can improve separation. In normal-phase LC, eluants are typically nonpolar, such as hexane or heptane with small amounts of a polar modifier.

In ion chromatography, eluants are buffered solutions or salt solutions that adjust ionic strength or pH to disrupt interactions between ions and the resin, enabling their elution. In gel permeation or size-exclusion chromatography, eluants are usually buffered liquids that maintain sample stability while allowing size-based separation.

In gas chromatography, the mobile phase is a carrier gas (for example, helium, nitrogen, or hydrogen); the eluent term is less commonly applied in GC, though the concept of a mobile phase remains central to the technique.

Elution is the process by which analytes are carried off the stationary phase by the eluant, yielding separated components for detection and analysis. The term derives from Latin eluere, “to wash out.”