Eluenten

Eluenten, in chromatography, refer to the mobile phase—the solvent or solvent mixture that moves through the stationary phase and carries the sample for separation. The choice and composition of an eluent determine how analytes interact with the stationary phase, and thus how they are separated.

Eluenten are used in various chromatographic techniques, including thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). In TLC, of which the plate is developed by the rising eluent, the solvent system sets the separation of components. In HPLC, the eluent is a liquid that can be run isocratically (constant composition) or as a gradient (changing composition) to improve peak resolution. In gas chromatography (GC), the term eluent is less common; the mobile phase is typically a carrier gas such as helium or nitrogen, which fulfills a similar transport role.

The selection of eluents depends on several factors. Polarity and solubility influence how well analytes partition between the mobile and stationary phases. pH and ionic strength are important for ionizable compounds, while volatility and viscosity affect detector compatibility and system performance. Eluent strength describes a solvent’s ability to elute analytes and often guides decisions about gradient versus isocratic operation. Compatibility with the stationary phase and the detector is essential, as is the need for low UV absorbance or MS compatibility when using certain detectors.

Common eluents include water, methanol, acetonitrile, isopropanol, ethyl acetate, dichloromethane, and hexane, or mixtures thereof. In practice, eluents are carefully prepared to maximize separation efficiency, reproducibility, and detector suitability, while considering safety and environmental factors.