Stationary phase

The chromatographic phase that remains fixed in place while a mobile phase passes over or through it. Differences in how compounds interact with the two phases cause them to separate.

Mobile phase: The liquid or gas that moves through a chromatographic system and carries analytes. It transports compounds past the stationary phase, enabling repeated interactions that produce separation.
Silica gel: A porous, amorphous form of silicon dioxide used as a solid adsorbent. Its surface silanol groups make it a common polar stationary phase.
Reversed-phase chromatography: Liquid chromatography using a nonpolar stationary phase and a relatively polar mobile phase. Its hydrophobic stationary phase retains compounds according to nonpolar interactions.
Liquid chromatography: Chromatography in which a liquid mobile phase carries analytes through a stationary phase. It commonly uses solid supports or immobilized liquids as the stationary phase.
Retention factor: A dimensionless measure of how strongly a compound is retained in chromatography. It quantifies how a compound’s interactions with the stationary phase delay its movement.
Alumina: Aluminum oxide used as a polar adsorbent in chromatography. Its surface chemistry provides an alternative solid stationary phase to silica.
Normal-phase chromatography: Liquid chromatography using a polar stationary phase and a less polar mobile phase. Its polar surface distinguishes compounds through differences in polarity and adsorption.
Gas chromatography: Chromatography in which a gas mobile phase carries volatile analytes through a column. Its stationary phase is commonly a nonvolatile liquid film or a solid adsorbent.
Partition coefficient: The equilibrium ratio of a solute’s concentrations in two phases. It describes how an analyte distributes between stationary and mobile phases in partition chromatography.
Bonded phase: A chromatographic stationary phase made by chemically attaching organic groups to a support surface. Bonded groups tune surface polarity and selectivity, especially in liquid chromatography.

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