Glossary of HPLC Terms

 

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Activity

In adsorption chromatography, this is the relative strength of the surface of the packing. For silica gel, the

more exposed the silanol groups, the more active the surface. Activity can be controlled by adding water

or another polar modifier, which is hydrogen bonded to the active sites, thereby reducing the surface

activity.

Adsorbent

Packing used in adsorption chromatography. Silica gel and alumina are the most frequently used

adsorbents in HPLC.

Adsorption

The process of interaction between the solute and the surface of an adsorbent. The forces involved can

be strong such as hydrogen bonds, or weak such as van der Waals forces. For silica gel, the silanol group

is the driving force for adsorption, and any solute functional group that can interact with this group can be

retained by liquid-solid chromatography on silica.

Adsorption chromatography

One of the basic LC modes which relies on the adsorption process to effect the separation. Silica gel and

alumina are the most frequently used supports. The molecules are retained by the interaction of their

polar functional groups with the surface functional groups such as silanols of silica.

Adsorption isotherm

In adsorption chromatography, this is a plot of the equilibrium concentration of sample in the mobile

phase per unit volume verses the concentration in the stationary phase per unit weight. The shape of the

adsorption isotherm can determine the chromatographic behavior of the solute such as tailing, fronting,

and sample overload.

Affinity chromatography

A technique in which a biospecific adsorbent is prepared by coupling a specific ligand (such as an

enzyme, antigen, or hormone) for the macromolecule of interest to a solid support (or carrier). This

immobilized ligand will interact only with molecules that can selectively bind to it. Molecules that will not

bind elute unretained. The retained compound can later be released in a purified state. Affinity

chromatography is not a chromatographic technique but selective filtration.

Alumina

An adsorbent sometimes used in adsorption chromatography. Aluminum oxide (AI203) is a porous