Glossary of HPLC/LC Separation Terms

Feb 01, 2008


Ronald E. Majors
In 2001, the second glossary of common and not-so-common terms and "buzz words" for reference to high performance liquid chromatography (HPLC) columns and column technology was published (1). It is time for an update as new terms have arisen or, in some cases, their original meanings have expanded or changed. We have also decided to expand the terms dealing with HPLC and LC to cover some of the common terms that we neglected to include in the earlier glossary. To make room for this expansion, we have decided to remove most of the terms referring to capillary electrophoresis (CE) because this technique is rather specialized and not all liquid chromatographers are also performing the various forms of CE. We will also stick to the conventions of the International Union of Pure and Applied Chemistry (IUPAC) in their "Nomenclature for Chromatography" that provides guidance and changes in some of the more commonly accepted terms (2). Because there is still widespread usage of nomenclature that is not in alignment with the IUPAC definitions, those terms specifically recommended by them will be followed by a (IUPAC) in parentheses.




The article is not intended to be an in-depth listing or highly theoretical coverage. For example, we have elected not to cover the myriad of terms used in instrumentation, detection, data handling, and validation associated with HPLC analysis but have chosen to use terms that may be encountered in everyday laboratory work around columns, phases, method development, and general usage. The listing should be helpful to those just starting in HPLC but it also can serve as a refresher for long-time users in the field.

The entire listing, including the removed CE terms, also canbe found on the LCGC website at http://www.chromatographyonline.com/.

A

α: See separation factor.

A solvent: Usually the weaker solvent in a binary eluent or gradient elution separation. In reversed-phase liquid chromatography (LC), the A solvent typically is water or a water-rich mixture.

A term: The first term in the van Deemter equation. See eddy dispersion term and van Deemter equation.

Absorption: The process of retention in which the solute partitions into a liquid-like coating.

Activity: The relative strength of the surface of the packing in adsorption chromatography. For silica gel, the more available the silanol groups, the more active the surface. Activity can be controlled by adding water or other polar modifier that hydrogen bonds to the active sites, thereby reducing the surface activity.

Adapter: A union with different threads on each end; generally used to connect two different types of tubing together.

Additive: A substance added to the mobile phase to improve the separation or detection characteristics; for example, a competing base to negate the effects of silanols, a chelating agent to block metal sites, or a UV-absorbing compound to perform indirect photometric detection.