Page 14 - Illustrated Pocket Dictionary of Chromatography

ALKANES 7

column determine, in conjunction with other operational parameters
(mobile phase composition, temperature, etc), the degree to which an
analyte is retained on the stationary phase.
aerogel A packing material that is produced from a gel that con-
tains a dispersing liquid. The dispersing liquid is removed, leaving a
porous gel. The silica-based form of these gels is commonly used for
size-exclusion work.
affinity chromatography An LC technique that uses various bio-
logically active substances (e.g., enzymes, substrates) to generate sep-
arations, for example, the use of antibodies bonded to the support that
interact specifically with a corresponding hormone (drug or peptide,
etc). The difficulty with affinity chromatography is in finding condi-
tions where the substrate-enzyme interactions are reversible on a
chromatographic timescale. In addition, for bonded enzymes loss of
activity on bonding to the surface and maintaining conditions (both
use and storage) for long-term separation reproducibility are a
challenge.

affinity ligand A material bonded to a support to generate a
separation based on affinity interactions. Affinity ligands can be for
general substance classes such as lectins (e.g., concanavalin A) for
sugars and polysaccharides, dyes (e.g., Cibacron blue) for specific
enzyme classes, or biospecific ligands such as an antibody for an
antigen.

agarose A polymeric polysaccharide used in the separation of bio-
molecules in both slab electrophoresis and gel-filtration separations.

air peak In GC a nonretained, nonexcluded component (typically
air) is used to define the minimum time needed for to travel from the
injector to the detector. (This is similar to the void volume in LC
systems.)
alkanes A class of compounds that are saturated hydrocarbons.
The general formula of a linear alkane is C nH 2n+2. Alkanes may also
have branched or cyclic structures. Examples of alkanes frequently
used in chromatographic separations are pentane, hexane, and
heptane (linear alkanes where n = 5, 6, and 7, respectively), iso-octane
(a branched alkane also called 2,2,4-trimethylpentane), and cyclopen-
tane and cyclohexane (cyclic alkanes having rings of 5 and 6 carbons,
respectively).