Page 160 - Illustrated Pocket Dictionary of Chromatography

R

racemate Equal parts of the (+) and (-) forms of enantiomers
result in a racemic mixture. These mixtures do not polarize light as a
pure enantiomer would.

radial compression The technique of radial compression is used
on columns that are fabricated with flexible walls. Application of the
radial pressure minimizes wall effects during the separation and
thereby decreases peak broadening and increases overall operational
efficiency.
radial thin-layer chromatography A TLC technique that spots
a sample in the center of a circular plate. Developing solvent is applied
to the spot through a wick. The sample is carried out radially from
the center spot as the solvent moves away from the wick.

radioactivity detector Used in HPLC to monitor radioisotopi-
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13
cally labeled analytes (e.g., H, 131 I, C). The decay mechanism of
the atom determines the type of detector that is used. For example,
b-decay atoms can be detected directly through b-radiation or indi-
rectly through scintillation derived from the disintegration event. The
cells for this type of detector are typically quite large (or fractions
need to be collected), and so the overall efficiency of the system is
low.

Raman scatter The scatter/emission of exciting wavelengths at
fixed energy differences. This scatter produces background signal for
fluorescence analyses.

random errors Those uncertainties that are part of a result
because of sampling and testing variability.

range The upper and lower limits for analyte concentration for
which a detector gives an acceptable response. The range is deter-
mined by the operational requirements set by the analyst for the
method; it is always equal to or greater than the working range.

Illustrated Pocket Dictionary of Chromatography, by Paul C. Sadek.
ISBN 0-471-20021-2 Copyright © 2004 John Wiley & Sons, Inc.
161