Page 165 - Academic Press Encyclopedia of Physical Science and Technology 3rd Analytical Chemistry

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Encyclopedia of Physical Science and Technology EN006F-275 June 29, 2001 21:12

456 Gas Chromatography

TABLE I Comparison of Types of Chromatography
Mobile Types of
phase Stationary phase chromatography a Abbreviation Separation
Liquid Solid Liquid–Solid LSC b Adsorption
Liquid Liquid (immiscible) Liquid–Liquid LLC Solubility (partition)
Gas Solid Gas–Solid GSC Adsorption
Gas Liquid Gas–Liquid GLC Solubility (partition)
a Gas–gas and solid–solid equilibria do occur in nature; however, they are impractical for chromato-
graphic separations.
b C = Chromatography.

chromatography were discovered by a Russian botanist (a decade later, recognized by a Nobel Prize in Chem-
M. S. Tswett (1872–1919) but hardly developed into use- istry). Several investigations pertaining to the use of gas
ful chemical separation procedures until the 1930s. The as the mobile phase in gas/adsorption systems were re-
name chromatography was originated by Tswett who ported in Austria, Czechoslovakia, Russia, and Sweden
primarily investigated plant pigments (chromatos is the during the 1940s. However, the development of gas–liquid
Greek name for color). However, any method that utilizes chromatography, reported in 1952 by A. T. James and
a distribution of the molecules to be separated between the A. J. P. Martin, is widely considered the beginning of GC
mobile phase (a gas or a liquid) and the stationary phase (a as a powerful analytical method.
solid or a liquid that is immiscible with the mobile phase) Today, GC is complementary to other separation meth-
now qualifies as chromatography. The physical state of ods. It can be practiced on either a small (analytical) scale
the mobile phase determines whether we deal with gas or or a large (preparative or industrial) scale. The prepara-
liquid chromatography. tive uses of GC are relatively uncommon. While typical
Variation in the type of stationary phase is important as amounts of chemical substances analyzed by the modern
well: if a solid is used as the stationary phase, the inter- GC are between the microgram (10 −6 g) and nanogram
action of the molecules under separation with it is due to (10 −9 g), samples as small as a femtogram (10 −15 g) can
adsorption forces; if a liquid is used in the same capacity, be measured in special circumstances. Importantly, con-
the molecules under separation interact with it based on temporary GC can often simultaneously recognize up to
their solubilities. According to this type of interaction, we several hundred chemical substances.
distinguishbetweenadsorptionchromatographyandparti-
tion chromatography. This classification is further evident
in Table I. II. PHYSICAL PRINCIPLES
Tswett’s original work pertained to liquid adsorption
chromatography, while the first experiments on liquid par- The apparatus designated to separate compounds by GC
tition chromatography were described in the early 1940s is called the gas chromatograph. Its essential parts are
by A. J. P. Martin and his co-workers in Great Britain shown in Fig. 1. At the heart of the system is the separation

FIGURE 1 A gas chromatograph with its main components.