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Applications of Supercritical Fluids in Industrial Analysis (Hardcover, 1st ed)
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Applications of Supercritical Fluids in Industrial Analysis (Hardcover, 1st ed)
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the continued search for rapid, efficient and cost-effective means
of analytical measurement has introduced supercritical fluids into
the field of analytical chemistry. Two areas are common:
supercritical fluid chromatography and supercritical fluid
extraction. Both seek to exploit the unique properties of a gas at
temperatures and pressures above the critical point. The most
common supercritical fluid is carbon dioxide employed because of
its low critical temperature (310C), inertness, purity,
non-toxicity and cheapness. Alternative supercritical fluids are
also used and often in conjunction with modifiers. The combined
gas-like mass transfer and liquid-like solvating characteristics
have been used for improved chromatographic separation and faster
sample preparation. Supercritical fluid chromatography (SFC) is
complementary to gas chromatography (GC) and high performance
liquid chromatography (HPLC) providing higher efficiency than HPLC,
together, with the ability to analyse thermally labile and high
molecular weight analytes. Both packed and open tubular columns can
be employed, providing the capability to analyse a wide range of
sample types. In addition, flame ionization detection can be used
thus providing "universal" detection. The separation of complex
mixtures by chromatography provides an effective means of
identifying individual components. However, as with most
techniques, it is the sample preparation which is both time and
labour intensive. Traditionally, Soxhlet extraction has been
employed but this has several disadvantages when extracting
compounds of low and medium polarity using liquid solvents.
Extractions are time consuming,. relatively unselective and use
large amounts of hazardous solvents, so that further cleanup is
usually necessary. Furthermore, after extraction and cleanup steps,
the solution must usually be concentrated by evaporation prior to
introduction into a chromatograph. Supercritical fluid extraction
offers an elegant alternative to the currently applied extraction
procedures. The ability of supercritical fluids to deposit
extractants by simple depressurisation and/or cryogenic focusing
means that solvent concentration can be done quickly and without
heat or vacuum. These latter point are particularly important when
one is seeking preservation of sensitive analytes. This text
therefore seems appropriate at this stage to review the current
situation regarding supercritical fluids in analytical chemistry
and, to consider the future possibilities to which they may be
applied.
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