AdvancedGasChromatography–Progress inAgricultural, Biomedical and Industrial Applications
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stationaryphasemay consist of particles (porous or solid), thewalls of a tube (i.e. capillary)
or a fibrousmaterial.
Techniques byphysical stateofmobile and stationaryphase:
Chromatography (C); Liquid chromatography (LC); Gas chromatography (GC)
;
Paper
chromatography (PC); Thin-layer chromatography (TLC) Column chromatography (CC)
Gas-liquid chromatography (GLC); Gas-solid chromatography (GSC); Liquid-solid
chromatography
(LSC);
Size-exclusion
chromatography
(SEC);
Liquid-liquid
chromatography (LLC); Ion exchange chromatography
(IEC).
Components separated from the sample are placed in a chromatographic column, a tube in
stainless steel, copper, aluminium or glass for packed chromatography, or quartz for
capillary chromatography. The column contains the stationary phase as a granular porous
solid. The columns are in the oven of the chromatograph, isotherm or temperature
programmed. The mobile phase passes through the column at a constant flow, the flow
values being correlated with the column type (packed, capillary). Thus, a primary
classification couldbegas-solid chromatography andgas-liquid-solid chromatography.
Capillary columns areusedmostly, but not exclusively. They are the latest andbestmethod,
but they cannot replace totally the packed columns. The trends in column chromatography
are:
1.
Packed columns are still used in 20%of chromatographic analysis.
2.
Packed columns are primarily for preparative applications, permanent gas analysis and
samplepreparation.
3.
Packed columns will be used in the future because some applications demand packed
columns not capillary columns.
Gas chromatography has several advantages as a physical method of separating gas
mixtures, namely:
1.
Resolution. The technique is applicable to systems containing components with very
close boiling points. By choosing a suitable stationary phase or adsorbent, molecules
with similar physical and chemical properties could be separated. Sample components
could form innormal distillation, azeotropicmixtures.
2.
Sensitivity. The properties of gas chromatographic systems are responsible for their
widespread use. The detector based on thermal conductivity of the component can
detect picograms of sample. The sensitivity is important considering that a
chromatography test is less than 30minutes. Analysis that typicallyoccurs in about one
hour or more can be reduced to the order of minutes due to the high diffusion rate in
thegasphase and thephase to fast equilibriumbetweenmobile and stationaryphases.
3.
Convenience.Operation ingas chromatography is adirect operation. It does not require
highlyqualifiedpersonnel toperform routine separation.
4.
Costs. Comparedwithmanyother now affordable analytical tools, gas chromatography
presents excellent cost value.
5.
Versatility. GC is adaptable, from samples containing permanent gas up to liquids
havinghighboilingpoints andvolatile solids.
6.
HighSeparationPower. If youusemobilephaseswith a lowviscositydegree, very long
columnswill provide a strong separability
