Section F – Combined techniques
F4 GAS CHROMATOGRAPHY-
INFRARED SPECTROMETRY
Principles Chromatographic techniques (Section D) are used for the separation of multi-
component mixtures. However, identification of the separated solutes by their
retention times alone is often ambiguous. Infrared spectrometry (Topics E10 and
E11) is a very powerful and versatile technique for the identification of func-
tional groups. The newer instruments, using computerized Fourier transform
(FT) processing of spectral information, are readily interfaced with gas
chromatographs using heated transfer lines and gas cells which facilitate the
rapid detection and identification of unknown compounds.
Instrumentation The choice of gas chromatographyrequires that the components must be
volatile enough to pass through the chromatographic column and sufficiently
different in properties to be resolved by the stationary phase. In a simple case, a
difference of a few degrees in the boiling point is enough to give separation. All
the many columns, stationary phases, gases and temperature programs
described for GC can be adapted for use with GC-FTIR.
The choice of column is important. The greater sensitivity of modern FTIR
systems and improvements in design have allowed the use of capillary columns,
which produce sharper peaks. Typically, a 30 m long, 0.3 mm diameter fused
silica column coated with a 1-mm thickness of stationary phase may be
Key Notes
The use of chromatographic techniques to separate mixtures is one of the
most important analytical tools. The separated components may be
classified by their retention times, but other techniques should be used to
aid identification. Infrared spectrometry is capable of establishing which
functional groups are present in the separated components.Combining gas chromatography with infrared spectrometry involves
passing the solutes in the carrier gas stream through a heated infrared
gas cell positioned in a rapid scanning Fourier transform spectrometer.Gas chromatography-Fourier transform infrared spectrometry has been
employed in the analysis of biological materials such as fragrances, to
determine the proportions and nature of each component, of solvents to
determine their purity and composition, and to identify the evolved
products when substances are degraded by heating.Related topics Gas chromatography: principles and Infrared and Raman spectrometry:
instrumentation (D4) principles and instrumentation
Gas chromatography: procedures and (E10)
applications (D5) Infrared and Raman spectrometry:
applications (E11)PrinciplesInstrumentationApplications