Gas Chromatography - Tandem Techniques - Modern GC/IR Systems > Light Pipe Interfaces > Page 49

Another typical example of the use of the GC/IR instrument is for the analysis of the essential oils of basil a chromatogram of which, is shown in figure 37. A sample of the oil was obtained by supercritical fluid extraction. Superfluid extraction is often used to obtaining samples of essential oils from botanical tissue. The technique is popular due to it being chemically 'gentle' and rarely causes thermal degradation of labile materials. The herb basil was extracted with liquid carbon dioxide at 60ūC and at 250 atmospheres pressure. The extract (a solution of the essential oil in liquid carbon dioxide) is decompressed through a length of silica capillary into an appropriate solvent. Alternatively, it could be trapped on a suitable adsorbent contained in a packed tube, and then thermally desorbed into the carrier gas of a gas chromatograph. The column that was used in this example was a macro-bore open tubular column, 50 m long, 0.32 mm in diameter carrying film of a methyl silicone a 5 mm thick. The chromatogram was obtained by plotting the integrals of each adsorption curve against time.