Extraction Technologies For Medicinal And Aromatic Plants - Unido

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
Figure 3: Static headspace trapping technique
9.5.2 Dynamic Headspace Trapping
In this technique (Figure 4), the sample is continuously purged
with an inert gas (the purge gas), until all volatile compounds are removed.
During this step, the gas effl uent leaving the sample vessel is conducted
through a trap, either cooled to low temperature or containing an adsorbent.
This trap retards the volatile analytes purged from the sample. When gas
extraction is complete, the condensed or adsorbed analytes by rapid heating
of the trap now get purged with the carrier gas.
In Figure 4, the desorbed analytes are conducted directly into
the gas chromatograph. Thermal desorption from an adsorbent is not instantaneous:
thus, the sample “slug” might be too long, creating broad peaks,
with tailing. This is particularly the case when a capillary column is used in
the gas chromatograph. For this reason, usually a second, small trap, cooled
to low temperature, is placed in the carrier gas line between the primary trap
and the column. When desorption is fi nished, this small trap is then heated
very rapidly: in this way, a sharp band of the analytes enters the column.
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