Extraction Technologies for Medicinal and Aromatic ... - Capacity4Dev

EXTRACTION TECHNOLOGIES FOR MEDICINAL AND AROMATIC PLANTS
Figure 1: The SPME device
If the sample is in a vial, the septum of the vial is fi rst pierced
with the needle (with the fi ber in the retracted position), and the plunger is
lowered, which exposes the fi ber to sample. The analytes are allowed to
partition into the coating for a pre-determined time, and the fi ber is then
retracted back to the needle. The device is then transferred to the SPME
instrument. When gas chromatography is used for analyte separation and
quantifi cation, the fi ber is inserted into a hot injector, where thermal desorption
of the trapped analyte takes place.
For spot sampling, the fi ber is exposed to a sample matrix until
partitioning equilibrium is reached between sample matrix and the coating
material. In the time average approach, on the other hand, the fi ber remains
in the needle during exposure of the SPME device to the sample. The coating
works as a trap for the analytes that diffuse into the needle, resulting in
integral concentration over time measurements.
SPME sampling can be performed in three basic modes: direct
extraction, headspace trapping, and extraction with membrane protection.
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