a study of the quality of a local herbal tea and volatiles of parinari ...

immersed directly into the sample solution and the analytes are transferred directly from
the sample matrix to the extracting phase (Tankeviciute et al., 2004). In SPME headspace
analysis, a fiber is placed in the headspace above the sample (G1Innovations, 2003).
SPME is simple and easy to use and does not require elaborate and expensive instrument
accessories (Hinshaw, 2003). It reduces the time necessary for sample preparation,
decreases purchase and disposal costs of solvents and can improve detection limits
(Vas and Vekey, 2004). It decouples sample from matrix effects that would distort
sample composition or disturb the chromatographic separation (Hinshaw, 2003). The
SPME technique can be routinely used in combination with gas chromatography and
capillary electrophoresis and places no restriction on mass spectrometry (Vas and Vekey,
2004). SPME has also been used with HPLC (Dean, 2009).
2.5.1.3.2 Cold finger molecular distillation
Molecular distillation is also called high vacuum distillation or short path distillation.
This method is used to distil compounds having very high boiling points and which can
get decomposed at high temperatures (Ahluwalia et al., 2005). In flavour analysis,
retention of the full range of volatiles requires low temperature trapping, dry ice-acetone
or liquid nitrogen are useful coolants (Self, 2005). The condensers can also be cooled
with ice water (Reineccius, 1998). In conventional distillation, molecules leaving the
surface of the boiling liquid may undergo many collisions with residual air molecules. In
molecular distillation, all air is removed from the system by vacuum. The condensing
surface is located close to the boiling liquid in such a way that no molecular collisions
take place. The method is particularly useful for distillation of aromatic materials having
a molecular weight between 400 and 1200 and distilling between 50 0 C and 150 0 C
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