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Terpene composition of essential oils


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Ayling, Geoffrey Mervyn 1976 , 'Terpene composition of essential oils', Unspecified thesis, University of Tasmania.

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A review is given of techniques for sampling,
extraction, separation and analysis of essential oils, and
the effects of each upon the finally determined essential
oil composition. It is concluded "that presently~available
techniques such as steam-distillation, solvent extraction,
vapour trapping and even solid-sampling gas chromatographic
injection procedures impose so many characteristic effects
upon the volatile terpenoids in a plant sample, that it is
not practicable to obtain instantaneous measurement of volatiles
as they are released to the atmosphere. In addition, many of
the well-known techniques and approaches to essential oil
analysis lead to many losses and artifacts, and are so
protracted as to mitigate against the feasibility of a routine
analytical procedure for use in a survey of essential oils.
A recommended routine analytical procedure was
developed for use in surveys of essential oils, and its
effectiveness is illustrated by the analysis of essential
oils from 7 endemic Tasmanian plants.
Details are given of the development of syringe-headspace
gas chromatographic analysis, which is a novel
method of identifying and monitoring components in vapours
from comminuted plant tissue as they are released to the
atmosphere at room temperature. The syringe-headspace
technique is recommended as a means of directly using verified
plant species from a botanical gardens as a source of
reference terpenes, which otherwise may be too unstable to
be stored as pure compounds. This technique allows the
relative retention time of an authentic terpenoid to be
measured in plant material for direct comparison with that
of an unidentified compound. It thereby enables the worker
to justify spending considerable effort in synthesizing,
isolating or purchasing the suspected terpenoid.
Successive injections of vapour from a single sample
of comminuted foliage, by the syringe-headspace technique,
often exhibit changes in the proportions of some components
with respect to one another. Such changes were observed
between terpenoids having a common hypothetical precursor
according to the biosynthetic scheme by Ruzicka. This
technique is a novel means of directly measuring biosynthetic
changes. It considerably extends the usefulness of Zavarin's
earlier advocated procedure for utilizing 'quantitative
co-occurrence', which is a basically different procedure to
supplement the results of tracer studies.
Both the routine analytical procedure for analysis
of essential oils, and the syringe-headspace technique were
used to compare the compositions of terpenoids in 19 species
of conifer susceptible to attack by the Woodwasp, Sirex
noctilio. An investigation was also made of earlier inferred
changes in the compositions of essential oils following the
wounding of trees of Pinus radiata. Widely varying compositions
are reported for the first time for oils distilled from bark of
felled.trees. Variations in oil composition from a single
injured tree trunk ranged from 15.7 to 20.3 percent a-pinene,
54.8 to 68.2 percent 8-pinene, 9.0 to 18.3 percent limonene
and 2.5 to 6.7 percent myrcene. The range of compositions
of oils from within and between trees of a species was very
wide, so that in a comparison of each species, no single
insect-attractive optimum composition could be envisaged.
It appeared more likely that S. noctilio could be attracted to
one of the 'temporarily-released' components which appeared to
cause qualitative changes in many oils.

Item Type: Thesis - Unspecified
Authors/Creators:Ayling, Geoffrey Mervyn
Keywords: Terpenes, Essences and essential oils
Copyright Holders: The Author
Copyright Information:

Copyright 1976 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Sc.) - University of Tasmania, 1977. Includes bibliographical references

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