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| Achillea millefolium: yarrow’s volatile oils can be difficult to identify |
Need for quality control to combat adulteration of essential oils
With some of the more expensive essential oils, 90 per cent of those offered
for sale were adulterated, Professor N. Reznicek (Vienna, Austria) told the
symposium. Giving an overview of the methods used to determine the standard
of essential oils, he said that some were mixtures with perhaps more than 100
constituents, where even the minor ones might profoundly influence flavour,
odour or biological properties. Although many classic pharmacopoeial oils, such
as clove and peppermint, were comparatively easy to identify, others such as
that from yarrow (Achillea millefolium) were much more difficult.
Gas chromatography (GC), especially using capillary columns, had made the analysis
of oils much easier, and recent developments in coupling GC with mass spectrometry
had greatly increased the power of identifying constituents, although isomers
could not be distinguished. GC linked with Fourier transform infrared (FT-IR)
spectrometry had now made it possible to distinguish between isomers.
Dr Reznicek then turned his attention to the means by which constituents of
oils could be identified as naturally-occurring or as adulterants through using
endogenous biochemical parameters, particularly the isotope ratio between protons
and deuterium and between carbon-12 and carbon-13. The ratios of these isotopes,
calculated from the mass spectrum, were different for compounds formed in the
plant (being the same for all the natural ingredients in a particular sample)
and for the same compounds made synthetically or obtained commercially from
a different sample of the plant. Further developments in GC, such as enantioselectivity
and the use of cyclodextrins, would further refine the ways in which adulteration
could be detected.