Essential Oils

Essential Oils are natural products occurring in plants as secondary metabolites that are highly volatile and exhibit very characteristic smells. They are complex mixtures of hydrocarbons (mainly terpenes), aromatic compounds, aldehydes, ketones, alcohols and esters. Since essential oils are natural products, their quality is largely dependent on the source from which they are derived. This results in a certain range of expected or permitted concentrations for each component to ensure the quality of essential oil used, for example in fragrances and cosmetics, and to detect possible adulteration.

For this reason "Fingerprinting" of plant or food extracts can be valuable in quality control of products as well as in identification of adulterated commercial products. Whereas GC/FID can be a good starting point in these typical tasks, at some point qualitative identification of individual peaks is required. GC/MS with Electron Impact ionisation (EI) fulfils some of the requirements for identification, provided that an adequate EI/MS library is available. Even if these are available however, the mass spectra of isomers of flavour components are often almost identical, library searches need to be complemented by retention time information. In addition, the molecular ion is not always observed in EI/MS spectra, so a secondary confirmation of molecular weight is also desirable.

Analysis of Essential Oils to internationally recognised standards is becoming a more necessary requirement as can be seen by the number of draft ISO standards on the subject, and the list of new monographs of the European Pharmacopoeia from April 2002. This revision also acknowledges the rise of herbal drugs in homeopathic preparations.

As a member of the Essential Oils Sub-Committee of the RSC's Analytical Methods Committee, Butterworth's Frank Judge has enhanced interest and expertise in this area of analysis. This allows him access to some of the latest views on topics, such as the toxicity of certain carcinogenic components of essential oils, and Safrole in oils of Cinnamon and Nutmeg.

For more information on the RSC's latest work, such as "The review of the draft ISO method: Essential Oils" and "Analysis by gas chromatography on capillary chiral column - General Method for the purpose of determining the specific enantiomeric excess or distribution of the chiral compounds contained in the oils", visit the Royal Society of Chemistry website at www.rsc.org.

In addition to the area of "Fingerprinting" by GC-MS, methods of analysis of Essential Oils for QC purposes include: