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Material Review: Application of Gas-Liquid Chromatography to the Analysis of Essential Oils

Contact Author M.J. Milchard, R. Clery, N. DaCosta, R. Esdale, M. Flowerdew, L. Gates, N. Moss, D.A. Moyler, A. Sherlock, B. Starr, J. Webb, J. Wootten and J.J. Wilson
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GLC fingerprint chromatograms of 12 authentic essential oils were obtained in a collaborative study using the recommended procedure given in Part XVII of this series and are presented here (this paper represents Part XIX). The samples examined were oils of cajuput, eucalyptus, geranium (Bourbon), geranium (Chinese), geranium (Egyptian), lavandin abrialis, lavandin grosso, lavandin super, patchouli (Chinese), patchouli (Indonesian 30 percent), patchouli (Indonesian 35 percent) and thyme. They were selected in consultation with the UK essential oil trade through the British Essential Oil Association (BEOA). The sub-committee gratefully acknowledges the staff time and samples of essential oils provided by the companies involved in this study.

Experimental

Samples of 12 oils together with the NChydrocarbon mixture were distributed to all members of the sub-committee with instructions to prepare standard fingerprint chromatograms for each oil using a methyl polysiloxane non-polar capillary column. Details of the NC-hydrocarbon mixture and its application are given in Part XVII (this paper represents Part XIX).

Each member was asked to submit the chromatograms of the oils and one of the NC-hydrocarbon mixture run at the beginning and at the end of the series. The latter was to check that the characteristics of the column did not change during the exercise. A total of 182 chromatograms were returned. Tables of retention times and percent relative peak areas (area percent) values from the flame ionization detector (FID) for each detected peak accompanied the chromatograms. The identities of the components of interest, usually those accounting for more than 1 percent of the total peak area, were confirmed by two different laboratories using capillary gas chromatography/mass spectrometry (GC/MS) with identities determined by comparison with in-house and commercial mass spectral libraries.2 The relative retention index (RRI) of each peak of interest was calculated relative to the n-alkane series of hydrocarbons run under identical conditions and used to crosscheck the peak identities. The g-pack values were calculated for each column used.

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