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Application of Gas-Liquid Chromatography to the Analysis of Essential Oils

By: NJ Milchard et al.
Posted: June 30, 2010, from the June 2010 issue of P&F magazine.

As a part of a collaborative study, samples of the six oils together with the NC-hydrocarbon mixture were distributed to members of the subcommittee (of the analytical methods committee, RSC, London) with instructions to prepare a standard fingerprint chromatogram of each of the oils using a methyl polysiloxane non-polar capillary column. Details of the NC-hydrocarbon mixture and its application are given in Part XVII.1 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 ensure that the characteristics of the column did not change during the exercise.

A total of 36 chromatograms were received, along with the retention times and percentage relative peak areas (area %) and values from the flame ionization detector (FID) for each detected peak. The identities of the components of interest, usually those accounting for more than 1% 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. 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 cross-check the peak identities. The g-pack values were calculated for each column used.

It was noted that 1,8-cineole and limonene were not completely resolved on the methyl polysiloxane non-polar column at certain relative concentrations. In these cases, the oils were examined on a polar column and the relative proportions were used to determine their contents on the non-polar column.

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