Analysis of essential oils

Several techniques and criteria are used for the assessment of the quality of essential oils. These are  

Sensory evaluation is carried out by the use of sensory organs and most importantly by the nose. It is considered crucial for the acceptance of an essential oil in perfumery houses. A perfumer or a panel of fragrance experts often have the last word on the acceptance criteria however, their assessment should be verified and documented by experimental proof [1, 2, 4, 5, 69-73]. 

Physicochemical tests are required in essential oil monographs published in standards, pharmacopoeias and codices. Chromatospectral techniques are modern methods used to assess the quality of essential oils. The most important technique for the analysis of essential oils is GC. Several detectors may 

MDGC is useful for separating compounds of an essential oil using two columns in line with different polarities. Through column-switching techniques, selected impure compounds in the first column can be diverted to the second column to ensure their complete separation. If the second column is chiral, then enantiomers potentially can be separated. The selected chiral stationary phase affects the resolution and separation drastically [73]. 

GC/isotope ratio MS and site-specific natural isotope fractionation deuterium NMR spectroscopy are useful more recent tools for detecting sophisticated adulterations [3-5]. 

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For further details on the separation of geraniol and citronellol the chapter on the analysis of essential oils should be consulted. 

In general, the analysis of essential oils merely involves the application of the ordinary principles of analytical chemistry to this special group of bodies, which possess many features in common. Of course, many special processes have to be used in certain cases, to which attention will be drawn where necessary. The present chapter will be devoted to the details of a few methods which are in very common use in the analysis of these bodies, and which are absolutely necessary in order to form an opinion on the purity of very many oils. Particular processes are mentioned as required under the essential oils or compounds concerned. These remarks may be prefaced by saying that the obtaining of the results of an analysis of an essential oil is not always as difficult a matter as the interpretation of the same when obtained. 

Benedikt and Grussner have proposed the determination of the methyl number in the analysis of essential oils. Whilst this process may have some vaAue in the examination of the constitution of a compound, it is very rarely necessary to use it in the analysis of essential oils. The methyl number (which is a somewhat fallacious term as it includes other Alkyl radicles) is understood as the number of miUigrams of methyl yielded by the gram of the substance when heated with hydriodic acid. From 0 2 to 0 3 gram of the oil is heated with hydriodic acid of specific. gravity 1 7 and the methyl iodide formed collected in a suitable receiver,... 

In bringing the second volume of this work np to date, I have to express my thanks to Mr. T. H. Dnrrans, M.Sc., F.I.C., of Messrs. Boake, Boherts Co. s Research Laboratories for contributing the chapter on the Relationship of Odonr to Chemical Constitution, a subject to which Mr. Durrans has devoted considerable attention. I have also to thank Mr. Maurice Salamon, B.Sc., and Mr. C. T. Bennett, B.Sc., F.I.C., for reading and revising the chapter on the Analysis of Essential Oils. 

Masada. Y. Analysis of Essential Oils by GC and MS. New York John Wiley. 1976. 

Marriott PJ, Shellie R, Cornwell C, Gas chromatographic technologies for the analysis of essential oils, / Chromatogr A 936 1—22, 2001. 

Shellie R, Marriott P, Cornwell C, Application of comprehensive two-dimensional gas chromatography (GC GC) to the enantioselective analysis of essential oils, J Sep Sci 24 823-830, 2001. 

Another technique is NMR, which can be successfully utilised in the direct analysis of essential oils without need to separate them by GC [5, 78]. 

Several manufacturers of gas chromatographs now offer all glass splitters for use with glass capillary columns. Figure 6.13 is one design available. Splitters are generally used for solventless samples and also in petroleum and petro-chemistry a and for the analysis of essential oils. 

Analysis of essential oils with a view to identifying them and of determining their value and purity is based on the measurement of certain physical characters, on the estimation of certain special components (esters, alcohols, aldehydes, etc.), and on tests for the various substances which are commonly used for purposes of adulteration. 

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