Chapter 15: Study of the Chemical Composition of Essential Oils by Gas Chromatography.

ESTER R. CHAMORRO, SILVIA N. ZAMBÓN, WALTER G. MORALES, ALFREDO F. SEQUEIRA AND GUSTAVO A. VELASCO.

Gas Chromatography in Plant Science, Wine Technology, Toxicology and Some Specific Applications.

INTECH

Año: 2012; p. 307 - 324

P { margin-bottom: 0.21cm; } Essential oils are complex mixtures, constituted by terpenoid hydrocarbons, oxygenated terpenes and sesquiterpenes. They originate from the plant secondary metabolism and are responsible for their characteristic aroma. The various applications of essential oils account for the great interest in their study. Such applications may be found in the cosmetic industry, as ingredients of fragrances, decorative cosmetic, fine fragrances and flavouring, in the food industry, as aromas and flavours, in the pharmaceutical industry, as active components of medicines and as antibacterials/antimicrobials, and in aromatherapy. At present, there are many studies in which they are used as intermediaries in fine chemistry reactions, among other applications. The most common methods used for the industrial extraction of these oils are steam-distillation, extraction with solvents and expression. Their selection will depend on the characteristics of the material from which the oil will be extracted, since they can be presentin different parts of the plant, like the roots, the stem, the leaves, the fruits and/or the seeds. Once the oils are obtained, the fundamental contribution of the organic chemistry to the industry resides in their characterisation, as their chemical composition may vary even whithin one botanical species. These variations might be due to the presence of different chemotypes, according to the plant adaptation to the surrounding environment, as well as its state of development. We have to take into account the fact that it is the composition of the essential oils what provides their intrinsic properties and economic value. The development of chromatographic techniques has allowed us to make considerable progress in the study of the chemical composition of essential oil. Gas Chromatography (GC) is, by all means, the best method, due to its simplicity, rapidity and efficiency, for both the identification and quantification of essential oil components and composition variations. The aim of this chapter is to describe the different applications of GC, starting from the quality control up to the identification and quantification of the chemical components of essential oils from different aromatic species that grow in the northeast of Argentina, which have emerged as a result of years of experience in this topic. In regards to the applications of GC, different studies will be presented, among which we will discuss the optimization of the operational conditions used to separate the different components, the analysis of the variation in the composition of regional essential oils, the measurement, using internal standards, of oils as well as oil modification by fractional vacuum distillation, and the study of semi-synthesis reactions to obtain high added-value compounds, starting from oils or their components.