Application of co-distillation with superheated pentane vapour to the isolation of unstable essential oils

Hydrodistillation is the main method for essential oil isolation from aromatic plants. For unstable essential oils, this method is not suitable. For these cases, we have developed a method of isolation by co-distillation with superheated pentane vapour. The method was studied using plant materials of Mentha citrata and Salvia sclarea, which contain unstable linalyl acetate as the main component of their essential oils. The essential oils of the same plants were also isolated by hydrodistillation as a standard method. The isolated volatiles (with both methods) were analysed by gas chromatography-mass spectrometry (GC-MS) and the obtained results were compared. Significant differences were found in the qualitative and quantitative composition of isolated volatiles. The major components of the volatiles obtained by hydrodistillation and by co-distillation with superheated pentane vapour, respectively, were linalyl acetate (26.5%, 55.5%), linalool (29.3%, 15.8%), 1,8-cineole (7.2%, 3.5%), hedycaryol (6.2%, 6.6%) alpha-terpineol (5.5%, 0.7%) and geranyl acetate (4.9%, 2.9%) for Mentha citrata; and linalyl acetate (21.2%, 33.4%), linalool (16.6%, 6.0%), myrcene (8.4%, 10.2%), geranyl acetate (7.3%, 6.7%) alpha-terpineol (7.6%, 0.0%), trans-beta-ocimene (4.4%, 6.4%) and geraniol (3.8%, 0%) for Salvia sclarea. The method of co-distillation enables safe isolation of monoterpenes, but also sesquiterpene compounds as well as hydrodistillation. It is clear that this new method, unlike hydrodistillation, safely and remarkably diminishes artefact generation. Copyright (C) 2003 John Wiley Sons, Ltd.