Deuterium/hydrogen ratio analysis of thymol, carvacrol, gamma-terpinene and p-cymene in thyme, savory and oregano essential oils by gas chromatography-pyrolysis-isotope ratio mass spectrometry

摘要

Isotope ratio mass spectrometry online coupled with capillary gas chromatography (GC-Py-IRMS) on column INNOWAX is used in the origin specific analysis and the authenticity control of the phenolic essential oils (EOs). Isotopic data delta H-2(V-SMOW) of thymol and carvacrol in natural essential oils were evidently more depleted than synthetic products (from -49 to 7 parts per thousand for thymol and -61 parts per thousand for carvacrol). 32 HV-SMOW values of p-cymene, gamma-terpinene and thymol in authentic thyme oils (Thymus vulgaris L. and Thymus zygis L.) were found from -300 to -270 parts per thousand, from -285 to -248 parts per thousand and from -259 to -234 parts per thousand, respectively. 82 HV-SMOW values of carvacrol and p-cymene in authentic oregano oils (Origanum heracleoticum L., Coridothymus capitatus L. and Origanum compactum L.) varied from -223 to - 193 parts per thousand and from -284 to -259 parts per thousand, respectively. For authentic Satureja montana subsp. montana essential oils, the mean delta H-2(V-SMOW) value for aromatic compounds were found to be the following: gamma-terpinene -273 parts per thousand (SD = 4.6 parts per thousand) and p-cymene -283 parts per thousand (SD = 3.0 parts per thousand), thymol -245 parts per thousand (SD = 1.8 parts per thousand) and carvacrol -226 parts per thousand (SD = 1.7 parts per thousand). In addition, p-cymene was previously found as a precursor of the biosynthesis of thymol and carvacrol in thyme oil, thus, we considered p-cymene as an endogenous reference compound (ERC) for D/H ratio analysis. The isotopic fractionation factors at alpha(thymol/p-cymene) = 1.05 and alpha(carvacrol/p-cymene) = 1.08 were obtained and also used to control the authenticity of the phenolic EOs. (c) 2006 Elsevier B.V. All rights reserved.