Validation of gas chromatographic methods for lavender essential oil authentication based on volatile organic compounds and stable isotope ratios

Abstract

A combination of Gas Chromatography-tandem Mass Spectrometry (GC-MS/MS) and Gas Chromatography-Isotope Ratio Mass Spectrometry (GC-IRMS) methods is a powerful tool to control false declaration of various food matrices including lavender essential oil. However, the methods need to be validated to demonstrate data reliability.In the present study, we developed a GC-MS/MS method for determining volatile organic compounds in lavender essential oil. For this, a single chromatographic run was optimised to separate thirty-eight pure reference standards in<17 min using a suitable capillary column, a faster injection system, temperature ramp gradient, and acquiring mass spectra through dynamic monitoring reaction and full scan mode. The GC-MS/MS method was validated according to the “Harmonised guidelines of IUPAC” considering parameters such as linearity range, limit of detection, limit of quantification, regression coefficient, repeatability and reproducibility. The validation parameters suggested that the method was sufficiently sensitive, precise and accurate for the determination of VOCs.Moreover, we developed a GC-IRMS method to characterize the isotope ratios of carbon (δ13C) and hydrogen (δ2H) of a large selection of the VOCs present in the lavender oil. For this, different matrices of various essential oil compounds of known δ13C and δ2H values (obtained from bulk isotope ratio analysis) were analysed in the GC-IRMS. Similarly to the GC-MS/MS method, the GC-IRMS method was validated according to the recommendation by the Forensic Isotope Ratio Mass Spectrometry Network (FIRMS). In particular, the linearity test suggested that concentrations of at least 25 mg L−1 and 200 mg L−1 were required to produce reliable δ13C and δ2H values, respectively. Both δ13C and δ2H values were satisfactorily repeatable, reproducible and accurate. As expected, precision and accuracy of the δ2H were lower than those of the δ13C.Finally, the practical applicability of the methods was confirmed by the analysis of 3 lavender and 3 lavandin essential oil samples. We quantified the concentrations of 71 VOCs and the δ13C value of 32 and δ2H value of 30 compounds in real essential oil samples. These preliminary results showed that the combination of GC-MS/MS and GC-IRMS is potentially useful for botanical classification between lavender and lavandin essential oils thus representing an additional powerful tool for assessing the authenticity of commercial essential oils.