Chiral isotopic fractionation in lemon essential oil: A tool for authenticity assessment?

The present research aimed to retrieve key information about the genuineness of Sicilian lemon essential oils by evaluating simultaneously the chiral and isotopic data of target terpene components. With respect to previous literature references, where chiral recognition and isotope discrimination were performed by distinct gas chromatographic methods, this study aimed to develop a single analytical approach. To overcome limitations associated to monodimensional gas chromatographic approaches, an enantio‑selective multidimensional gas chromatographic approach coupled to isotopic ratio mass spectrometry and to parallel single quadrupole detection (Es-MDGC-C-IRMS/qMS) was developed. Thanks to the features of this system, enantiomeric excesses and target δ¹³C of the chiral and achiral components were evaluated in a single gas chromatographic run, allowing to reduce total time analysis, as well the consumption of electricity, solvents and samples. Moreover, due to the capability to baseline separate the enantiomeric couples, further considerations were done about the specific δ¹³C value of the target separated enantiomers. Dealing with the genuine lemon oils analysed, a different δ¹³C value was found between the enantiomers of the same chiral component, namely (-) and (+) of α and β-pinene, suggesting a different isotopic fractionation related to a specific biosynthetic pathway. This research aimed to evaluate the reasons behind this behaviour, paving the way to newer considerations in the field of authenticity assessment.