Isotopic ratio mass spectrometry: from bulk analysis to the coupling with enantio-multidimensional gas chromatography for the authenticity assessment of premium products

The PhD activity aimed to the evaluation of the applicability of isotopic ratio mass spectrometry for the authenticity assessment of premium products, from the analysis of whole samples by means of bulk stable isotope analysis to the development of advanced chromatographic approaches. Starting from bulk analysis, a thorough investigation of Cannabis Sativa L. products was carried out, by analysing the main stable isotopes, namely 13C/12C, 18O/16O, 2D/1H, 15N/14N, 34S/32S. (Chapter 2). This research allowed determining the characteristic isotopic distribution of different hemp parts, such as inflorescences, seeds and roots, representing a reliable authenticity range for genuine samples. However, despite the renowned capability of bulk analysis to evaluate the isotopic distribution of a matrix, adulteration may sometimes involve only target components, thus requiring advanced analytical devices prior to IRMS detection. In this concern, gas chromatography is by far the preferred analytical method to evaluate the isotopic ratio of key separated volatile components. Nevertheless, the coupling of gas chromatography to isotopic ratio mass spectrometry (GC-C-IRMS) requires the condition of baseline resolution for the reliable detection of the isotopic ratios. Due to the uneven distribution of 13C and 12C isotopes along an entire peak of CO2, co-elutions represent a critical matter and deny the achievement of reliable data. In this concern, a deep investigation was carried out to evaluate the applicability of monodimensional GC-C-IRMS in the analysis of complex samples, demonstrating the need for multidimensional gas chromatography to achieve reliable isotopic results (Chapter 5). As well as isotopic ratio mass spectrometry, enantio-selective gas chromatography covers a key role in the field of authenticity assessment. The production of typical enantiomeric excesses for target volatiles is directly related to the biosynthetic pathways of the plant of origin, representing a valuable tool to discriminate between genuine and adulterated samples. Due to the capability of both techniques to investigate in depth the biochemical steps of the sample investigated, the main aim was to hyphen the enantio-selective GC separation to the IRMS detection. As well as for the monodimensional GC-C-IRMS application reported in Chapter 5, even in this case several issues were involved by applying a monodimensional enantio-selective GC-C-IRMS approach. To these aims, enantio-selective multidimensional gas chromatographic methods, with a simultaneous single quadrupole and IRMS detection, were developed for the analysis of different valuable products, such as Cannabis Sativa L. essential oils (Chapter 7), volatile organic components of Moscato Giallo grapes (Chapter 8) and lemon essential oils (Chapter 9). This system allowed evaluating simultaneously the enantiomeric and isotopic ratios of key components, clearly reducing total time analysis. Moreover, this coupling allows determining the specific isotopic ratio of each enantiomer separated. Whilst most of the literature references described how no isotopic differences should be expected between the enantiomers of the same couple, different isotopic signatures were registered for the dextro and levorotatory enantiomers of α and β-pinene in the case of lemon essential oils (Chapter 9). This finding paves the way for newer considerations in the field of authenticity assessment since different essential oil types may present typical chiral isotopic fractionation processes.