Collection and identification of an unknown component from Eugenia uniflora essential oil exploiting a multidimensional preparative three-GC system employing apolar, mid-polar and ionic liquid stationary phases

Preparative three-dimensional GC and nuclear magnetic resonance for the isolation and identification of two sesquiterpene ethers from Dictyota Dichotoma

Separation science plays a crucial role in the isolation of novel compounds contained in complex matrices. Yet their rationale employment needs preliminary structure elucidation, which usually requires sufficient aliquots of grade substances to characterize the molecule by nuclear magnetic resonance experiments. In this study, two peculiar oxa-tricycloundecane ethers were isolated by means of preparative multidimensional gas chromatography from the brown alga species Dictyota dichotoma (Huds.) Lam., aiming to assign their 3D structures. Density functional theory simulations were carried out to select the correct configurational species matching the experimental NMR data (in terms of enantiomeric couples). In this case, the theoretical approach was crucial as the protonic signal overlap and spectral overcrowding were preventing any other unambiguous structural information. Just after the identification through the density functional theory data matching of the correct relative configuration it was possible to verify an enhanced self-consistency with the experimental data, confirming the stereochemistry. The results obtained further pave the way toward structure elucidation of highly asymmetric molecules, whose configuration cannot be inferred by other means or strategies.

Expanding the Knowledge Related to Flavors and Fragrances by Means of Three-Dimensional Preparative Gas Chromatography and Molecular Spectroscopy

As universally known, gas chromatography (GC) coupled with mass spectrometry (MS) allows us to acquire spectra that can be searched in specific databases to attain qualitative information on a peak of interest. When not present in databases, structure elucidation is required before including a new component in a library: from that moment, scientists all around the world will be able to identify the new molecule with analytical confidence after GC-MS analysis. Conversely, if data are not shared in commercial databases, even if a molecule is studied and elucidated, it appears to be unknown or only identifiable on the basis of third-party data taken from the literature, which is a serious limitation. The present paper deals with a case that confirms this assumption. A component of Myrtus communis L. volatile fraction was tentatively identified based on literature data. Despite this, reliable identification could not be achieved due to the lack of a corresponding spectrum in commercial MS databases. Afterwards, the target component was isolated in a reasonable quantity and with a high degree of purity for downstream characterization by spectroscopic techniques. For this purpose, preparative (prep) GC may appear insufficient for the isolation of volatile components from highly complex samples. In this study, a prep-MDGC system was implemented for the isolation of the compound of interest from myrtle oil, consisting of three wide-bore columns of different selectivity coupled by means of Deans switch transfer devices. Based on the NMR and GC-FTIR data acquired, the unknown compound was identified as 2,2,5,5,7,7-hexamethyl-3,7-dihydro-1-benzofuran-4,6(2H,5H)-dione. Noticeably, this is a known molecule, yet its mass spectrum had never been registered into MS databases and thus was not available to the scientific community. Finally, the spectrum was included for the first time in a commercial library, namely the FFNSC 5.0 MS database. The aim of the present study was to highlight the opportunity to make analytical data quickly available in a reliable way by registering them in searchable MS databases to improve the identification means for researchers all over the world.

Relationships in Gas Chromatography—Fourier Transform Infrared Spectroscopy—Comprehensive and Multilinear Analysis

Molecular spectroscopic detection techniques, such as Fourier transform infrared spectroscopy (FTIR), provides additional specificity for isomers where often mass spectrometry (MS) fails, due to similar fragmentation patterns. A hyphenated system of gas chromatography (GC) with FTIR via a light-pipe interface is reported in this study to explore a number of GC–FTIR analytical capabilities. Various compound classes were analyzed—aromatics, essential oils and oximes. Variation in chromatographic peak parameters due to the light-pipe was observed via sequentially-located flame ionization detection data. Unique FTIR spectra were observed for separated mixtures of essential oil isomers having similar mass spectra. Presentation of GC×FTIR allows a ‘comprehensive’-style experiment to be developed. This was used to obtain spectroscopic/separation profiles for interconverting oxime species with their individual spectra in the overlap region being displayed on a color contour plot. Partial least square regression provides multivariate quantitative analysis of co-eluting cresol isomers derived from GC–FTIR data. The model resulted in an R2 of 0.99. Prediction was obtained with R2 prediction value of 0.88 and RMSEP of 0.57, confirming the method’s suitability. This study explores the potential of GC–FTIR hyphenation and re-iterates its value to derive unambiguous and detailed molecular information which is complementary to MS.