Characterization of glycerol from different origins by 2H- and 13C-NMR studies of site-specific natural isotope fractionation

The site-specific natural isotope fractionation of carbon and hydrogen has been investigated by SNIF-NMR for glycerol samples, extracted from plant lipids, obtained in the fermentation of sugars, or from commercial sources. In the first two cases, several plant species from either C-3 or C-4 metabolic origin have been considered. Large deviations with respect to a statistical distribution of deuterium in the glycerol skeleton are observed and the dispersion ranges of the isotopic parameters are much larger than the precision of the measure. The NMR determination of the site-specific carbon isotopic parameters (positions 2 and 1,3 of glycerol) provides an easy method for distinguishing natural and synthetic samples. More generally, the discriminating potential of the carbon and hydrogen isotopic fingerprint of glycerol has been estimated on a statistical basis in terms of the nature of the raw material (plant oil or sugar fermentation) and, in each case, in terms of C-3 or C-4 metabolism of the precursor. Glycerol may be proposed as an isotopic probe for discriminating between olive and sunflower and for investigating the adulteration of wines.