Abstract
There are two officially approved methods for stable isotope analysis for wine authentication. One describes δ18O measurements of the wine water using Isotope Ratio Mass Spectrometry (IRMS), and the other one uses Deuterium-Nuclear Magnetic Resonance (2H-NMR) to measure the deuterium of the wine ethanol. Recently, off-axis integrated cavity output (laser) spectroscopy (OA-ICOS) has become an easier alternative to quantify wine water isotopes, thanks to the spectral contaminant identifier (SCI). We utilized an OA-ICOS analyser with SCI to measure the δ18O and δ2H of water in 27 wine samples without any pre-treatment. The OA-ICOS results reveal a wealth of information about the growth conditions of the wines, which shows the advantages to extend the official δ18O wine water method by δ2H that is obtained easily from OA-ICOS. We also performed high-temperature pyrolysis and chromium reduction combined with IRMS measurements to illustrate the “whole wine” isotope ratios. The δ18O results of OA-ICOS and IRMS show non-significant differences, but the δ2H results of both methods differ much more. As the δ2H difference between these two methods is mainly caused by ethanol, we investigated the possibility to deduce deuterium of wine ethanol from this difference. The results present large uncertainties and deviate from the obtained 2H-NMR results. The deviation is caused by the other constituents in the wine, and the uncertainty is due to the limited precision of the SCI-based correction, which need to improve to obtain the 2H values of ethanol as alternative for the 2H-NMR method.
Highlights
Wine authenticity control is vital to protect consumers and for the proper functioning of the world market with regard to the increasing and globalized wine consumption
It is worth taking note that the δ2H measurements of the wine water are not officially used, the combination of δ2H and δ18O is more powerful in both fraud detection and characterisation of authentic wines
In an attempt to remove the various constituents of the wine, a fraction of each wine sample was treated with activated charcoal, to study if such removal would influence the Isotope Ratio Mass Spectrometry (IRMS) and OA-ICOS measurements
Summary
Wine authenticity control is vital to protect consumers and for the proper functioning of the world market with regard to the increasing and globalized wine consumption. To our knowledge, there are only two officially approved methods that use the 2H and 18O isotopes: the 18O relative abundance measurements (usually expressed as δ18O, see below) of the wine water using Isotope Ratio Mass Spectrometry (IRMS) (OIV-MA-AS2-12) and (sitespecific) 2H relative abundance measurements (usually expressed as the mole ratio of 2H to 1H) of the wine ethanol using Deuterium-Nuclear Magnetic Resonance (2H-NMR). It is worth taking note that the δ2H measurements of the wine water are not officially used, the combination of δ2H and δ18O is more powerful in both fraud detection and characterisation of authentic wines. It must be a heritage of the past when the δ2H measurements of water were difficult and costly. With the development of infrared optical spectroscopy measurement systems for isotope ratios, δ2H of the wine water is as accessible as δ18O
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