Measurement of δ¹⁸O and δ²H of water and ethanol in wine by Off-Axis Integrated Cavity Output Spectroscopy and Isotope Ratio Mass Spectrometry

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.