Laser-based measurements of ¹⁸O/¹⁶O stable isotope ratios (δ¹⁸O) in wine samples

Manish Gupta,¹ J Brian Leen,¹ Elena Simone Franklin Berman,¹ Aldo Ciambotti<sup>2

1</sup>Los Gatos Research, Mountain View, CA, USA; ²Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Centro di Ricerca per l'Enologia, Asti, Italy

Abstract: Wine counterfeiting is an international, multi-billion dollar issue, with some estimates suggesting that up to 5% of wines sold at auctions or secondary markets are fraudulent. Isotope ratio mass spectrometer (IRMS) measurements of the ¹⁸O/¹⁶O stable isotope ratio (δ¹⁸O) of water-in-wine have been used for wine authentication; however, these analyses are time-consuming and costly. In this preliminary study, off-axis integrated cavity output spectroscopy (OA-ICOS) is used to quantify δ¹⁸O in wines. This laser-based method has been extensively used to study water isotopes for hydrological and medical applications. Recently, the development of a spectral contaminant identifier (SCI) has extended the application of these OA-ICOS analyzers to contaminated water samples (eg, plant, soil, and leaf waters). Here, we utilize OA-ICOS with the SCI to characterize wine samples (9%–15% ethanol), and show that the laser-based instrument provides a δ¹⁸O measurement precision of ±0.07‰ (1σ) and agrees with IRMS to within ±0.63‰ (1σ). Moreover, by training the SCI on isotopically-characterized wines, the agreement with IRMS improves to within ±0.30‰ (1σ). The utility of the instrument is demonstrated by measuring watered and mixed wines. The method presented here can be readily extended to address other food authentication applications.

Keywords: wine isotopes, wine fraud, counterfeit wines, OA-ICOS