Laser-based measurements of [sup.18]O/[sup.l6]O stable isotope ratios in wine samples

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 [sup.18]O/[sup.16]O stable isotope ratio (δ[sup.18]O) 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 δ[sup.18]O 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 S18O measurement precision of ± 0.07%o (1σ) and agrees with IRMS to within ± 0.63%o (1σ). Moreover, by training the SCI on isotopically-characterized wines, the agreement with IRMS improves to within ±0.30%o (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