O-18 Internal Referencing Method to Detect Water Addition in Wines and Fruit Juices: Interlaboratory Study

An interlaboratory study of the oxygen 18-isotope ratio MS (O-18-IRMS) method using water and ethanol for detecting water addition in wines and fruit juices is reported. The measurement of these two parameters constitutes an internal referencing approach contributing to a better detection of a certain kind of adulteration of wines and fruit juices. In this approach, the same initial steps as in the AOAC Official Methods 995.17 and 2004.01 are used to recover pure ethanol: Fruit juices are completely fermented using yeast, and the alcohol is distilled from the fermented juice or from the wine with a quantitative yield (>96%). Then the O-18 deviation (delta O-18) of ethanol is determined by IRMS. This parameter is compared with the delta O-18 of water determined by the so-called equilibration procedure using CO2 gas. An interlaboratory study was organized by our laboratory in 2011 to establish performance data for determinations in wines and fruit juices. The study was organized and interpreted according to the guidelines of the International Union of Pure and Applied Chemistry International Harmonized protocol. Thirteen laboratories analyzed five juice materials (two orange, one pineapple, one grape, and one apple) and five wine materials (three red, one white, and one rose) as blind duplicates. The pooled among-laboratories reproducibility of the method for measuring delta O-18 in water was found to be 0.8 parts per thousand for both wines and fruit juices. The pooled among-laboratories reproducibility of the method for measuring delta O-18 in ethanol was found to be in the order of 1.0 parts per thousand for wine and orange juice, and around 2.2 parts per thousand for the other fruit juice types tested.