A new procedure for the determination of carbon dioxide (CO 2 ) 13 C/ 12 C isotope ratios, using direct injection into a GasBench/isotope ratio mass spectrometry (GasBench/IRMS) system, has been developed to improve isotopic methods devoted to the study of the authenticity of sparkling drinks. Thirty-nine commercial sparkling drink samples from various origins were analyzed. Values of d 13 C cava ranged from S20.30% to S23.63%, when C3 sugar addition was performed for a second alcoholic fermentation. Values of d 13 C water ranged from S5.59% to S6.87% in the case of naturally carbonated water or water fortified with gas from the spring, and d 13 C water ranged from S29.36% to S42.09% when industrial CO 2 was added. It has been demonstrated that the addition of C4 sugar to semi-sparkling wine (aguja) and industrial CO 2 addition to sparkling wine (cava) or water can be detected. The new procedure has advantages over existing methods in terms of analysis time and sample treatment. In addition, it is the first isotopic method developed that allows Carbon dioxide (CO 2 ) is used to give drinks a slightly acidic and more pleasant taste. 1 CO 2 gas bubbles, either naturally present or added, characterize several beverage products: water, wine, beer, soft drinks, etc. Nowadays, some aspects of CO 2 in beverages, such as purity and concentration, are regulated by European Union (EU) legislation. 2 The CO 2 responsible for effervescence in sparkling wines, which includes French Champagne, Italian Spumante and Spanish Cava, is produced in closed bottles during the second alcoholic fermentation or 'prise de mousse'. CO 2 is produced together with ethanol when yeast ferment sugars.In the last 20 years, stable isotope ratio measurements have been used to prevent fraud in the food products industry. 3 These methods are based on the measurements of the stable isotope ratios of the biologically important elements, 2 H/ 1 H, 13 C/ 12 C, 15 N/ 14 N, and 18 O/ 16 O, by isotope ratio mass spectrometry (IRMS).Carbon stable isotope methods are based on the fact that a molecule (e.g. sugars) exhibits varying 13 C isotope concentrations depending on the plant which has metabolized it and therefore its stable isotope ratio can provide information on its botanical origin. In C3 plants (Calvin cycle) 3-ribulose diphosphate is used to fix the CO 2 , and the 13 C/ 12 C abundance ratios, expressed as the d 13 C values, lie in the À23 to À28% range. 4 C4 plants (dicarboxylic acid route or Hatch-Slack pathway) use oxaloacetate as the CO 2 acceptor and have d 13 C values between À9 and À15%. 5 For several fermented products, CO 2 reflects the botanical origin of the sugars from which the gas originates. 6 Cane sugar is a C4 plant while the grapevine is a C3 plant. It is thus possible to distinguish by IRMS between the CO 2 produced from the fermentation of the sugar present in the grape must and that originating from added cane sugar. 7 Industrial CO 2 used in the food industry has a large range of d 13 C values (1 to À75%), depending on the pr...