Site-specific (13) С/(12) С isotope abundance ratios in dicarboxylic oxyacids as characteristics of their origin.

Rationale: Recommendations of relevant international organizations controlling the quality of grape wines and beverages specify that only tartaric acids of grape origin can be introduced to achieve the required parameters. The development of methods for determining the origin of tartaric acid in grape wine is of great technological significance.

Methods: Organic dicarboxylic oxyacids were extracted from wines as barium salts. Carbon dioxide, which included all the carbon atoms of the acids, was used to determine the carbon isotope ratios by Isotope Ratio Mass Spectrometry. The alkyl part of the oxyacids was burned at 560°C in the presence of air; BaCO3 containing the carboxyl carbon was left. This carbonate was used to measure the carbon isotope ratios in the carboxyl part of the acid. The carbon isotope ratios of the alkyl part of tartaric acid were found by isotope mass balance.

Results: The carbon isotope composition of carboxyl groups (δ(13) С values) in tartaric acid of grape (biogenic origin) had a higher (13) С content than the carbon in the alkyl part of the molecule. Tartaric acid produced by chemical synthesis (abiogenic origin) was noted to have a different (13) С/(12) С distribution: the carboxyl group of tartaric acid produced by chemical synthesis contained a smaller than or equal amount of (13) С to the alkyl part.

Conclusions: This is the first determination of the site-specific distribution of the (13) С/(12) С isotopes in tartaric acids as evidence of their biogenic and abiogenic origins. The presented method for determining the origin of tartaric acid can be used for efficient control of the quality of grape wines and beverages.