Intrinsic ratios of glucose, fructose, glycerol and ethanol ¹³C/¹²C isotopic ratio determined by HPLC-co-IRMS: toward determining constants for wine authentication

Abstract

High-performance liquid chromatography linked to isotope ratio mass spectrometry (HPLC-co-IRMS) via a Liquiface© interface has been used to simultaneously determine ¹³C isotope ratios of glucose (G), fructose (F), glycerol (Gly) and ethanol (Eth) in sweet and semi-sweet wines. The data has been used the study of wine authenticity. For this purpose, 20 authentic wines from various French production areas and various vintages have been analyzed after dilution in pure water from 20 to 200 times according to sugar content. If the ¹³C isotope ratios vary according to the production area and the vintage, it appears that internal ratios of ¹³C isotope ratios $\left( {R_{^{13} C} } \right)$ of the four compounds studied can be considered as a constant. Thus, ratios of isotope ratios are found to be 1.00 ± 0.04 and 1.02 ± 0.08 for $R_{^{13} C_{G/F} }$ and $R_{^{13} C_{Gly/Eth} }$, respectively. Moreover, $R_{^{13} C_{Eth/Sugar} }$ is found to be 1.15 ± 0.10 and 1.16 ± 0.08 for $R_{^{13} C_{Gly/Sugar} }$. Additions of glucose, fructose and glycerol to a reference wine show a variation of the $R_{^{13} C}$ value for a single product addition as low as 2.5 g/L⁻¹. Eighteen commercial wines and 17 concentrated musts have been analyzed. Three wine samples are suspicious as the $R_{^{13} C}$ values are out of range indicating a sweetening treatment. Moreover, concentrated must analysis shows that ¹³C isotope ratio can be also used directly to determine the authenticity of the matrix.