Differentiation of wood-derived vanillin from synthetic vanillin in distillates using gas chromatography/combustion/isotope ratio mass spectrometry for 13C analysis

RationaleTypical storage in oak barrels releases in distillates different degradation products such as vanillin, which play an important role in flavour and aroma. The addition of vanillin, as well as other aroma compounds, of different origin is prohibited by European laws. As vanillin samples from different sources have different C-13 values, the C-13 value could be used to determine whether the vanillin is authentic (lignin-derived), or if it has been added from another source (e.g. synthetic). MethodsThe C-13 values for vanillin derived from different sources, including natural, synthetic and tannins, were measured by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS), after diethyl ether addition and/or ethanol dilution. A method for analysing vanillin in distillates after dichloromethane extraction was developed. Tests were undertaken to prove the reliability, reproducibility and accuracy of the method with standards and samples. Distillate samples were run to measure the C-13 values of vanillin and to compare them with values for other sources of vanillin. Results(13)C values were determined for: natural vanillin extracts (-21.0 to -19.3, 16 samples); vanillin ex-lignin (-28.2 parts per thousand, 1 sample); and synthetic vanillin (-32.6 to -29.3 parts per thousand, 7 samples). Seventeen tannin samples were found to have C-13 values of -29.5 to -26.7 parts per thousand, which were significantly different (p < 0.05) from those of the natural and synthetic vanillins. The vanillin C-13 values measured in distillates (-28.9 to -25.7 parts per thousand) were mainly in the tannin range, although one spirit (-32.5 parts per thousand) was found to contain synthetic vanillin. ConclusionsThe results show that synthetic vanillin added to a distillate could be differentiated from vanillin derived from oak barrels by their respective C-13 values. The GC/C/IRMS method could be a useful tool in the determination of adulteration of distillates.