Determination of the 13C/12C ratios of ethanol and higher alcohols in wine by GC-C-IRMS analysis

More than 50 authentic EU data bank wines from Germany (vintages: 2003, 2004 and 2006) have been extracted by liquid-liquid extraction with a mixture of cyclohexane and 2-methyl-2-propanol. The delta C-13 values of the extracted wine ethanol and other co-extracted higher alcohols have been determined by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). The stable isotope ratios of wine ethanol obtained by liquid-liquid extraction were compared with those obtained after distillation according to the official EU method. No significant differences of the isotope ratios of ethanol measured by the two compared methods were found (R (2) = 0.972), thus it was concluded that no significant isotope effect during sample preparation occurred. Additionally, the C-13/C-12 isotope ratios of the major co-extracted alcohols, e.g. 2-methylpropan-1-ol, 2- and 3-methylbutan-1-ol, butan-2,3-diol and 2-phenyl-1-ethanol were determined and set in relation to the delta C-13 values of the corresponding extracted wine ethanol. Also, high correlations between their isotope ratios (e.g. 2,3-methylbutan-1-ol R (2) = 0.829) were found. The key benefits of the introduced liquid-liquid extraction are the time- and cost-saving determination of delta C-13 values of wine ethanol, the small amount of sample needed for the extraction and additionally the potential analysis of the co-extracted higher alcohols which could be valuable for the detection of fraud.