Abstract
A new method, combining headspace solid phase microextraction (HS-SPME) with an online pyrolysis system coupled with isotope ratio mass spectrometry (IRMS), is developed for the determination of the intramolecular (13)C isotope composition of ethanol in aqueous solutions. The δ(13)C values of the pyrolytic fragments (CO, CH4, C2H4) are shown to be highly reproducible (sd <0.4‰). Furthermore, using 14 ethanol samples of known intramolecular isotope distribution, the CO and CH4 fragments are shown to arise solely from the methylene (CH2OH) and methyl (CH3) carbon atom positions of the original ethanol, respectively. Although the different steps (extraction and pyrolysis) fractionate between (12)C and (13)C, the isotopic fractionation is reproducible (sd <0.4‰), allowing correcting factors to be applied in order to back-calculate the original δ(13)CCH2OH and δ(13)CCH3 values of ethanol. The method thus allows the determination of the isotope composition of ethanol at the intramolecular and molecular levels, within a single run and a short experimental time (30 min), and with a very easy sample preparation. The method is then applied to alcoholic beverages to show its potential for authentication purposes.
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