| Résumé | Site-specific carbon isotope ratio measurements by quantitative ¹³C NMR (¹³C-qNMR), Orbitrap-MS, and GC-IRMS offer a new dimension to conventional bulk carbon isotope ratio measurements used in food provenance, forensics, and a number of other applications. While the site-specific measurements of carbon isotope ratios in vanillin by ¹³C-qNMR or Orbitrap-MS are powerful new tools in food analysis, there are a limited number of studies regarding the validity of these measurement results. Here we present carbon site-specific measurements of vanillin by GC-IRMS and ¹³C-qNMR for methoxy carbon. Carbon isotope delta (δ¹³C) values obtained by these different measurement approaches demonstrate remarkable agreement; in five vanillin samples whose bulk δ¹³C values ranged from −31‰ to −26‰, their δ¹³C values of the methoxy carbon ranged from −62.4‰ to −30.6‰, yet the difference between the results of the two analytical approaches was within ±0.6‰. While the GC-IRMS approach afforded up to 9-fold lower uncertainties and required 100-fold less sample compared to the ¹³C-qNMR, the ¹³C-qNMR is able to assign δ¹³C values to all carbon atoms in the molecule, not just the cleavable methoxy group. |
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