Comparison of Carbon Isotope Ratio Measurement of the Vanillin Methoxy Group by GC-IRMS and 13C-qNMR

Markus Greule; Phuong Mai Le; Juris Meija; Zoltán Mester; Frank Keppler

doi:10.1021/jasms.3c00327

Comparison of Carbon Isotope Ratio Measurement of the Vanillin Methoxy Group by GC-IRMS and ¹³C-qNMR

J Am Soc Mass Spectrom. 2024 Jan 3;35(1):100-105. doi: 10.1021/jasms.3c00327. Epub 2023 Nov 28.

Authors

Markus Greule¹, Phuong Mai Le², Juris Meija², Zoltán Mester², Frank Keppler¹

Affiliations

¹ Institute of Earth Sciences, Heidelberg University, Im Neuenheimer Feld 234-236, 69120 Heidelberg, Germany.
² Metrology, National Research Council Canada, 1200 Montreal Road, Ottawa, ON K1A 0R6, Canada.

Abstract

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.

Keywords: 13C-qNMR; GC-IRMS; Site-specific carbon isotope; vanillin methoxy group.