Precision, accuracy and referencing of isotope ratios determined by nuclear magnetic resonance

Summary The precision and accuracy of site-specific and average hydrogen isotope ratios determined by NMR are checked according to the ISO norms. The consistency of the results is investigated by comparison with the values of the mean isotope ratios measured by mass spectrometry. Several kinds of molecular species from different natural origins have been studied: water, ethanol, anethol, vanillin. A very good agreement between MS and NMR results is found for water. The limitations and advantages of NMR for the determination of average deuterium contents of organic molecules are discussed. A satisfactory precision of the NMR measurements can usually be reached, however systematic deviations of a few ppm between MS and NMR results may occur. By using either MS or NMR mean isotope ratios, site-specific parameters can be obtained by SNIF-NMR with an accuracy which is strongly dependent on the structure of the molecular species. The role and the importance of the reference materials in quantitative isotope determinations are stressed.

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Genauigkeit, Richtigkeit und Verifizierung von Isotopenverhältnissen mit Hilfe der NMR-Spektroskopie