Site-specific 13C content by quantitative isotopic 13C Nuclear Magnetic Resonance spectrometry: A pilot inter-laboratory study

Isotopic 13C NMR spectrometry, which is able to measure intra-molecular 13C composition, is of emerging demand, because of the new very insteresting information brought by 13C site-specific content of a given molecule. A systematic evaluation of instrumental behavior is of importance to envisage isotopic 13C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular 13C composition by NMR. The main goals of the ring test were to establish an intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise based on a qualification test. Then the reproducibility at natural abundance of isotopic 13C NMR was assessed on vanillin from three different origins associated to specific δ 13Ci profiles. The standard deviation was, in average, between 0.9 and 1.2‰ for the intra-variability. The highest standard deviation for the inter-variability was 2.1‰. This is significantly higher than the internal precision but it could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ 13Ci in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument is very satisfactory, correcting factors for each carbon in vanillin could be calculated to harmonize the results. Isotopic 13C NMR spectrometry, which is able to measure intra-molecular 13C composition, is of emerging demand, because of the new very insteresting information brought by 13C site-specific content of a given molecule. A systematic evaluation of instrumental behavior is of importance to envisage isotopic 13C NMR as a routine tool. This paper describes the first collaborative study of intra-molecular 13C composition by NMR. The main goals of the ring test were to establish an intra- and inter-variability of the spectrometer response. Eight instruments with different configuration were retained for the exercise based on a qualification test. Then the reproducibility at natural abundance of isotopic 13C NMR was assessed on vanillin from three different origins associated to specific δ 13Ci profiles. The standard deviation was, in average, between 0.9 and 1.2‰ for the intra-variability. The highest standard deviation for the inter-variability was 2.1‰. This is significantly higher than the internal precision but it could be considered good in respect of a first ring test on a new analytical method. The standard deviation of δ 13Ci in vanillin was not homogeneous over the eight carbons, with no trend either for the carbon position or for the configuration of the spectrometer. However, since the repeatability for each instrument is very satisfactory, correcting factors for each carbon in vanillin could be calculated to harmonize the results.JRC.I.1-Chemical Assessment and Testin