title: Conditions to obtain precise and true measurements of the intramolecular 13C distribution in organic molecules by isotopic 13C nuclear magnetic resonance spectrometry.
abstract: Intramolecular (13)C composition gives access to new information on the (bio) synthetic history of a given molecule. Isotopic (13)C NMR spectrometry provides a general tool for measuring the position-specific (13)C content. As an emerging technique, some aspects of its performance are not yet fully delineated. This paper reports on (i) the conditions required to obtain satisfactory trueness and precision for the determination of the internal (13)C distribution, and (ii) an approach to determining the "absolute" position-specific (13)C content. In relation to (i), a precision of <1% can be obtained whatever the molecule on any spectrometer, once quantitative conditions are met, in particular appropriate proton decoupling efficiency. This performance is a prerequisite to the measurement of isotope fractionation either on the transformed or residual compound when a chemical reaction or process is being studied. The study of the trueness has revealed that the response of the spectrometer depends on the (13)C frequency range of the studied molecule, i.e. the chemical shift range. The "absolute value" and, therefore, the trueness of the (13)C NMR measurements has been assessed on acetic acid and by comparison to the results obtained on the fragments from COOH and CH3 by isotopic mass spectrometry coupled to a pyrolysis device (GC-Py-irm-MS), this technique being the reference method for acetic acid. Of the two NMR spectrometers used in this work, one gave values that corresponded to those obtained by GC-Py-irm-MS (thus, the "true" value) while the other showed a bias, which was dependent to the range covered by the resonance frequencies of the molecule. Therefore, the former can be used directly for studying isotope affiliations, while the latter can only be used directly for comparative data, for example in authenticity studies, but can also be used to obtain the true values by applying appropriate correction factors. The present study assesses several key protocol steps required to enable the determination of position-specific (13)C content by isotopic (13)C NMR, irrespective of the NMR spectrometer: parameters to be adjusted, performance test using [1,2-(13)C2]acetic acid, generation of correction factors.
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France.
authors.forename: Kevin
authors.initials: K
authors.lastname: Bayle
authors.affiliation: Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan; Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
authors.forename: Alexis
authors.initials: A
authors.lastname: Gilbert
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France.
authors.forename: Maxime
authors.initials: M
authors.lastname: Julien
authors.affiliation: Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Yamada
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France.
authors.forename: Virginie
authors.initials: V
authors.lastname: Silvestre
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Robins
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France.
authors.forename: Serge
authors.initials: S
authors.lastname: Akoka
authors.affiliation: Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8503, Japan; Earth-Life Science Institute, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yoshida
authors.affiliation: EBSI Team, Interdisciplinary Chemistry: Synthesis, Analysis, Modelling (CEISAM), University of Nantes-CNRS UMR 6230, 2 Rue de la Houssinière, BP 92208, F-44322, Nantes Cedex 3, France. Electronic address: gerald.remaud@univ-nantes.fr.
authors.forename: Gérald S
authors.initials: GS
authors.lastname: Remaud
mesh_terms: D019342:Acetic Acid / Q000032:analysis; D002138:Calibration; D002247:Carbon Isotopes / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*
chemical_list: D002247:Carbon Isotopes; D019342:Acetic Acid
keywords: Intramolecular isotopic composition; Isotopic (13)C NMR spectrometry; NMR spectrometer qualification; Quantitative NMR; Trueness and precision