Infrared spectroscopy quantification of functional carbon groups in kerogens and coals: A calibration procedure

• Published in: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
• Main Authors: Phan, van T.H., Quirico, Eric, Beck, Pierre, Le Brech, Yann, Jovanovic, Lora, Le Guillou, Corentin, Bernard, Sylvain, Bonal, Lydie, Carrasco, Nathalie, Gautier, Thomas, Raya, Jesus
• Other Authors: Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Grenoble (OSUG )-Université Grenoble Alpes (UGA), Laboratoire Réactions et Génie des Procédés (LRGP), Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Unité Matériaux et Transformations - UMR 8207 (UMET), Centrale Lille-Institut de Chimie - CNRS Chimie (INC-CNRS)-Université de Lille-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Muséum national d'Histoire naturelle (MNHN)-Institut de recherche pour le développement IRD : UR206-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institut de Chimie de Strasbourg (IC), Université de Strasbourg (UNISTRA)-Institut de Chimie - CNRS Chimie (INC-CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Infrared spectroscopy; Nuclear magnetic resonance (NMR); Kerogens; Coals; Insoluble organic matter; Chondrites; Composition; [CHIM.ORGA]Chemical Sciences/Organic chemistry; Murchison; Tagish; Tagish Lake
• Online Access: https://insu.hal.science/insu-03208201; https://insu.hal.science/insu-03208201/document; https://insu.hal.science/insu-03208201/file/Phan-SpectrochimicaActa-2021-HAL.pdf; https://doi.org/10.1016/j.saa.2021.119853

International audience The determination of the abundances of the CH x , C=O and aromatic groups in chondritic Insoluble Organic Matter (IOM) and coals by Infrared (IR) spectroscopy is a challenging issue due to insufficient knowledge on the absorption cross-sections and their sensitivity to the molecular environment. Here, we report a calibration approach based on a 13 C synthetic model material whose composition was unambiguously determined by Direct-Pulse/Magic Angle Spinning Nuclear Magnetic Resonance (DP/MAS NMR). Ratios of the cross-sections of the CH x , C=O and aromatic groups have been determined, and the method has been applied to IOM samples extracted from four chondrites as Orgueil (CI), Murchison (CM), Tagish Lake (C2-ungrouped) and EET 92042 (CR), and to a series of coals. The estimate of the aliphatic to aromatic carbon ratio (n CHx/ n Aro ) in IOM samples from Orgueil, Murchison and Tagish Lake chondrites is in good agreement with Single-Pulse/NMR estimates earlier published, and is lower by a factor of 1.3 in the case of the CR chondrite EET 92042 (but the error bars overlap). In contrast, the aliphatic to carbonyl ratio (n CHx /n C=O ) is overestimated for the four chondrites. These discrepancies are likely due to the control of the absorption cross-section of the C=O and C=C bonds by the local molecular environment. Regarding coals, the use of published NMR analyses has brought to light that the integrated cross-section ratio A CHx /A Aro varies with the vitrinite reflectance over an order of magnitude. Here as well, the local oxygen speciation plays a critical control in AAro, which decreases with increasing the vitrinite reflectance. We provide an analytical law that links A CHx /A Aro and vitrinite reflectance, which will allow the determination of n CHx /n Aro for any coal sample, provided its vitrinite reflectance is known.