title: Labelled microbial culture as a calibration medium for (13) C-isotope measurement of derivatized compounds: application to tert-butyldimethylsilyl amino acids.
abstract: Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is widely used in studies of environmental or biological functioning. In the case of derivatized molecules, a calibration might be required due to added non-analyte carbon and in some cases non-stoichiometric recovery by the mass spectrometer.
  
  
  
  Two biological materials of known isotopic composition were produced by microbial cell cultures on either (13) C-labelled glucose or non-labelled glucose as sole source of carbon. Subsequent hydrolyzed amino acids were derivatized as tert-butyldimethylsilyl (tBDMSi) derivatives and analyzed by GC/C/IRMS. The (13) C-enrichment measurements were used as a direct calibration to calculate the original (13) C/(12) C ratios of individual amino acids. We tested this calibration on both known and unknown samples.
  
  
  
  For the main proteinogenic amino acids we could determine the number of non-analyte added carbon atoms and assess the non-stoichiometrical recovery of tBDMSi carbon atoms, due to their incomplete oxidation in the combustion step of GC/C/IRMS. The calibration enabled the determination of the natural abundances (δ(13) C values) of amino acids with an average accuracy of ±1.1 ‰. We illustrate the application of the calibration to determine the (13) C/(12) C ratios of amino acids, and the associated uncertainty, in biological and plant materials.
  
  
  
  The analysis of a labelled microbial cell culture offers a straightforward, rapid and reliable estimate of non-analyte carbon contribution to stable isotope composition. We recommend this method as a calibration or a control in artificial or natural (13) C-tracing experiments. Copyright © 2016 John Wiley & Sons, Ltd.
authors.affiliation: Aix-Marseille-Universite, CNRS, College de France, IRD, INRA, CEREGE UM34, 13545, Aix-en-Provence, France.
authors.forename: Louay
authors.initials: L
authors.lastname: Kheirbeik
authors.affiliation: Laboratoire des Sciences du Climat et de l'Environnement, UMR 8212 CEA-CNRS-UVSQ, F-91198, Gif-sur-Yvette, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Hatté
authors.affiliation: Aix-Marseille-Universite, CNRS, College de France, IRD, INRA, CEREGE UM34, 13545, Aix-en-Provence, France.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Balesdent
mesh_terms: D000596:Amino Acids / Q000737:chemistry* / Q000378:metabolism; D018533:Biomass; D002138:Calibration; D002247:Carbon Isotopes / Q000032:analysis* / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D017646:Organosilicon Compounds / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D017646:Organosilicon Compounds; C009660:t-butyldimethylsilyl compounds