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Labelled microbial culture as a calibration medium for 13 C‐isotope measurement of derivatized compounds: application to tert ‐butyldimethylsilyl amino acids
Author(s) -
Kheirbeik Louay,
Hatté Christine,
Balesdent Jérôme
Publication year - 2016
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7678
Subject(s) - chemistry , analyte , amino acid , carbon fibers , mass spectrometry , isotope ratio mass spectrometry , gas chromatography , isotopes of carbon , chromatography , gas chromatography–mass spectrometry , carbon 13 , calibration , isotope , environmental chemistry , total organic carbon , biochemistry , materials science , physics , statistics , mathematics , quantum mechanics , composite number , composite material
Rationale 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. Methods 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. Results 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. Conclusions 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.