title: Measurement of δ13C values of soil amino acids by GC-C-IRMS using trimethylsilylation: a critical assessment.
abstract: In this study, we evaluated trimethylsilyl (TMS) derivatives as derivatization reagents for the compound-specific stable carbon isotope analysis of soil amino acids by gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). We used non-proteinogenic amino acids to show that the extraction-derivatization-analysis procedure provides a reliable method to measure δ(13)C values of amino acids extracted from soil. However, we found a number of drawbacks that significantly increase the final total uncertainty. These include the following: production of multiple peaks for each amino acid, identified as di-, tri- and tetra-TMS derivatives; a number of TMS-carbon (TMS-C) atoms added lower than the stoichiometric one, possibly due to incomplete combustion; different TMS-C δ(13)C for di-, tri- and tetra-TMS derivatives. For soil samples, only four amino acids (leucine, valine, threonine and serine) provide reliable δ(13)C values with a total average uncertainty of 1.3 ‰. We conclude that trimethylsilyl derivatives are only suitable for determining the (13)C incorporation in amino acids within experiments using (13)C-labelled tracers but cannot be applied for amino acids with natural carbon isotope abundance until the drawbacks described here are overcome and the measured total uncertainty significantly decreased.
authors.affiliation: a Dipartimento di Matematica e Fisica , Seconda Università di Napoli , Caserta , Italy.
authors.forename: Mauro
authors.initials: M
authors.lastname: Rubino
authors.forename: Sylvie
authors.initials: S
authors.lastname: Milin
authors.forename: Antonio
authors.initials: A
authors.lastname: D'Onofrio
authors.forename: Patrick
authors.initials: P
authors.lastname: Signoret
authors.forename: Christine
authors.initials: C
authors.lastname: Hatté
authors.forename: Jérôme
authors.initials: J
authors.lastname: Balesdent
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002138:Calibration; D002247:Carbon Isotopes / Q000032:analysis / Q000378:metabolism*; D004784:Environmental Monitoring / Q000379:methods*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D010944:Plants / Q000378:metabolism*; D012680:Sensitivity and Specificity; D012987:Soil / Q000737:chemistry; D014297:Trimethylsilyl Compounds; D035501:Uncertainty
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D012987:Soil; D014297:Trimethylsilyl Compounds
keywords: carbon-13; gas chromatography–combustion–isotope ratio mass spectrometry; isotope analysis; soil amino acids; trimethylsilylation