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Measurement of delta C-13 values of soil amino acids by GC-C-IRMS using trimethylsilylation: a critical assessment


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 d13C 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 d13C for di-, tri- and tetra-TMS derivatives.

For soil samples, only four amino acids (leucine, valine, threonine and serine) provide reliable d13C values with a total average uncertainty of 1.3 ‰. We conclude that trimethylsilyl derivatives are only suitable for determining the 13C incorporation in amino acids within experiments using 13C-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.

Acceptance Date Jul 23, 2014
Publication Date Oct 21, 2014
Journal Isotopes in Environmental and Health Studies
Print ISSN 1025-6016
Publisher Taylor and Francis
Pages 516 - 530
Keywords carbon-13, gas chromatography–combustion–isotope ratio mass spectrometry, isotope analysis, soil amino acids, trimethylsilylation
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