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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|
|Publisher||Taylor and Francis|
|Pages||516 - 530|
|Keywords||carbon-13, gas chromatography–combustion–isotope ratio mass spectrometry, isotope analysis, soil amino acids, trimethylsilylation|