Measurement of delta C-13 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 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
• DOI: https://doi.org/10.1080/10256016.2014.959444
• Keywords: carbon-13, gas chromatography–combustion–isotope ratio mass spectrometry, isotope analysis, soil amino acids, trimethylsilylation
• Publisher URL: https://www.tandfonline.com/doi/abs/10.1080/10256016.2014.959444