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Practical considerations for amino acid isotope analysis

Silverman, Shaelyn N. and Phillips, Alexandra A. and Weiss, Gabriella M. and Wilkes, Elise B. and Eiler, John M. and Sessions, Alex L. (2022) Practical considerations for amino acid isotope analysis. Organic Geochemistry, 164 . Art. No. 104345. ISSN 0146-6380. doi:10.1016/j.orggeochem.2021.104345.

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Over the last few decades, isotopic analysis of amino acids at the compound- and position-specific levels has been rapidly advancing across diverse fields. As these techniques progress, evaluation of isotopic fractionation associated with sample workup is essential. This critical review of analytical methods through the lens of isotope geochemistry provides a benchmark for researchers across disciplines seeking to make compound- and position-specific amino acid isotope measurements. We focus on preparation, acid hydrolysis, clean-up, derivatization, separation, and C, H, N, and S isotope measurement. Despite substantial customizability across these steps, the following general recommendations should maximize recovery while minimizing isotopic fractionation. Samples should be freeze-dried and stored anoxically at ≤ –20 °C prior to conventional acid hydrolysis (6N HCl, 110 °C, 20–24 h, anoxic), which suffices for many residues. Both gas and liquid chromatographic (GC and LC, respectively) techniques are well-established and separate about 15 amino acids; LC bypasses the need for derivatization, while GC provides higher sensitivity. When derivatization is needed, n-acetyl and alkoxycarbonyl esters provide the most reproducible C isotope ratios. For compound-specific analyses, online GC–IRMS and LC–IRMS systems offer the easiest workflow, but EA–IRMS enables potential multi-element isotope analysis. Emerging techniques like high-resolution mass spectrometry are also promising for multi-element analysis and recover position-specific isotopic information. Looking forward to the next decade of innovation, isotope geochemists and ecologists can improve amino acid isotope analysis by focusing on streamlining multi-element analysis and standardizing calibration practices across laboratories.

Item Type:Article
Related URLs:
URLURL TypeDescription
Phillips, Alexandra A.0000-0001-5959-5238
Weiss, Gabriella M.0000-0002-9571-2558
Wilkes, Elise B.0000-0002-3379-7832
Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2022 Elsevier Ltd. Received 26 February 2021, Revised 10 November 2021, Accepted 19 November 2021, Available online 28 December 2021, Version of Record 14 February 2022. The authors would like to thank Kate Freeman, Sarah Zeichner, and Phillip M. Riekenberg for their helpful feedback on early versions of this review. The authors also acknowledge Karli Holman for her expertise in reviewing proposed acid hydrolysis reactions and thank members of the Sessions and Eiler labs at Caltech and of the Freeman lab at Penn State for their informative discussions with authors, as well as the two anonymous reviewers and the Associate Editor for their constructive comments. This work was supported in part by grants from the NSF GRFP (to SNS, Fellow ID 2018259065), NASA Astrobiology Institute (grant number 80NSSC18M094 to ALS and JME), NSF Geobiology (grant number EAR-1921330 to ALS), the Agouron Institute (grant number AI-F-GB54.19.2 to EBW) and the Simons Foundation (to JME, award number 626103) and DOE (to JME, award number DE-SC0016561). Any opinions, findings, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funding agencies. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Agouron InstituteAI-F-GB54.19.2
Simons Foundation626103
Department of Energy (DOE)DE-SC0016561
Subject Keywords:Amino acids; Compound-specific isotope analysis; Position-specific isotope analysis; Acid hydrolysis; Derivatization; Separation; Isotope ratio mass spectrometry; Orbitrap™; Nuclear magnetic resonance
Record Number:CaltechAUTHORS:20220214-701486900
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Official Citation:Shaelyn N. Silverman, Alexandra A. Phillips, Gabriella M. Weiss, Elise B. Wilkes, John M. Eiler, Alex L. Sessions, Practical considerations for amino acid isotope analysis, Organic Geochemistry, Volume 164, 2022, 104345, ISSN 0146-6380,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:113444
Deposited By: Tony Diaz
Deposited On:14 Feb 2022 21:27
Last Modified:05 Apr 2022 17:22

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