Determination of arginine δ15N values in plant and animal proteins by gas chromatography-combustion-isotope ratio mass spectrometry

Iain P Kendall, Richard P Evershed*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Nitrogen stable isotope techniques are widely used in ecology, archaeology and forensic science to explore trophic relationships and provenances of organisms and materials, most widely using bulk δ15N values of whole organisms, tissues or other materials. However, compound-specific isotope values can provide more diagnostic isotope “fingerprints” and specific information about metabolic processes. Existing techniques for nitrogen isotope analysis allow the determination of δ15N values of 14 amino acids (AAs), accounting for ca. 75% of plant protein and collagen N. The majority of remaining N is from arginine, comprising 16% and 14% of collagen and plant protein N, respectively. We therefore aimed to develop a method to detect arginine and determine its δ15N value (δ15NArg) by GC-C-IRMS, to further contribute to the understanding of metabolic routing of this important AA. We demonstrate that arginine, as its N-acetyl isopropyl ester, is amenable to GC analysis using a 15 m mid-polarity DB 35 column, eluting with baseline resolution from other AAs. The recorded δ15N value by GC C IRMS was within error of that of the underi-vatized compound determined by EA-IRMS. The newly-developed GC C IRMS method was applied to modern plant protein and cattle collagen, enabling their δ15NArg values to be related to AA biosynthesis. Determinations of archaeological cattle collagen δ15NArg values confirmed the suitability of this method to provide further insights into past diets and ecosystems. Bulk collagen δ15N value reconstruction including δ15NArg values better reflect measured bulk values, as the isotopic ratio of 91‰ of collagen N can now be determined at the compound-specific level
Original languageEnglish
JournalAnalytical Chemistry
DOIs
Publication statusAccepted/In press - 24 Aug 2020

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