Liquid Chromatographic Isolation of Individual Amino Acids Extracted From Sediments for Radiocarbon Analysis

Abstract

The "building blocks of life" are found nearly ubiquitously in the environment in the form of proteins, peptides, and single amino acids. To shed light on amino acid sources, cycling, and preservation in sedimentary environments, we present a method using high-pressure liquid chromatography to separate and isolate underivatized amino acids extracted from sediments to conduct compound-specific radiocarbon analysis. This method consists of three main steps including (1) amino acid extraction by hydrofluoric and hydrochloric acids followed by desalting, (2) liquid chromatographic isolation and purification using two complementary column chemistries, and (3) post-purification and measurement by accelerator mass spectrometry. The resulting blank of this procedure is estimated to contain 2.2 ± 1.3 µgC with 0.25 ± 0.09 Fm.

High‐precision measurement of phenylalanine and glutamic acid δ15N by coupling ion‐exchange chromatography and purge‐and‐trap continuous‐flow isotope ratio mass spectrometry

“…Metal ions (presumably magnesium and iron) present in sinking particles and sediments need to be removed before IC analysis; otherwise they would form a precipitate with NaOH (mobile phase) and clog the IC column (see later). This step is accomplished using cation‐exchange resin, similar to the desalting procedure employed using the GC/C/IRMS approach 52,56–58 and other studies that need to purify AAs 45 . The resin cleanup step did not affect the subsequent N isotope analysis as verified by previous studies 52,56 .…”

“…This study shares the same sample preparation procedures (steps 1 and 2 in Figure 1) as the GC/C/IRMS 5–7,52 and HPLC approach for isotope analysis of individual AAs 34,41,43–45 . The extraction of AAs from proteinaceous samples followed previously established procedures 1,53,54 .…”

“…Collecting underivatized AAs using preparative liquid chromatography for N isotope measurements have previously been developed 2,3,39,40 . Recent improvements in high‐performance liquid chromatography (HPLC) and column technologies have greatly simplified the procedures for δ 15 N 34,39–42 and radiocarbon 43–45 analysis of individual AAs by pairing with elemental analyzer‐IRMS (EA‐IRMS) and accelerator mass spectrometry, respectively. Recent examples using the HPLC/EA/IRMS approach reported better precision on CSIA‐δ 15 N‐AA than the GC/C/IRMS approach 34,41,42 .…”

Theoretical Amino Acid-Specific Radiocarbon Content in the Environment: Hypotheses to Be Tested and Opportunities to Be Taken

“…With methods for amino acid-specific radiocarbon now developed for biological (Ishikawa et al, 2018) and earthen (Blattmann et al, 2020) samples, we share our thoughts on the merits of what we see as a promising next analytical frontier. Radiocarbon isotopic composition of individual compounds reflects a combination of influences stemming from aging, mixing, reservoir effects, etc.…”

“…To this end, amino acid-specific radiocarbon can offer new perspectives in this ongoing debate. Method developments have also opened up this frontier of amino acid-specific radiocarbon in sediments to exploration (Blattmann et al, 2020).…”