New methods for nitrogen stable isotope measurements of amino acids: Applications to marine ecological studies

摘要: Compound specific isotope analysis of individual amino acids (CSI-AA) is a powerful tool for tracing nitrogen (N) source and transformation in biogeochemical cycles. Specifically, the d15N value phenylalanine (d15NPhe) represents an increasingly used proxy baseline values, with particular promise paleoceanographic applications. Further, multiple studies have shown that values Phe glutamic acid (Glu) can be coupled to provide precise estimates trophic position (TP), while simultaneously decoupling from effects transfer. However, current derivatization/gas chromatography (GC) methods require expensive relatively uncommon instrumentation, low precision, posing significant issues many potential Here we present new approach CSI-AA based on high-pressure liquid (HPLC) purification underivatized acids, followed by offline elemental analysis-isotope ratio mass spectrometry (EA-IRMS). The utility this demonstrated two different applications using natural materials: 1) construction high precision record d15NPhe proteinaceous coral tissue 2) TP estimation five marine organisms Glu Phe. Both demonstrations were compared measured established GC method. In all cases both produced equivalent however, generated HPLC/EA-IRMS had higher average cases. These results demonstrate viable alternative traditional d15NAA measurement may therefore allow expansion applications, requiring only commonly available instrumentation produce values.