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- Title
High-precision measurement of phenylalanine δ<sup>15</sup>N values for environmental samples: A new approach coupling high-pressure liquid chromatography purification and elemental analyzer isotope ratio mass spectrometry.
- Authors
Broek, Taylor A. B.; Walker, Brett D.; Andreasen, Dyke H.; McCarthy, Matthew D.
- Abstract
RATIONALE Compound-specific isotope analysis of individual amino acids (CSI-AA) is a powerful new tool for tracing nitrogen (N) source and transformation in biogeochemical cycles. Specifically, the δ15N value of phenylalanine (δ15NPhe) represents an increasingly used proxy for source δ15N signatures, with particular promise for paleoceanographic applications. However, current derivatization/gas chromatography methods require expensive and relatively uncommon instrumentation, and have relatively low precision, making many potential applications impractical. METHODS A new offline approach has been developed for high-precision δ15N measurements of amino acids (δ15NAA), optimized for δ15NPhe values. Amino acids (AAs) are first purified via high-pressure liquid chromatography (HPLC), using a mixed-phase column and automated fraction collection. The δ15N values are determined via offline elemental analyzer-isotope ratio mass spectrometry (EA-IRMS). RESULTS The combined HPLC/EA-IRMS method separated most protein AAs with sufficient resolution to obtain accurate δ15N values, despite significant intra-peak isotopic fractionation. For δ15NPhe values, the precision was ±0.16‰ for standards, 4× better than gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS; ±0.64‰). We also compared a δ15NPhe paleo-record from a deep-sea bamboo coral from Monterey Bay, CA, USA, using our method versus GC/C/IRMS. The two methods produced equivalent δ15NPhe values within error; however, the δ15NPhe values from HPLC/EA-IRMS had approximately twice the precision of GC/C/IRMS (average stdev of 0.27‰ ± 0.14‰ vs 0.60‰ ± 0.20‰, respectively). CONCLUSIONS These results demonstrate that offline HPLC represents a viable alternative to traditional GC/C/IMRS for δ15NAA measurement. HPLC/EA-IRMS is more precise and widely available, and therefore useful in applications requiring increased precision for data interpretation (e.g. δ15N paleoproxies). Copyright © 2013 John Wiley & Sons, Ltd.
- Subjects
PHENYLALANINE; HIGH performance liquid chromatography; GAS purification; MASS spectrometry; NITROGEN spectra; PALEOCEANOGRAPHY; GAS chromatography
- Publication
Rapid Communications in Mass Spectrometry: RCM, 2013, Vol 27, Issue 21, p2327
- ISSN
0951-4198
- Publication type
Article
- DOI
10.1002/rcm.6695