A novel tool for stable nitrogen isotope analysis in aqueous samples.
BACKGROUND
Bulk stable isotope analysis (BSIA) of dissolved matter (e.g. dissolved organic carbon, total nitrogen bound (TNb), etc.) is of particular importance since this pool is a prime conduit in the cycling of N and C. Studying the two elemental pools is of importance, as transformation and transport processes of N and C are inextricably linked in all biologically mediated systems. No system able to analyze natural abundance stable carbon and nitrogen isotope composition in aqueous samples (without offline sample preparation) and simultaneously has been reported so far. Extension of the high-temperature combustion (HTC) system, to be capable of measuring TNbstable nitrogen isotope composition, is described in this study.


METHODS
To extend the TOC analyzer to be capable of measuring TNb, modifications from the HTC high-performance liquid chromatography/isotope ratio mass spectrometry (HPLC/IRMS) interface were implemented and expanded. A reduction reactor for conversion of NOxinto N2was implemented into the new developed system. The extension addresses mainly the development of the focusing unit for nitrogen and a degassing device for online separation of TNbfrom molecular nitrogen (N2) prior to injection.


RESULTS
The proof of principle of the system was demonstrated with different compound solutions. In this initial testing, the δ15NAIR-N2values of the tested compounds were determined with precision and trueness of typically ≤0.5‰. Good results (u ≤ 0.5‰) could be achieved down to a TNbconcentration of 40 mgN/L and acceptable results (u ≤ 1.0‰) down to 5 mgN/L. In addition, the development resulted in the first system reported to be suitable for simultaneous and direct δ13C and δ15N BSIA of aqueous samples.


CONCLUSIONS
The development resulted in the first system shown to be suitable for both δ13C and δ15N direct BSIA in aqueous samples. This system could open up new possibilities in SIA-based research fields. Copyright © 2016 John Wiley & Sons, Ltd.
Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.|Instrumental Analytical Chemistry, University of Duisburg-Essen, Universitätsstr. 5, 45141, Essen, Germany.
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http://orcid.org/0000-0002-7979-1671
E
Federherr
Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.
H J
HJ
Kupka
Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Science Park 904, 1098, XH, Amsterdam, The Netherlands.
C
C
Cerli
Institute of Soil Science and Site Ecology, Technical University of Dresden, Pienner Str. 21, 01737, Tharandt, Germany.
K
K
Kalbitz
Research and Innovation, Taunus Instruments GmbH, Berlinerstr. 2, 61267, Neu-Anspach, Germany.
R
R
Dunsbach
Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.
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A
Loos
Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.
M
M
de Reus
Research and Innovation, Elementar Analysensysteme GmbH, Donaustr. 7, 63452, Hanau, Germany.
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L
Lange
Research and Innovation, Isoprime Ltd, Cheadle Hulme, SK8 6PT, UK.
R J
RJ
Panetta
Instrumental Analytical Chemistry, University of Duisburg-Essen, Universitätsstr. 5, 45141, Essen, Germany.
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TC
Schmidt