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A high-resolution analyser for the measurement of ammonium in oligotrophic seawater

Record type: Article

In this work, we describe a high-resolution fluorometric shipboard analyser and an improved method to determine NH4+ in oligotrophic seawater. The limit of detection is <5 nM, calculated with 95% confidence level using the weighted regression line applied to the standard addition method using real samples prepared with low nutrient seawater from the Atlantic. The results are summarised and cross-compared with spiked artificial seawater (ASW) and spiked Milli-Q water samples. The analyser has a precision of ±1–4% with a high performance over a wide range from 5 nM to 25 ?M. The methodology of NH4+ analysis is based on the fluorescent product formed between o-pthaldialdehyde and NH4+ in the presence of sulfite. Due to the high resolution of the developed system, we were able to study in depth the sensitivity of the method to salinity, amines, amino acids and potential interferences from particles/algae. The method was found to be sensitive to salinity variations, reducing the signal by up to 85% at 5 nM; this effect decreased at higher concentrations of ammonium. It was noted that the interference from amines at low concentrations was negligible; however, at either high amino acid or high amine concentrations, the signal was depressed. To test for the effect of particles on the system, the system was tested with samples containing phytoplankton (Dunaliella primolecta) cells at different concentrations prepared with ASW to simulate the effect of a phytoplankton bloom. This experiment assessed the potential impact of both particles and other potential fluorescence interferences from cells and/or ammonium leaching from cells. This experiment showed that a phytoplankton bloom could potentially have an impact of up to 12% on the signal of interest. Thus, we propose that this method is suitable for oligotrophic environments rather than coastal and eutrophic environments. The reagent was found to be stable for 17 days and standards of 1 ?M were stable for 6 days under laboratory conditions. The developed analyser was successfully demonstrated in the North Atlantic Ocean, in an area of oligotrophic, low NH4+ oceanic waters.

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Citation

Abi Kaed Bey, Samer K., Connelly, Douglas P., Legiret, François-Eric, Harris, Andy J.K. and Mowlem, Matthew C. (2011) A high-resolution analyser for the measurement of ammonium in oligotrophic seawater Ocean Dynamics, 61, (10), pp. 1555-1565. (doi:10.1007/s10236-011-0469-5).

More information

Published date: 2011
Keywords: Ammonium, Shipboard, Analyser, Fluorometric, Resolution
Organisations: Ocean Biochemistry & Ecosystems, Marine Geoscience, Ocean Technology and Engineering

Identifiers

Local EPrints ID: 201063
URI: http://eprints.soton.ac.uk/id/eprint/201063
ISSN: 1616-7341
PURE UUID: 5cf92b71-7303-44e0-b2d4-928a35b4866e

Catalogue record

Date deposited: 25 Oct 2011 09:04
Last modified: 18 Jul 2017 11:13

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Contributors

Author: Samer K. Abi Kaed Bey
Author: Douglas P. Connelly
Author: François-Eric Legiret
Author: Andy J.K. Harris

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