Simplifying and improving the extraction of nitrate from freshwater for stable isotope analyses

Eddy Minet, Robbie Goodhue, Catherine E. Coxon, Robert M. Kalin, Wolfram Meier-Augenstein

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Abstract

Determining the isotopic composition of nitrate (NO3_) in water can prove useful to identify NO3_ sources and to understand its dynamics in aquatic systems. Among the procedures available, the ‘ionexchange resin method’ involves extracting NO3_ from freshwater and converting it into solid silver nitrate (AgNO3), which is then analysed for 15N/14N and 18O/16O ratios. This study describes a simplified methodology where water was not pre-treated to remove dissolved organic carbon (DOC) or barium cations (added to precipitate O-bearing contaminants), which suited samples with high NO3_ ($400 mM or 25 mg L_1 NO3_) and low DOC (typically <417 mM of C or 5 mg L_1 C) levels. % N analysis revealed that a few AgNO3 samples were of low purity (compared with expected % N of 8.2), highlighting the necessity to introduce quality control/quality assurance procedures for silver nitrate prepared from field water samples. Recommendations are then made to monitor % N together with % O (expected at 28.6, i.e. 3.5 fold % N) in AgNO3 in order to better assess the type and gravity of the contamination as well as to identify potentially unreliable data.
Original languageEnglish
Pages (from-to)2062-2066
Number of pages5
JournalJournal of Environmental Monitoring
Volume13
Issue number7
Early online date31 May 2011
DOIs
Publication statusPublished - 2011

Keywords

  • nitrate
  • freshwater
  • isotope analysis
  • ionexchange resin method’

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