title: Simplifying and improving the extraction of nitrate from freshwater for stable isotope analyses.
abstract: Determining the isotopic composition of nitrate (NO(3)(-)) in water can prove useful to identify NO(3)(-) sources and to understand its dynamics in aquatic systems. Among the procedures available, the 'ion-exchange resin method' involves extracting NO(3)(-) from freshwater and converting it into solid silver nitrate (AgNO(3)), which is then analysed for (15)N/(14)N and (18)O/(16)O 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 NO(3)(-) (≥ 00 μM or 25 mg L(-1) NO(3)(-)) and low DOC (typically < 17 μM of C or 5 mg L(-1) C) levels. % N analysis revealed that a few AgNO(3) 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 AgNO(3) in order to better assess the type and gravity of the contamination as well as to identify potentially unreliable data.
authors.affiliation: School of Natural Sciences, Geology Department, Centre for the Environment, Trinity College Dublin, Dublin 2, Ireland. eddy.minet@gmail.com
authors.forename: Eddy
authors.initials: E
authors.lastname: Minet
authors.forename: Robbie
authors.initials: R
authors.lastname: Goodhue
authors.forename: Catherine E
authors.initials: CE
authors.lastname: Coxon
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kalin
authors.forename: Wolfram
authors.initials: W
authors.lastname: Meier-Augenstein
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis / Q000737:chemistry; D005591:Chemical Fractionation / Q000379:methods*; D004784:Environmental Monitoring; D005618:Fresh Water / Q000737:chemistry*; D009566:Nitrates / Q000032:analysis* / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000032:analysis / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D002247:Carbon Isotopes; D009566:Nitrates; D009587:Nitrogen Isotopes; D014874:Water Pollutants, Chemical