Simultaneous Determination of Argon and Nitrogen

Glen E. Martin, Daniel D. Snow, Euisik Kim, Roy F. Spalding

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Abstract

Denitrification can be confirmed by the presence of excess N2 as indicated by measurement of argon and nitrogen. Previously reported Ar/N2 ratios in ground water have been measured by static gas mass spectrometry, quadrupole mass spectrometry, and gas chromatography. The detector geometry and flared flight tube of the VG Optima isotope ratio mass spectrometer (IRMS) were determined to be fortuitously engineered for the simultaneous and highly precise measurement of Ar (mass 40) and N2+ (mass 28). Certified gas mixtures containing known Ar/N2 ratios were analyzed to assess instrument accuracy. A preparation system for the extraction and purification of Ar and N2 from water samples was developed and tested. δ(Ar/N2) values for prepared air‐saturated water (ASW) samples (24°C) averaged + 1149 ± 8‰ and did not significantly differ from the predicted value relative to atmospheric Ar/N2 of + 1144‰) (p < 0.001). The δ(Ar/N2) from in situ microcosms averaged +1280 ± 22‰ versus atmospheric Ar/N2 and approximated the expected level for ASW of + 1218 at 12°C. Much lower δ5(Ar/N2) values were measured in 18 ground‐water samples collected from a site where denitrification had previously been documented. Samples collected from a site where conditions indicate little or no denitrification have δ(Ar/N2) values close to those for ASW.

Original languageEnglish (US)
Pages (from-to)781-785
Number of pages5
JournalGroundwater
Volume33
Issue number5
DOIs
StatePublished - Sep 1995

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ASJC Scopus subject areas

  • Water Science and Technology
  • Computers in Earth Sciences

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