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This article in SSSAJ

  1. Vol. 57 No. 4, p. 981-988
     
    Received: July 24, 1992


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doi:10.2136/sssaj1993.03615995005700040017x

Automated Determination of Nitrogen-15-Labeled Dinitrogen and Nitrous Oxide by Mass Spectrometry

  1. R. J. Stevens ,
  2. R. J. Laughlin,
  3. G. J. Atkins and
  4. S. J. Prosser
  1. Dep. of Agriculture for Northern Ireland, Newforge Lane, Belfast, BT9 5PX, UK
    Europa Scientific Ltd., Electra Way, Crewe, CW1 1ZA, UK

Abstract

Abstract

The 15N content of N2 and N2O emitted from 15N-enriched soils conveys information about their sources; such information can only be obtained by mass spectrometry. Conventional dual-inlet isotoperatio mass spectrometry (IRMS) involve complex gas sampling and inlet systems, which limit the use of the technique. Continuous-flow IRMS was evaluated for the automated analysis of 15N-labeled N2 or N2O. A gas sample is flushed from a vial by a He carrier stream. Carbon dioxide, NO, and water are chemically removed prior to chromatographic separation of N2 from N2O. For N2 analysis, the carrier stream is passed through a Cu reduction column to remove O2. A triple-collector isotope-ratio mass spectrometer analyzes a portion of the carrier stream for N2 at m/z 28, 29, and 30. Accurate values for ratio (29/28 and 30/28) differences in normal and enriched atmospheres were obtained from enrichments up to 2 atom % 15N with coefficients of variation (CVs) ranging from 0.07 to 1.37%. The reduction column is bypassed for the analysis of N2O at m/z 44, 45, and 46. From the 45/44 ratios, the 15N content of the N2O could be determined accurately with enrichments up to 40 atom %. Precision depended on concentration and enrichment, with CVs ranging from 10% for 15 µL N2O L−1 at natural abundance to <1% for 100 µL N2O L−1 at 10 atom % 15N. The concentration of N2O could be quantified from the ion currents at m/z 44, 45, and 46 with a detection limit of 2.1 µL N2O L−1. A batch of 132 samples can be analyzed automatically for N2 or N2O at a rate of six determinations per hour. Automation of 15N determination in N2 and N2O should aid the study of the processes resulting in evolution of these gases from soil.

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