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This article in SSSAJ

  1. Vol. 62 No. 2, p. 406-412
    Received: Apr 14, 1997

    * Corresponding author(s): mulvaney@uiuc.edu


Diffusion Methods for Automated Nitrogen-15 Analysis using Acidified Disks

  1. S. A. Khan,
  2. R. L. Mulvaney* and
  3. P. D. Brooks
  1. Dep. of Natural Resources and Environmental Sciences, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801
    Dep. of Environmental Science, Policy, and Managemnet, Univ. of California, Berkeley, CA 94720



Diffusion methods are often employed to speciate inorganic N in soil extracts or water for N-isotope analysis with automated mass spectrometers. Diffusion is usually carried out in a plastic specimen container with an acidified filter disk to collect the diffused NH3. Owing to the small size of the container and the limited surface area of the acidified disk, a diffusion period of 6 to 14 d is generally required, and even then recovery may be incomplete. Simple diffusion methods were developed that use two acidified disks in a 473-mL (1-pint) wide-mouth Mason jar. Diffusions with MgO to recover NH4-N, or with MgO plus Devarda's alloy to recover (NH4 + NO3)-N or (NH4 + NO3 + NO2)-N, were performed from 5 to 100 mL of either 2 or 4 M KCl. Quantitative recovery of 150 µg of N was achieved in 1 to 7 d at 20 to 25°C, and in 2 to 14 h by heating on a hot plate at 45 to 50°C. Isotopic analyses of labeled soil extracts were accurate to within 5%, as determined by isotope-dilution calculations. Incomplete diffusion led to <2% error in analysis of NH4-N, whereas serious error occurred in analysis of (NH4 + 15NO3)-N.

This study was a part of Project ILLU-15-0392, Illinois Agric. Exp. Stn.

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