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This article in SSSAJ

  1. Vol. 66 No. 3, p. 1008-1011
    Received: May 28, 2001

    * Corresponding author(s): mulvaney@uiuc.edu
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A technique to facilitate diffusions for nitrogen-isotope analysis by direct combustion

  1. K. K. Moran,
  2. R. L. Mulvaney * and
  3. S. A. Khan
  1. Dep. of Natural Resources and Environ. Sci., Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801


A technique was developed that permits the use of boric acid-indicator solution in carrying out diffusions for inorganic 15N analysis of soil extracts by direct combustion, so as to eliminate the need for a separate quantitative determination. In this technique, the titrated sample is acidified with 2.5 M KHSO4 and subsequently treated with methanol to remove H3BO3 The NH+ 4-N is dissolved in 1 mL of deionized water, concentrated after transfer to a microcentrifuge tube, and freeze-dried in a tin capsule. Isotope-ratio analyses were accurate to within 5% when diffusions were performed on 100 to 1000 μg of NH+ 4-N (0.2–10 atom % 15N), whereas errors of 8 to 17% occurred with 25 to 50 μg of labeled N, even after correction for isotopic dilution by atmospheric NH3 The technique described permits 15N analysis of any form of N that can be recovered by H3BO3 diffusion of soil, soil extracts, soil hydrolysates, Kjeldahl digests, water, or wastewater.

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Copyright © 2002. Soil Science SocietyPublished in Soil Sci. Soc. Am. J.66:1008–1011.