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This article in SSSAJ

  1. Vol. 56 No. 4, p. 1151-1154
     
    Received: Oct 21, 1991


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doi:10.2136/sssaj1992.03615995005600040024x

Diffusion of Kjeldahl Digests for Automated Nitrogen-15 Analysis by the Rittenberg Technique

  1. Y. P. Liu and
  2. R. L. Mulvaney 
  1. Dep. of Agronomy, 1102 S. Goodwin Ave., Univ. of Illinois, Urbana, IL 61801

Abstract

Abstract

Nitrogen-isotope analysis by the Rittenberg technique requires N in the form of NH4. Conversion of organic N to NH4-N is normally accomplished by the Kjeldahl method, which involves digestion with concentrated H2SO4. A diffusion method recently developed for isotope-ratio analysis of inorganic N in soil extracts was modified for use with Kjeldahl digests. An aliquot of the digest (to 20 mL) containing 50 to 150 µg of N was neutralized by overturning a vial with 2 mL of 20 M NaOH in a 118-mL specimen container sealed with a screw-top lid, and the NH3 liberated was collected for 6 d at room temperature in a 7-mm-diam. glass-fiber disk acidified with 10 µL of 1 M H2SO4. For automated Rittenberg analysis of the diffused NH3-N by mass spectrometry, the glass disk was tranferred to a plastic sample tray (96 samples per tray), treated with 10 µL of 28.9 M (concentrated) HF, and dried in a desiccator over anhydrous CaSO4. Studies showed that diffusion was complete (>97%) and that, when correction was made for isotopic dilution by natural-abundance N in reagents, isotope-ratio analyses of diffused N (0.2–4.2 atom % 15N) were in close agreement with analyses using conventional steam-distillation and concentration techniques.

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

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