Improved diffusion methods for nitrogen and 15nitrogen analysis of Kjeldahl digests

Simple methods are described that permit the use of either H3BO3 indicator solution or acidified filter disks to collect NH3 liberated by treatment of Kjeldahl digests with NaOH. These methods incorporate modifications to improve reliability, analytical capacity, and convenience. A semimicro digest...

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Bibliographic Details
Published in:Journal of AOAC International 2000-09, Vol.83 (5), p.1039-1046
Main Authors: STEVENS, W. Bart, MULVANEY, Richard L, KHAN, Saeed A, HOEFT, Robert G
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Biological and medical sciences
Diffusion
Filtration
Food industries
Fundamental and applied biological sciences. Psychology
General agronomy. Plant production
General aspects
Generalities. Analysis and diagnosis methods
Hydrolysis
Indicators and Reagents
Methods of analysis, processing and quality control, regulation, standards
Nitrogen - analysis
Nitrogen Isotopes
Soil-plant relationships. Soil fertility. Fertilization. Amendments
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Summary:Simple methods are described that permit the use of either H3BO3 indicator solution or acidified filter disks to collect NH3 liberated by treatment of Kjeldahl digests with NaOH. These methods incorporate modifications to improve reliability, analytical capacity, and convenience. A semimicro digest was diluted to 25 mL with deionized water, and a 10 mL aliquot, containing up to 4 mg N (150 microg N for diffusions into acidified disks), was transferred to a shell vial, which was placed inside a 473 mL (1 pint) Mason jar containing 10 mL 10N NaOH. The NH3 liberated by overturning the vial was collected after 12 to 48 h at ambient temperature, or after 4 h at 45 to 50 degrees C on a hotplate, for quantitative and/or isotope-ratio analyses. With either H3BO3 indicator solution or acidified filter disks, recovery of diffused N was quantitative. Isotope-ratio analyses of diffused N from 15N-labeled chemical, plant, and soil samples were within 3% of analyses using steam distillation.
ISSN:1060-3271
1944-7922
DOI:10.1093/jaoac/83.5.1039