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U.S. Department of Energy
Office of Scientific and Technical Information

Division S-3-soil microbiology and biochemistry

Journal Article · · Soil Sci. Soc. Am. J.; (United States)
OSTI ID:6645690
Steam distillation methods are commonly used to prepare Kjeldahl digests for N stable isotope analysis. Steam distillation requires skilled operation of specialized equipment as well as considerable operator time, and is subject to sample cross contamination unless precautionary washing procedures are adopted. A simple inexpensive, labor saving diffusion method for Kjeldahl digests using disposable polypropylene specimen containers (128 mL) with threaded lids was devised to overcome problems with steam distillation. Diffused ammonia was collected in a disposable test tube (12 by 75 mm) containing an acid trap. Fractionation of N stable isotopes was <1% for diffused diluted simulated Kjeldahl digests, even when <20% of the initial NH/sub 3/ present was diffused. As diffusion becomes more complete isotope fractionation decreases. Direct comparison of aliquots of the same plant tissue Kjeldahl digest by steam distillation and diffusion over a wide range of /sup 15/N enrichments (0.36-43.3 atom %) indicated that deviation of the two methods was about 1%. The /sup 15/N enrichment of diffused samples was consistently slightly less than that of steam distilled samples. The method is recommended for research using /sup 15/N enriched or depleted sources, but not for research measuring natural variation in /sup 15/N abundance, unless complete diffusion is assured.
Research Organization:
Univ. of Kentucky, Lexington
OSTI ID:
6645690
Journal Information:
Soil Sci. Soc. Am. J.; (United States), Journal Name: Soil Sci. Soc. Am. J.; (United States) Vol. 51:1; ISSN SSSJD
Country of Publication:
United States
Language:
English