Diffusion methods for automated nitrogen-15 analysis using acidified disks

• Published in: Soil Science Society of America journal Vol. 62; no. 2; pp. 406 - 412
• Main Authors: Khan, S.A. (Univ. of Illinois, Urbana, IL.), Mulvaney, R.L, Brooks, P.D
• Format: Journal Article
• Language: English
• Published: Madison, WI Soil Science Society of America 01.03.1998; American Society of Agronomy
• Subjects: Acids; Agronomy. Soil science and plant productions; AMMONIUM COMPOUNDS; AMMONIUM NITROGEN; ANALYTICAL METHODS; ANIONS; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; CONTAINERS; DETERMINATION; DIFFUSION; Earth sciences; Earth, ocean, space; EVALUATION; Exact sciences and technology; FILTERS; Fundamental and applied biological sciences. Psychology; Geochemistry; JARS; MEASUREMENT; Mineral components. Ionic and exchange properties; NITRATES; NITRITE; NITRITES; NITROGEN; NITROGEN CONTENT; Physics, chemistry, biochemistry and biology of agricultural and forest soils; RADIOISOTOPES; RECOVERY; Scientific imaging; Soil and rock geochemistry; Soil science; SOIL TESTING; Soils; STABLE ISOTOPES; Isotopic analysis; SOIL BIOLOGY; Ammonium; Technical progress; Gaseous diffusion; Mason jar; Samplings; Laboratory measurement; Nitrates; SOIL CHEMISTRY; Nitrogen Isotopes; Inorganic compound; Soil science; Disk; Acid medium; Labelled compound; Method study; Analytical chemistry; N-15; Nuclear chemistry; Filter paper; Experimental study; Nitrogen cycle; Analysis method; Automatic analysis; Nitrogen dioxide; Mass spectrometry
• ISSN: 0361-5995; 1435-0661
• DOI: 10.2136/sssaj1998.03615995006200020017x

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 micrograms of N was achieved in 1 to 7 d at 20 to 25 degrees C, and in 2 to 14 h by heating on a hot plate at 45 to 50 degrees 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