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Nitrogen-15 Determination of Nonrandomly Distributed Dinitrogen in Air¹

ABSTRACT

Dinitrogen gas produced by denitrification of ¹⁵N-enriched fertilizers does not achieve a random nitrogen (N) isotope distribution when mixed with atmospheric N₂. Thus, such mixtures cannot be analyzed by the conventional mass spectrometric measurement of the 28 and 29 ion current ratio. A method is proposed which uses a high voltage arc passed between a pair of tungsten electrodes sealed in a glass vessel to fix some of the N₂ as NO_x species, and thereby redistribute the N isotopes of the N₂ into an NO_x pool. The NO_x species are absorbed and oxidized by acidic permanganate, reduced to NH⁺₄, and distilled by routine procedures. Since the are process redistributes the N isotopes randomly by ultimately converting the N to a monatomic species (NH⁺₄), accurate isotope ratio analysis of the distilled samples by the conventional dual-collector mass spectrometer method is possible. The method is precise, accurate, simple, inexpensive, and avoids many of the problems associated with direct ¹⁵N analysis of gas samples with nonrandom N isotopic distributions. This description of the basic methodology may enable direct measurement of denitrification losses from highly labeled fertilizer sources while its application to estimation of total denitrification losses requires additional methodologies not described in this paper.

¹ Contribution from the Agro-Economic Division of the International Fertilizer Development Center (IFDC), Muscle Shoals, AL 35662.

² Soil Scientist, Research Associate, Analytical Chemist, Instrumentation Specialist, Soil Scientist, IFDC, and Visiting Scientist at IFDC, Queensland Wheat Research Inst., Toowoomba, Australia, respectively. The senior author is now Research Program Coordinator, Australian Center for International Agricultural Research, Canberra City, Australia.

Received for publication September 7, 1984. Accepted for publication January 7, 1985.

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