Nitrogen‐15 Determination of Nonrandomly Distributed Dinitrogen in Air

Abstract

AbstractDinitrogen 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 NOx species, and thereby redistribute the N isotopes of the N2 into an NOx pool. The NOx 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.