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Equations for Determination of Nitrogen-15 Labeled Dinitrogen and Nitrous Oxide by Mass Spectrometry

Mulvaney, R. L., Boast, C. W.
Soil Science Society of America journal 1986 v.50 no.2 pp. 360-363
computers, denitrification, equations, fertilizers, isotope labeling, mass spectrometry, nitrogen, nitrous oxide, soil, spectrometers, stable isotopes
In mass spectrometric procedures recently developed for determination of ¹⁵N-labeled dinitrogen (N₂) and nitrous oxide (N₂O) evolved from soils, calculations are performed to determine the mole fraction of ¹⁵N in the N pool from which this N₂ or N₂O was derived (¹⁵XN), and a fraction proportional to the amount evolved (d). The equations originally derived for these calculations are based on several approximations and are so simple that they can easily be performed using a handheld calculator. Modern ratio mass spectrometers are usually equipped with an on-line programmable calculator or computer to process the digital output from the integrating ratiometer, which has made it practical to calculate ¹⁵XN and d using equations based on fewer approximations than the equations previously derived. Refined versions of the equations are derived in this paper. The refined equations are much more complicated than the original equations, but they are more accurate and permit the use of fertilizers containing <20 atom % ¹⁵N in studies of denitrification.