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Stable Isotopes

Nitrogen Isotopes


Nitrogen has two naturally occurring stable isotopes (14N and 15N). For studies of stable isotope biogeochemistry we measure the ratio of 15N to 14N in samples of interest, expressed relative to the ratio in a standard of known isotopic composition, such as atmospheric air (15N/14N = 0.0036765 (1) (2)).

Formual for delta 15N

The d15N values of terrestrial nitrogen samples typically range from -25 to +30 per mil (parts per thousand) relative to air(3).

Isotope Atomic mass
Natural abundance
(atom %)
14N 14.003074002 99.632
15N 15.00010897 0.368

See the WebElements page on the Isotopes of Nitrogen
and the Chart of the Nuclides centered on N.

(1)From Table 9-1, p. 154, of David P. Mattey, 1997, Gas source mass spectrometry: isotopic composition of lighter elements, pages 154-170 in Robin Gill (editor), Modern Analytical Geochemistry, Longman (UK).

(2)The uncertainty in this value is much larger than the precision with which we can measure relative ratios, which is one reason for the use the "delta" notation; page 32 in Robert E. Criss, 1999, Principles of Stable Isotope Distribution, Oxford University Press.

(3)From Figure 2-29, p. 113, of Arthur H. Brownlow, 1996, Geochemistry, Prentice-Hall.

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January 2009