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Nitrogen Isotopic Reference

 δ15N Values of Nitrogen Isotopic Reference Materials

Description 

NIST RM # 

Material

Nominal Unit Size

δ15NAIR

Footnote

Ref

NSVEC

8552

gaseous nitrogen

1 tube,  300 µmol

–2.78 ‰

 

7

IAEA-N-1

8547

ammonium sulfate 

0.4 g 

+0.43 ‰

***

7

IAEA-N-2

8548

ammonium sulfate

0.4 g 

+20.41 ‰

 

7

IAEA-NO-3

8549

potassium nitrate 

0.4 g

+4.72  ‰

 

7

USGS25

8550

ammonium sulfate 

0.4 g 

–30.41 ‰

 

7

USGS26

8551

ammonium sulfate 

0.4 g 

+53.70 ‰

 

7

USGS32

8558

potassium nitrate

0.5 g  

+180 ‰

***

7

USGS34 8568 potassium nitrate 0.6 g -1.8 ‰   27
USGS35 8569 sodium nitrate 0.6 g +2.7 ‰   27
USGS40 8573 L-glutamic acid 1 g -4.52 ‰   28
USGS41 8574 L-glutamic acid 0.5 g +47.57 ‰   28

***  Interim consensus values used for scale normalization

Recommendation on the Reporting of δ15N Measurements

To eliminate possible confusion in the reporting of the nitrogen isotope-amount ratio n(15N)/n(14N), the Commission recommended in 1991 at the 36th General Assembly at Hamburg that the value 272 be employed for the n(14N)/n(15N) value of N2 in air for calculatingn (15N)/n(14N) values.  Such values are sometimes called “atom %” values and this is deprecated usage because “atom %” is not an SI unit; rather, such values are atom fractions or stable isotope abundance fractions.

This recommendation derives from the fact that the Commission's 1983 Table of Isotopic Compositions [full text - pdf 254 KB] {TICE 1983.pdf} rounds the originally reported Junk and Svec (ref. 23) n(14N)/n(15N) value of 272.0 ± 0.3 in atmospheric nitrogen to (99.634 ± 0.001)/(0.366 ± 0.001), which is 272.22.  The difference between 272 and 272.22 corresponds to a difference in δ15N of 0.8 ‰, which is about 10 times the measurement precision of many stable-isotope laboratories.  When converting δ15N values to stable isotope abundance fraction, some authors use 272 and some use 272.22.  The Commission recommends that 272 always be used in this conversion.  The full recommendation appears in:
Reporting of Nitrogen-isotope abundances, Coplen, T. B., Krouse, H. R., and Böhlke, J.K., Pure Appl. Chem., 64, 907-908 (1992). [full text - pdf 118 KB] {N Isotopic Reporting Guidelines.pdf}

References

7. Böhlke, J.K., and Coplen, T.B., Interlaboratory comparison of reference materials for nitrogen-isotope-ratio measurements, in Reference and intercomparison materials for stable isotopes of light elements: Vienna, International Atomic Energy Agency, IAEA-TECDOC-825, 51-66 (1995).
23. Junk, G., and Svec, H. J., The absolute abundance of the nitrogen isotopes in the atmosphere and compressed gas from various sources, Geochim. Cosmochim. Acta, 14, 234-243 (1958).
27. Böhlke, J.K., Mroczkowski, S. J., and Coplen, T. B., Oxygen isotopes in nitrate: new reference materials for 18O:17O:16O measurements and observations on nitrate-water equilibration, Rapid Comm. Mass Spectrom., 17, 1835-1846 (2003).
28. Qi, H., Coplen, T.B., Geilmann, H., Brand, W. A., and Böhlke, J.K., Two new organic reference materials for δ13C and δ15N measurements and a new value for the δ13C of NBS 22 oil: Rapid Comm. Mass Spectrom., 17, 2483-2487 (2003).

 
2010 Commission on Isotopic Abundances and Atomic Weights | a commission of the International Union of Pure and Applied Chemistry