Lithium Isotopic Reference
Isotopeamount Ratios of Lithium Isotopic Reference Materials
Description 
NIST RM # 
Material 
Nominal Unit Size 
n(^{6}Li)/n(^{7}Li) 
Footnote 
Ref 
LSVEC 
8545 
lithium carbonate 
0.4 g 
0.082 15 
** 
4 
IRMM015 

lithium carbonate 
50 mg 
21.897 
** 
25 
IRMM016 

lithium carbonate 
1 g 
0.082 121 
** 
26 
** Isotopeamount ratio
Guidelines for Reporting Lithium Delta Values
Guidelines for reporting lithium delta values were published in Atomic weights of the elements 1995, T. B. Coplen. Pure Appl. Chem.,68, 23392359 (1996). [full text  pdf 1347 KB] {TSAW1995.pdf}
Relative lithium isotopeamount ratios in geochemical and environmental studies commonly are reported as δ^{7}Li values in terms of n(^{7}Li)/n(^{6}Li) ratios. It was brought to the attention of the Commission that some laboratories are reporting δ^{6}Li values by using n(^{6}Li)/n(^{7}Li) ratios. This is confusing because (i) δ^{7}Li values are opposite in sign to δ^{6}Li values, (ii) the absolute values of δ^{7}Li and δ^{6}Li are not equal, and (iii) samples with more positive δ values are commonly thought of as being more dense or “heavier,” but samples with more positive δ^{6}Li values are less dense. Therefore, to eliminate possible confusion in the reporting of relative lithium isotopeamount ratio data, the Commission recommended that relative lithium isotopic measurements of all substances be expressed as δ^{7}Li values in terms of n(^{7}Li)/n(^{6}Li) ratios relative to the internationally distributed lithium carbonate isotopic reference material LSVEC (0 ‰).
Reporting of δ^{6}Li values, expressed in terms of n(^{6}Li)/n(^{7}Li) ratios, should be discontinued.
References
4. Qi, H.P., Taylor, P.D.P., Berglund, M., and De Bièvre, P., 1997, Calibrated measurements of the isotopic composition and atomic weight of the natural Li isotopic reference material IRMM016, Int. J. Mass Spectrom. Ion Proc., 171, 263268 (1997).
25. IRMM, Certificate, Isotopic Reference Material IRMM015, Institute of Reference Materials and Measurements, Geel, Belgium (2005).
26. IRMM, Certificate, Isotopic Reference Material IRMM016, Institute of Reference Materials and Measurements, Geel, Belgium (2005).
