25 No. 2
Variations of Selected Elements
(IUPAC Technical Report)
T. B. Coplen, J. K. B öhlke, P. DeBiévre, T. Ding,
N. E. Holden, J. A. Hopple, H. R. Krouse, A. Lamberty, H.
S. Peiser, K. Révész, S. E. Rieder, K. J. R.
Rosman, E. Roth, P. D. P. Taylor, R. D. Vocke, Jr., and Y.
and Applied Chemistry,
Vol. 74, No. 10, pp. 1987-2017 (2002)
variations in the isotopic compositions of some chemical elements
are responsible for expanded uncertainties in the standard
atomic weights published by IUPACs Commission on Atomic
Weights and Isotopic Abundances. This report summarizes reported
variations in the isotopic compositions of 20 elements due
to physical and chemical fractionation processes (not due
to radioactive decay) and their effects on the standard atomic
weight uncertainties. For 11 of those elements (hydrogen,
lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur,
chlorine, copper, and selenium), standard atomic-weight uncertainties
have been assigned values that are substantially larger than
analytical uncertainties because of common isotope-abundance
variations in materials of natural terrestrial origin. For
two elements (chromium and thallium), recently reported isotope-abundance
variations potentially are large enough to result in future
expansion of their atomic weight uncertainties. For seven
elements (magnesium, calcium, iron, zinc, molybdenum, palladium,
and tellurium), documented isotope variations in materials
of natural terrestrial origin are too small to have a significant
effect on their standard atomic-weight uncertainties.
compilation indicates the extent to which the atomic weight
of an element in a given material may differ from the standard
atomic weight of the element. For most elements given above,
data are graphically illustrated by a diagram in which the
materials are specified in the ordinate and the compositional
ranges are plotted along the abscissa in scales of (1) atomic
weight, (2) mole fraction of a selected isotope, and (3) delta
value of a selected isotope ratio.
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