Reference material USGS26 is aimed at δ15N calibrations.
USGS26 is a dried salt of ammonium sulfate [(NH4)2 SO4]) which was prepared in 1992 by J. K. Böhlke, U.S. Geological Survey [1]. The material was prepared from Fisher ammonium sulfate (A938-500, lot # 915021) and Cambridge Isotopes ammonium sulfate (10% 15N; lot BI 1050) by dissolving and re-crystallizing a mixture of normal reagent salt and 15N enriched salt. The δ15N value of this reference material is the result of the statistical evaluation of interlaboratory comparisons [1,2].
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