DOI 10.1515/pac-2013-1023      Pure Appl. Chem. 2014; 86(3): 425–467

Assessment of international reference materials for isotope-ratio analysis (IUPAC Technical Report)1 Abstract: Since the early 1950s, the number of international measurement standards for anchoring stable isotope delta scales has mushroomed from 3 to more than 30, expanding to more than 25 chemical elements. With the development of new instrumentation, along with new and improved measurement procedures for studying naturally occurring isotopic abundance variations in natural and technical samples, the number of internationally distributed, secondary isotopic reference materials with a specified delta value has blossomed in the last six decades to more than 150 materials. More than half of these isotopic reference materials wer