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As isotope-ratio mass spectrometry (IRMS) spread into hydrology, biology, and other fields, computer-controlled instruments became available commercially in the late 1970s and early 1980s. These instruments were constructed in university laboratories, and a substantial effort went into the design and maintenance of these manually operated instruments. In the early 1950s, stable isotope mass spectrometers were not available commercially.
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This material was used for years as a reference material for stable carbon and oxygen isotopes in carbonate samples. Consequently, they collected a substantial amount of material and milled it until it was finely ground. However, this uniformity is exactly what is needed for stable isotopic reference materials. By analyzing relative oxygen-18 abundances, they discovered to their disappointment that the material was relatively uniform in oxygen isotopic abundance.
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The raw carbonate material (Cretaceous belemnite guards) was initially sampled by Heinz Lowenstam and Harold Urey during a field trip to the Peedee formation in South Carolina. The carbon and oxygen isotopic reference material PDB (Peedee belemnite) is a good example. Locally produced isotopic reference materials were disseminated to new research groups to enable results traceable to a common origin. They emerged from the few laboratories that started performing isotopic measurement, mostly in the geosciences. Reference materials for use in differential measurements of stable isotope-number ratio (often shortened to “isotope ratio”) determination have been used since the early 1950s. Keywords: delta notation delta values geochemistry inductively coupled plasma (ICP) mass spectrometry isotopes IUPAC Inorganic Chemistry Division mass spectrometry reference materials 1 Introduction It is recommended that authors publish the delta values of internationally distributed, secondary isotopic reference materials that were used for anchoring their measurement results to the respective primary stable isotope scale. Nevertheless, even primary international measurement standards for isotope-delta measurements are still needed for some elements, including Mg, Fe, Te, Sb, Mo, and Ge. The number of isotopic reference materials for other, heavier elements has grown considerably over the last decade. More than half of these isotopic reference materials were produced for isotope-delta measurements of seven elements: H, Li, B, C, N, O, and S. 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. 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.