![]() ![]() Isotope reference materials are generated, maintained, and sold by the International Atomic Energy Agency ( IAEA), the National Institute of Standards and Technology ( NIST), the United States Geologic Survey ( USGS), the Institute for Reference Materials and Measurements ( IRMM), and a variety of universities and scientific supply companies. Due to their critical role in measuring isotope ratios, and in part, due to historical legacy, isotopic reference materials define the scales on which isotope ratios are reported in the peer-reviewed scientific literature. Without isotope references, measurements by mass spectrometry would be much less accurate and could not be used in comparisons across different analytical facilities. By measuring a material of known isotopic composition, fractionation within the mass spectrometer can be removed during post-measurement data processing. Moreover, the degree of instrument fractionation changes during measurement, often on a timescale shorter than the measurement's duration, and can depend on the characteristics of the sample itself. As a result, the isotopic ratio that the instrument measures can be very different from that in the sample's measurement. Isotopic references are used because mass spectrometers are highly fractionating. Isotopic reference materials are compounds ( solids, liquids, gasses) with well-defined isotopic compositions and are the ultimate sources of accuracy in mass spectrometric measurements of isotope ratios. Materials with a well-defined isotopic composition
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