Reference materials for stable isotope analysis

Isotopic reference materials are compounds (<a href="/facts/Solid/hj5UsXno">solids</a>, <a href="/facts/Liquid/t9GkLWzt">liquids</a>, <a href="/facts/Gas/hVVAoodV">gasses</a>) with well-defined <a href="/facts/Isotope/KD9B1y6o">isotopic</a> compositions and are the ultimate <a href="/facts/Certified_reference_materials/a8aSXwoL">sources</a> of <a href="/facts/Accuracy_and_precision/JQ47xXDq">accuracy</a> in <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometric</a> measurements of <a href="/facts/Stable_isotope_ratio/vgcdxgjA">isotope ratios</a>. Isotopic references are used because <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometers</a> are highly <a href="/facts/Isotope_fractionation/QUJoofKt">fractionating</a>. As a result, the <a href="/facts/Natural_abundance/dGjaAwc9">isotopic ratio</a> that the instrument measures can be very different from that in the sample's measurement. Moreover, the degree of instrument fractionation changes during measurement, often on a timescale shorter than the measurement's duration, and can depend on the <a href="/facts/Matrix_(mass_spectrometry)/PDX7enqp">characteristics of the sample itself</a>. By measuring a material of known isotopic composition, fractionation within the <a href="/facts/Mass_spectrometry/RH5WBHJ2">mass spectrometer</a> can be removed during post-measurement <a href="/facts/Data_processing/74EKCDAq">data processing</a>. Without isotope references, measurements by mass spectrometry would be much less <a href="/facts/Accuracy_and_precision/JQ47xXDq">accurate</a> and could not be used in comparisons across different analytical facilities. 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 <a href="/facts/Peer_review/ly6yEgcW">peer-reviewed</a> scientific literature.
Isotope reference materials are generated, maintained, and sold by the International Atomic Energy Agency (<a href="/facts/International_Atomic_Energy_Agency/o84JrwQ7">IAEA</a>), the National Institute of Standards and Technology (<a href="/facts/National_Institute_of_Standards_and_Technology/gr9Fnh85">NIST</a>), the United States Geologic Survey (<a href="/facts/United_States_Geological_Survey/nVaGtMjl">USGS</a>), the Institute for Reference Materials and Measurements (<a href="/facts/Institute_for_Reference_Materials_and_Measurements/ChsCIgPq">IRMM</a>), and a variety of <a href="/facts/University/skaJt2Io">universities</a> and scientific supply companies. Each of the major stable isotope systems (<a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, <a href="/facts/Carbon/ukrgQexo">carbon</a>, <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a>, and <a href="/facts/Sulfur/IK0amTfM">sulfur</a>) has a wide variety of references encompassing distinct molecular structures. For example, <a href="/facts/Nitrogen/Nf1QpGDz">nitrogen</a> isotope reference materials include N-bearing molecules such <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> (NH3), atmospheric <a href="/facts/Dinitrogen/Nf1QpGDz">dinitrogen</a> (N2), and <a href="/facts/Nitrate/5AnVlYnL">nitrate</a> (NO3−). Isotopic abundances are commonly reported using the δ notation, which is the ratio of two isotopes (R) in a sample relative to the same ratio in a reference material, often reported in <a href="/facts/Per_mille/3xNDvE9l">per mille</a> (‰) (equation below). Reference material span a wide range of <a href="/facts/Isotopic_enrichment/07rvF6NA">isotopic</a> compositions, including enrichments (positive δ) and depletions (negative δ). While the <a href="/facts/Delta_(letter)/otPsSYj6">δ</a> values of references are widely available, estimates of the absolute isotope ratios (R) in these materials are seldom reported. This article aggregates the δ and R values of common and non-traditional stable isotope reference materials.

 
 
 
 
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 {\displaystyle \delta ^{X}={\frac {^{x/y}R_{sample}}{^{x/y}R_{reference}}}-1}

Reference materials for stable isotope analysis open-in-new

Reference materials for stable isotope analysis