Isotope reference materials

In IRMS, the measurement of isotope ratios requires the samples to be measured relative to a reference of a known isotope ratio. This is the only means to achieve the required precision level of 1.5 ppm, for example, the isotope ratio. 

Oceans contain almost 97% of the water on Earth and have a uniform isotope distribution. Oceans are the major sink in the hydrological cycle. The Standard Mean Ocean Water (SMOW) standard was initially proposed by Craig 1961 as a 

Pee Dee Belemnite is CaCOg of the rostrum of a bellemnite (Belemnita ameri-cana) from the Pee Dee Formation of South Carolina, USA. The PDB reference material has been exhausted for a long time. The new VPDB reference material was anchored by the IAEA with a fixed 5 value so that it corresponds nominally to the previous PDB scale. 

Nitrogen in atmospheric air has a very homogeneous isotope composition. The atmosphere is the main nitrogen sink and the largest terrestrial nitrogen reservoir. NSVEC is the reference material initially prepared by Jung and Svec, Iowa State 

The available IAEA reference materials are intended to calibrate local laboratory standards and not for continuous quality control purposes (Groening, 2004). Every laboratory should prepare for routine work, longlasting laboratory specific standards with similar characteristics to the used references and the working standards, which are calibrated against the primary reference materials. 

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For biochemical and medical applications, the International Atomic Energy Agency (IAEA) has issued a variety of stable isotope reference materials (Parr and Glements 1991) containing elevated levels of H, and 0. They are aU... 

Another major supplier of stable isotope reference materials is the Institute for Reference Materials and Measurements (IRMM) in Geel, Belgium. These materials... 

All values of the IRMM Isotopic Reference Materials are traceable to the SI (the international system of base quantities and base units). Isotopic measurement results corrected by means of these Isotope Ratio Reference Materials have reduced (ISO/BIPM) uncertainties. Isotopic measruements carried out against these Spike Reference Materials are traceable to the SI, if carried out properly. Further details are available from IRMM website see Chapter 8. 

Pare RM, Clements SA (1991) Intercomparison of enriched stable isotope reference materials for medical and biological studies. NAHRES-5, IAEA, Vienna. 

Raptis K, Mayer K, Hendrickx F, De Bievre P (1998) Preparation and certification of new thorium isotopic reference materials. Fresenius J Anal Chem 361 400-403 Rehkamper M, Halliday AN (1999) The precise measurement of T1 isotopic compositions by MC-ICP-MS Application to the analysis of geological materials and meteorites. Geochim Cosmochim Acta 63 935-944... 

Schimmelmann, A. (2007) H, C, N, O stable isotope reference materials from Indiana University. http //php.indiana.edu/ aschimme/hc.html. 

TABLE 4.3 Carbon Isotopic Composition of Selected Carbon-bearing Isotopic Reference Materials (Coplen et al., 2001)... 

Verkouteren, R. M. and Kleindienst, D. B. Value assignment and uncertainty estimation of selected light stable isotope reference materials. NIST Special Publication 260-149 (2004). 

Qi HP, Taylor PDP, Berglund M, DeBievre P (1997b) Calibrated measurements of the isotopic composition and atomic weight of the natural Li isotopic reference material IRMM-016. Int J Mass Sped Ion Proc 171 263-268... 

NIST SRM-979 is a high purity Cr(N03)3 9H20 crystalline sohd sold as an isotopic reference material. It was prepared from a commercial material and its isotopic composition was analyzed by TIMS, along with gravimetric mixtures of purified isotopes to examine instrumental bias (Sheilds et al. 1966). The absolute ratio is reported as 0.11339, with... 

SRM 979), Ni (nickel metal isotopic standard NIST SRM 986), Rb (rubidium chloride isotopic standard NIST SRM 984) and Sr (strontium carbonate isotopic standard NIST SRM 987). In addition, isotope reference materials are available for heavy elements such as T1 (thallium metal isotopic standard NIST SRM 997), Pb (NIST lead standard reference materials SRM 981-983) or U (uranium oxide NIST isotope standard U 005, U020, U350, U500 or U930) and others. The most important isotope standard reference materials applied in inorganic mass spectrometry are summarized in the table in Appendix V.17... 

Whereas TIMS suffers from the difficulties of time dependent mass fractionation in MC-ICP-MS, the mass fractionation is relatively constant. Its magnitude is often greater than that of TIMS and matrix effects are possible84. It is known that isotopic reference materials used for the calibration of isotope ratio measurements are available only as a pure metal or compound. Possible matrix effects during isotope ratio measurements, especially in solid-state... 

Re-assessment of silicon isotope reference materials (IRMM-018 and NBS 28 isotope standard) has been performed using both high resolution multiple ion collector ICP-MS and gas mass spec-... 

J. P. Snell, C. R. Quetel, L. Lamhertson, J. Qvamstrom, Preparation and certiPcation of ERM-AE670, a 202Hg enriched methylmercury isotopic reference material J. Anal. Atom. Spectrom., 19 (2004), 1315D1324. 

In 2005, De Laeter discussed the role of isotope reference materials for the analysis of non-traditionaT stable isotopes. At present, no isotopically certified reference materials exist for a large number of elements, including Cu, Zn, Mo and Cd, and it is important that this situation be rectified as soon as practicable. Before the isotopically certified reference materials become available for selected elements, suitable reference materials can be created as a standard if sufficient and reliable isotope data have been obtained by interlaboratory comparisons. For example, the Hf/ Hf isotope ratio was measured using hafnium oxide from Johnson Matthey Chemicals, JMC-475, for hafnium isotope ratio measurements with different multi-collector mass spectrometers (ICP-MS and TIMS) as summarized in Table 8.1. However, no isotope SRM is certified for the element Mo either. Mo isotope analysis is relevant, for example, for studying the isotope fractionation of molybdenum during chemical processes or the isotope variation of molybdenum in nature as the result of the predicted double (3 decay of Zr or 18.26-28 spectroscopically pure sample from Johnson Mattey Specpure is proposed as a laboratory standard reference material if sufficient and reliable isotope data are collected via an interlaboratory comparison. 

Mass spectrometer precision was determined by making repeated measurements on a gas sample prepared by combustion of carbon isotope reference material NBS-22. The standard deviation of the mean derived from 10 consecutive measurements of this gas was 0.02 %o The error associated with the combustion and purification procedure was measured by replicate combustions of the NBS-22 reference material, which resulted in a standard deviation of 0 12 %o for five samples ITius, the overall precision associated with the mass spectrometric measurement of vs PDB was 0.12 %o, or in absolute terms, 1.3 ppm. Most of the error clearly was associated with the combustion and sample handling process. Since sealed-tube combustions have been shown to produce theoretical recoveries of carbon (33). these small errors most likely arise from handling the CO2 after it is released from the sample tube ... 

Materials that can be used in analytical laboratories working in the fields of nuclear technology and isotope hydrology. These include uranium ore reference materials and other substances relevant to nuclear fuel technology as well as stable isotope reference materials for mass spectrometric determination of isotope ratios in natural waters. 

T. Ding, S. Valkiers, H. Kipphardt, R. De Bievre, RD.R Taylor, R. Gonfiantini, R. Krouse (2001) Calibrated sulfur isotope abundance ratios of three IAEA sulfur isotope reference materials and V-CDT with a reassessment of the atomic weight of sulfur. Geochim. Cosmochim. Acta 65, 2433-2437... 

Recommended uranium and plutonium isotopic reference materials for the determination of mass discrimination in isotopic analyses... 

Guidelines for selecting laboratory standards and a review of a strategy to have common referencing procedures between laboratories for isotopic measurements have been reported [4], Stable isotope reference materials (whether they be certified/primary standards or laboratory standards) should comply with a number of criteria. These criteria include ... 

Grdning, M. (2004) International stable isotope reference materials. In Handbook of Stable Isotope Analytical Techniques, Vol. 1, edited by de Groot, PA. Amsterdam, The Netherlands Elsevier, pp. 874-906. 

Figure 3.5 Use of three-isotope plots to check for spectral interferences in MC-ICP-MS. Each point represents the mean of an isotope ratio measurement of a standard (filled circles) or a sample (empty circle) of natural isotopic composition. Isotope ratios are plotted on the delta scale (5) as relative deviations in parts per thousand from the known isotope ratio of an isotopic reference material of natural isotopic composition. The diagonal line represents the theoretical fractionation curve as defined by the isotopic masses and an exponential fractionation law. (a) Absence of isobaric interferences. Data points from standard and sample plot on the theoretical curve, (b) At least one isotopic signal in the mass spectrum of the standard and the sample is subject to spectral interference from an isobaric nuclide, polyatomic ion, or doubly charged ion. (c) Matrix differences between sample and standard result in an offset of the sample data points from the theoretical fractionation curve.

NIST SRM 915a CaC03 isotopic reference material. The data are in good agreement with mass fractionation and there is no evidence of spectral interferences from isobaric nuclides, polyatomic ions, and/or doubly chained ions affecting the results. The variability is the result of the drift in the extent of instrumental mass discrimination exhibited by the MC-ICP-MS instrument used. Reproduced from [14],... 

In all these applications, isotope ratio data are produced, which are interpreted on an absolute or relative basis and which have an impact on our daily life, whether this is in science (e.g., age of an artifact), in society (e.g., provenance of food), or in public safety (e.g., neutron shielding in nuclear power plants). To ensure that these data are reliable and accurate, some specific requirements have to be fulfilled. The main requirement is that all these measurement results are comparable, which means that the corresponding results can be compared and differences between the measurement results can be used to draw further conclusions. This is only possible if the measurement results are traceable to the same reference [25]. This in turn can only be realized by applying isotopic reference materials (IRMs) for correction for bias and for validation of the analytical procedure. Whereas in earlier days only experts in mass spectrometry were able to deliver reproducible isotope ratio data, nowadays many laboratories, some of which may even have never been involved with mass spectrometry before, produce isotope ratio data using inductively coupled plasma mass spectrometry (ICP-MS). Especially for such users, IRMs are indispensable to permit proper method validation and reliable results. The rapid development and the broad availability of ICP-MS instrumentation have also led to an expansion of the research area and new elements are under investigation for their isotopic variations. In this context, all users require IRMs to correct for instrumental mass discrimination or at least to allow isotope ratio data to be related to a commonly accepted basis. 

Definition RM certified for the isotopic composition of a specific element or compound contained in the isotopic reference material (IRM). 

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