Isotopic standards

MS", application of successive mass spectrometric measurements n of them), particularly in linked scanning of m/z, which is the ratio of the mass (m) of an ion and the number of charges (z) on it. Older publications used m/e, but as e is the actual charge on an electron and not the number of charges on the ion, the use of m/e was abandoned, m/z. mass-to-charge ratio, a measure of molecular mass PDB. PeeDee Belemnite (a carbon isotope standard see VPDB)... 

VPDB. Vienna PeeDee Belemnite (a replacement for the PDB isotope standard)... 

Craig, H. (1957a). Isotopic standards for carbon and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim. Cosmochim. Acta 12, 133-149. 

Miller, K.G., Feigenson, M.D. and Wright, J.D. (1991) Miocene isotope standard section, DSDP Site 608 An evaluation of isotope and biostratigraphic resolution. Paleoceanography, 6, 33-52. 

Table 9.1 A selection from the Table of Light Stable Isotope Standard Reference Materials avail-...

Example A potential drug and its metabolite in a liver sample are quantified by internal standardization with trideuterated standards for both compounds (Fig. 12.4). [25] Under these conditions it neither presents a problem that both analytes and their isotopic standards are almost co-eluting from the LC column, nor does the completely unspecific TIC play a role. If required for sensitivity reasons, this analysis could also have been performed in the SIM mode using the m/z values of the RICs shown. 

Table 2.5 5 0-values of commonly used O-isotope standards... 

Table 2.5 gives the 5 0-valnes of commonly used oxygen isotope standards on both scales (parenthesis denote calcnlated values). 

Although internal correction does not need any external isotopic standards, the correction requires that the element has at least two natural non-radiogenic isotopes. Some elements, e.g., Nd and Sr, satisfy this requirement. Take Sr and Nd internal linear correction as examples. 

For the best results, such a correction should be applied to each individual isotopic pair that is to be ratioed, although this is not always possible in practice since a large number of isotopic standards would be needed to cover every eventuality. 

A direct result of the ability to measure isotope ratios with ICP-MS is the technique known as isotope dilution analysis. This is done by spiking the sample to be analysed with a known concentration of an enriched isotopic standard, and the isotope ratio is measured by mass spectrometry. The observed isotope ratio (RJ of the two chosen isotopes can then be used in the isotope dilution equation (Eqn. 5.7) to calculate the concentration of the element in the sample ... 

Enriched cadmium isotopic standard (Spectrascan Stable Isotope Solution, Teknolab A/S, P.O. Box 131, N-1441 Drobak, Norway). 

A single measurement of a calibration sample can give the concentration of the test solution by a simple ratio. This is often done in techniques where a calibration internal standard can be measured simultaneously (within one spectrum or chromatogram) with the analyte and the system is sufficiently well behaved for the proportionality to be maintained. Examples are in quantitative nuclear magnetic resonance with an internal proton standard added to the test solution, or in isotope dilution mass spectrometry where an isotope standard gives the reference signal. For instrument responses As and /sample for internal standard and sample, respectively, and if the concentration of the internal standard is Cjs, then... 

One problem is the availability of reliable reference materials for isotope ratio measurements. Certified isotope standard reference materials are available from NIST (National Institute of Standard Reference Materials, http //www.nist.gov/srd/, formerly NBS - National Bureau of Standards) and IRMM (Institute for Reference Materials and Measurements, http //www.irmm.jrc.de). There are isotope standard reference materials for light elements (H, Li, , C, N, O), Mg (magnesium metal isotopic standard NIST SRM 980), and for moderately heavy elements such as (potassium chloride isotopic standard NIST SRM 985), Cr (chromium metal isotopic standard NIST... 

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... 

An analytical procedure has been proposed for precise uranium isotope ratio measurements in a thin uranium layer on a biological surface by LA-ICP-MS using a cooled laser ablation chamber.125 One drop of uranium isotope standard reference materials NIST, 350, NIST 930, of our isotopic laboratory standard CCLU 500 (20p.l, U concentration 200 ng 1) and of uranium with natural isotopic pattern were deposited on the leaf surface and analyzed by LA-ICP-MS at well defined laser crater diameters of 10, 15, 25 and 50 p.m. A precision for measurements of isotope ratios in the range of 2.1-1.0% for 235U/238U in selected isotope standards was observed whereby the precision and the accuracy of isotope ratios compared to the non-cooled laser ablation chamber was improved.125... 

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-... 

Van den Boom et al.150 have reported on the determination of silicon isotope ratio measurements in silicate materials by MC-ICP-MS (at a mass resolution of 2500 to resolve isobaric interferences) after sodium hydroxide sample digestion and purification of silicon. 829Si and 830Si have been determined for several silicon isotope standard reference materials. A precision for 830Si of 0.18-0.41 %o was achieved. Precise and accurate measurements of isotope ratios on transient signals by HPLC-MC-ICP-MS for nuclear application was performed by Giinther-Leopold et al.151... 

The isotope variation of boron isotopic composition in aqueous fluids in environments on the Earth s surface has been reviewed by You.185 The boron isotope composition (8nB) is expressed as a per mil (%o) deviation from the boron isotope standard NIST SRM 951 ... 

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