Isotope abundance, measurements

The earlier stable isotope dilution mass spectrographic work was accomplished with a thermal ion mass spectrometer which had been specifically designed for isotope abundance measurements. However, Leipziger [829] demonstrated that the spark source mass spectrometer could also be used satisfactorily for this purpose. Although it did not possess the excellent precision of the thermal unit, Paulsen and coworkers [830] pointed out that it did have a number of important advantages. 

A. O. Nier. A Mass Spectrometer for Routine Isotope Abundance Measurements. Rev. Sci. Instrum., 11(1940) 212-216. 

Natural products such as wine, fruit juices, flavors, oils, and honey are prime targets for fraudulent adulteration because of their high prices. Sophisticated analytical methods (perhaps including isotope abundance measurements) are required to detect whether natural ingredients have been mixed with ones from cheaper synthetic sources. Isotope abundance is markedly different for natural vs. synthetic molecules and these differences can be exploited to detect adulteration. Several examples follow. 

In Inductively Coupled Plasma Mass Spectrometry. Montaser A (ed) Wiley-VCH, New York, p 83-264 Montaser A, Zhang H (1998) Mass spectrometry with mixed-gas and Helium ICPS. In Inductively Coupled Plasma Mass Spectrometry. Montaser A (ed), Wiley-VCH, New York, p 809-890 Nier AO (1940) A mass spectrometer for routine isotope abundances measurement. Rev Sci Instrum 11 212-216... 

Fletcher IR, Maggi AL, Rosman KJR, McNaughton NJ (1997b) Isotopic abundance measurements of K and Ca using a wide-dispersion multi-collector mass spectrometer and low-fractionation ionisation techniques. Int J Mass Spectrom Ion Proc 163(1-2) 1-17... 

McMullen, C.C. Thode, H.G. Isotope Abundance Measurements and Their Application to Chemistry, In "Mass Spectrometry , McDowell, C.D., Ed., McGraw-Hill New York, 1963. 

This section provides a brief guide to biological applications of stable isotopes and to isotopic abundance measurement using mass spectrometry. 

Elements other than Pb have been measured by TIMS in polar snow (43, 49, 50, 53), showing the high potential of the technique. Bismuth determination (43) is characterized an accuracy comparable to that of LEAFS and takes advantage of the simultaneous ionisation of Bi and Pb during the Pb isotopic abundance measurements. Determination of Ba was also carried out on some Antarctic samples (53) showing its possible use as a reference element in monitoring the contribution of terrestrial dust level. 

Following the pioneer work of Aston and Dempster, there were rather limited advances made in the field of isotopic abundance measurements until 1935 when A. 0. Nier (85) introduced a number of improvements to mass spectrometer design. Since then, many more refinements have been made, particularly with regard to more efficient ion sources and to more sensitive ion detectors, so much so, that the mass spectrometer has become an extremely sensitive instrument for the detection of practically all of the elements, and its sensitivity remains second only to that of radioactive counting techniques. 

Sources of error in isotope abundance measurements have been discussed in detail elsewhere (106). The reproducibility of results with a modern instrument is usually better than 0.1%. Furthermore, it is possible to detect differences in isotope ratios of better than 0.02% using isotope ratio instruments which employ simultaneous ion collection systems. These high-precision isotope ratio instruments are used extensively to study equilibrium and kinetic isotope effects in chemistry and to measure the variations in isotope abundances that occur in nature. 

It was clear from the time of the first fission product studies that the mass spectrometer would eventually be used in separation problems, mass identification, and isotope abundance measurements. However, the early work on fission products involved very small samples of material and only radiochemical methods were considered sensitive enough to identify and follow the radioactive isotopes. In 1945, Thode and Graham (104) succeeded in obtaining mass spectrograms of the xenon and krypton isotopes formed in the thermal neutron fission of U23B. 

The mass spectrometric method of fission product yield measurements can be applied to the entire mass range of fission products. Inghram et al. (55) investigated fission products in the rare earth region and showed how the partial yield curves obtained from isotope abundance measurements for the various elements can be fitted together by the method of stable... 

One important feature of the mass spectrometric method of fission yield determinations is the ease with which a large number of mass chains may be investigated at the same time for a mixture of fission products from a single irradiation, Since ions for the various elements are emitted from a sample on a hot filament at different temperatures, isotope abundance measurements of a number of elements may be made on a single sample without chemical separation. It is, therefore, possible to obtain a large body of yield data for a particular fission process with high relative accuracy ( 1%). 

Y. Xu, J.-F. Heilier, G. Madallnski, E. Genin, E. Ezan, J.-C. Tabet, and C. ]unot. Evaluation of accurate mass and relative isotopic abundance measurements in the LTQ-Orbitrap mass spectrometer for further metabolomics database building. Anal. Chem., 82 5490-5501,2010. 

Dietz, L.A., Pachucki, C.F., and Land, G.A. (1962) Internal standard technique for precise isotopic abundance measurements in thermal ionization mass spectrometry. Anal. Chem., 34, 709-710. 

Nier, A. O. 1940. A mass spectrometer for rontine isotope abundance measurements. Rev. Sci. Inst. 11 212—6. 

Elemental identification and isotopic abundance measurement of both short-lived and stable species in physics and radiochemistry (nuclear waste), in geochemistry and more recently in the life sciences. 

Analytical Considerations for Isotope Abundance Measurements (Table 3)... 

The variation in isotope abundance measurement in GC-C-IRMS and GC-P-IRMS is much less than in GC-MS. Therefore, molar enrichments of 0.01% can still be quantified. For this reason, IRMS techniques can replace MS techniques at low enrichment levels or can be added to the MS technique in order to extend an isotopic decay curve to enable multicompartment analysis. However, the latter application may be unnecessary since linearity of GC-C-IRMS is usually excellent. Linearity has been shown from 0.01 to 25% molar enrichment for valine... 

Standards The standard for carbon isotope abundance measurements is based on a Cretaceous belem-nite sample from the Peedee formation in South Carolina, USA. The original material is no longer available. It has been replaced by the convention that NBS 19, a carbonate material, has a value of -i-1.95 l versus PDB. This new scale is termed V-PDB (Vienna-PDB). The IAEA distributes a number of secondary standards including graphite (USGS24) with a d C value of - 15.994 V-PDB, oil (NBS-22) at -29.741 V-PDB, and calcium carbonate (NBS-18) with a value of - 5.014 V-PDB. 

Benech, H., Batel, A., Rruvost, A., Thomas, J.-L., and Grognet, J.-M. (1998) Magnesium isotopic abundance measurement in humans comparison of two mass spectrometric methods. Magnes. Res., 11,91-102. 

C. C. McMullen and H. G. Thode, Isotope abundance measurements and their application to chemistry, in Mass Spectrometry (A. McDowell, ed.), pp. 375-441, McGraw-Hill, New York (1963). 

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