Stable isotopes measuring abundances

Fluorine is the 24th most abundant element in the universe, just after zinc and before copper. Because F has but a single stable isotope, stellar abundance observations measure 19F, the 46th most abundant isotope, which has... 

The increasing availabihty of mass spectrometers and on-Hne interfaces for sample preparation has made natural abundance measurements accessible to a broad community of biological oceanographers, and stable isotope measurements are becoming a routine tool in studies of marine ecosystems. In general, measurements are now carried out with continuous flow systems that integrate a... 

T. Preston (1992) The measurement of stable isotope natural abundance variations. Plant Cell Environ. 15, 1091-1097... 

In particular cases it is necessary to determine the origins or fate of oxygen in biosynthesis. For this only the stable isotope (natural abundance 0.2%) is available and it is analysed for by mass spectrometry, a single label giving rise to M + 2 peaks which are measured with comparative sensitivity. The stable... 

For marble provenance studies, the most successful technique seems to be the measurement, through mass spectrometry, of the abundance ratios of the stable isotopes of carbon and oxygen (116). However, no single technique appears to provide unequivocal results, especially in cases such as the different Mediterranean sources, and a combination is often necessary to arrive at an approximate place of origin (117). 

Abundances of lUPAC (the International Union of Pure and Applied Chemistry). Their most recent recommendations are tabulated on the inside front fly sheet. From this it is clear that there is still a wide variation in the reliability of the data. The most accurately quoted value is that for fluorine which is known to better than I part in 38 million the least accurate is for boron (1 part in 1500, i.e. 7 parts in [O ). Apart from boron all values are reliable to better than 5 parts in [O and the majority arc reliable to better than I part in 10. For some elements (such as boron) the rather large uncertainty arises not because of experimental error, since the use of mass-spcctrometric measurements has yielded results of very high precision, but because the natural variation in the relative abundance of the 2 isotopes °B and "B results in a range of values of at least 0.003 about the quoted value of 10.811. By contrast, there is no known variation in isotopic abundances for elements such as selenium and osmium, but calibrated mass-spcctrometric data are not available, and the existence of 6 and 7 stable isotopes respectively for these elements makes high precision difficult to obtain they are thus prime candidates for improvement. 

Stott, A.W., Davies, E., Evershed, R.E. and Tuross, N. 1997 Monitoring the routing of dietary and biosynthesized lipids through compound-specific stable isotope (delta C) measurements at natural abundance. Naturwissenschcften 84(2) 82-86. 

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. 

The thermal ion mass spectrometer was specifically developed for the measurement of isotope abundances and is capable of excellent precision. Although the spark source mass spectrometer used in this work lacks some of this precision, it has proved very useful in stable isotope dilution work. It has a number of advantages, including greater versatility, relatively uniform sensitivity, and better applicability to a wide range of elements. 

In radiocarbon dating, the quantity to be measured is the ratio of the abundances of the rare isotope (14C) to that of the stable isotopes (12C, 13C). These abundance ratios are not measured on an absolute basis, but are compared to that of an internationally-accepted standard. (It is likely that a similar standard will be adopted for 10Be dating.) These measurement requirements have several consequences ... 

If the stable isotope ratio of 13C/12C is to be further measured in tree rings and interpreted as an indicator of climate variation, (and we have barely begun to initiate its use as a thermometer in the present work, confining our measurements to the stable isotopes in water, because water is so abundant compared to carbon dioxide and because the dependence of its isotope ratios is relatively simple compared with those of carbon dioxide), some more sophisticated considerations must be given to the distribution of carbon dioxide among the reservoirs on the surface of the earth. 

Mass spectrometry is one of the oldest instrumental analytical methods. Positive rays were discovered by Goldstein in 1886 (after Barrie Prosser, 2000). The first mass spectrometer for routine measurements of stable isotope abundances was reported in 1940 and improved upon over the following ten years Nier, 1940, Nier, 1947, Murphey, 1947, McKinney et al, 1950, after Prosser, 1993. It is remarkable that the vast majority of active gas spectrometers in use today are little changed from those described around 50 years ago. For most people, mass spectrometry now means organic molecular structure determination. However, within the last 15... 

The elements whose isotopes are routinely measured with gas inlet mass spectrometers are carbon (12C and 13C, but not 14C), oxygen (160, 170, l80), hydrogen ( H, 2H, but not 3H), nitrogen (14N and 1SN) and sulphur (32S, 33S, 34). Stable isotopes of H, C, N, O, and S occur naturally throughout atmosphere, hydrosphere, lithosphere, and biosphere. They are atoms of the same elements with a different mass. Each element has a dominant light isotope with the nominal atomic weight (I2C, 160,14N, 32S, and H) and one or two heavy isotopes (l3C, nO, 180, 15N, 33S, 34S, and, 2H) with a natural abundance of a few percent or less Table 1). 

Stable-isotope dilution analysis is an analytical technique in which a known quantity of a stable-labelled isotope is added to a sample prior to extraction, in order to quantitate a particular compound. The ratio of the naturally abundant and the stable-labelled isotope is a measure of the naturally abundant compound and can be determined only by gas chromatography-mass spectrometry since the naturally abundant and the stable-labelled isotope cannot be completely separated gas chromatographically. 

Because the natural variations in stable isotope abundances are usually very small (see above), and since routine measurements are usually made in an isotope ratio mass spectrometer which compares the relative intensities of the mass resolved beams of the sample with those of some standard material (Section 7.2.2), it is standard practice to report abundance ratios using the dimensionless 8-value notation. 

This was the first extinct radioactivity detected (Jeffrey and Reynolds 1961) and was made possible by the early high sensitivity of rare gas measurements and the low abrmdance of Xe in rocks. I has only one stable isotope at mass 127. Its abundance is measured as Xe after exposing a sample to an adequate neutron flux. The correlation between Xe and Xe observed in a stepwise degassing of a sample demonstrates that the excess Xe results from decay (Fig. 9h). Results in primitive meteorites and inclusions show that i29j/i2tj j.jose to 10 . Chronometry with I- Xe has been widely used in meteorite work (Reynolds 1963 Hohenberg 1967) but occasionally has some diflflculties to agree with the other chronometers due to the sensitivity of I to secondary processes and water alteration (Pravdivtseva et al. 2003 Busfleld et al. 2004 see also Swindle and Podosek (1988) for an extensive review). ... 

Newton R, Aranovich L (1996) Simple granulite melting in concentrated NaCl-KCl solutions at deep crustal conditions. Geol Soc Am Annu Meet Abstracts with Programs 158 Numata M, Nakamura N, Koshikawa H, Terashima Y (2002) Chlorine isotope fractionation during reductive dechlorination of chlorinated ethenes by anaerobic bacteria. Env Sci Tech 36(20) 4389-4394 Numata M, Nakamura N, Gamo T (2001) Precise measurement of chlorine stable isotopic ratios by thermal ionization mass spectrometry. Geochem J 35(2) 89-100 Owen HR, Schaeffer OA (1995) The isotope abundances of chlorine from various sources. J Am Chem Soc 77 898-899... 

Mass spectrometer (1) A scientific instrument used to identify organic compounds. (1) A scientific instrument used to measure the relative abundance of stable isotopes in a sample, e.g. isotope ratio mass spectrometer (IRMS). 

In practice, because in radiometric determinations based on mass spectrometry it is more convenient to measure mass ratios than absolute values, equation 11.85 is usually rewritten as follows, normalized to the abundance of the stable isotope Sr ... 

The accuracy with which absolute isotope abundances can be measured is substantially poorer than the precision with which relative differences in isotope abundances between two samples can be determined. Nevertheless, the determination of absolute isotope ratios is very important, because these numbers form the basis for the calculation of the relative differences, the 5-values. Table 1.6 sununarizes absolute isotope ratios of primary standards used by the international stable isotope community. 

Brand W (2002) Mass spectrometer hardware for analyzing stable isotope ratios. In P de Groot (ed.) Handbook of stable isotope analytical techniques. Elsevier, Amsterdam Brandriss ME, O Neil JR, Edlund MB, Stoermer EF (1998) Oxygen isotope fractionation between diatomaceous silica and water. Geochim Cosmochim Acta 62 1119-1125 Bremner JM, Keeney DR (1966) Determination and isotope ratio analysis of different forms of nitrogen in soils. III. Soil Sci Soc Am Proc 30 577-582 Brenninkmeijer CAM (1993) Measurement of the abundance of CO in the atmosphere and the and 0/ 0 ratio of atmospheric CO with applications in New Zealand and Australia. J Geophys Res 98 10595-10614... 

A measure of the amount of a stable isotopic label that exceeds its natural abundance in unlabeled tracee. This is most directly accomplished using an ion ratio mass spectrometer to measure the ratio of ion currents for isotopomers such as C02 at mass 44 and 2 at mass 45. From the difference between the ion current ratio for a sample (Zsampie) and the ion current ratio for a reference gas (Zreference), the atom percent excess (APE) can be estimated. See Tracer/Tracee Ratio Compart-mental Analysis Isotope Exchange Kinetics... 

A quantitative measure of isotope composition relative to the abundance of all isotopic forms found in nature. Values for those stable isotopes most commonly employed in biological tracer experiments are H, 99.985% ... 

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