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Fractionation of isotopes

Earlier in this chapter, we discussed isotopic fractionation during evaporation. Under appropriate conditions, where the condensed phase remains isotopically well mixed and the gas phase is removed from the system to prevent back reaction, Rayleigh distillation will occur (Box 7.2), resulting in a condensed phase that is isotopically heavy relative to the starting composition (Fig. 7.9). Isotopic fractionation can occur during both condensation and evaporation, as demonstrated by experiments (Richter el al., 2002). But it is not necessary that isotopes fractionate during evaporation or condensation. It depends on the details of the process. If evaporation occurs into a gas phase that is sufficiently dense, back reactions between gas and liquid can reduce the isotopic fractionation to near the equilibrium value, which is very small. For example, sulfur in chondrules does not show the isotopic fractionation (Tachibana and Huss, 2005) expected during evaporation from a liquid. Also, evaporation from a solid does not produce isotopic fractionation in the solid because diffusion is much too slow to equilibrate the few layers of surface atoms that are fractionated with the bulk of the material. [Pg.220]

The degree of equilibrium isotopic fractionation among phases depends on temperature, so the isotopic compositions of co-existing phases can be used for thermometry. Oxygen is widely used in this way. For example, Clayton and Mayeda (1984) found that the oxygen isotopic compositions of calcite and phyllosilicates from Murchison lie on a mass-dependent fractionation line and differ in 6180 by 22%o. This difference requires a temperature of around 0 °C, which is interpreted to be the temperature of aqueous alteration on the Murchison parent asteroid. Similar measurements for Cl chondrites indicate that aqueous alteration for these meteorites occurred at higher temperature, 50-150 °C (Clayton and Mayeda, 1999). [Pg.221]


One of the most significant sources of change in isotope ratios is caused by the small mass differences between isotopes and their effects on the physical properties of elements and compounds. For example, ordinary water (mostly Ej O) has a lower density, lower boiling point, and higher vapor pressure than does heavy water (mostly H2 0). Other major changes can occur through exchange processes. Such physical and kinetic differences lead to natural local fractionation of isotopes. Artificial fractionation (enrichment or depletion) of uranium isotopes is the basis for construction of atomic bombs, nuclear power reactors, and depleted uranium weapons. [Pg.353]

Special sample inlet devices such as nebulizers, furnaces, and gas inlets are commonly used to avoid cross-contamination and accidental fractionation of isotopes. [Pg.426]

Galimov EM (1985) The biological fractionation of isotopes. Academic Press, Orlando... [Pg.424]

Galimov, E.M. The Biological Fractionation of Isotopes, Academic, New York, 1985. [Pg.312]

A more general expression for the equilibrium fractionation of isotopes X and " yX, applicable to all diatomic and larger molecules is ... [Pg.74]

The data described above demonstrate a substantial fractionation of isotopes for both Cu and Zn. Zinc isotopic variability is particularly noticeable in the marine environment the 8 Zn... [Pg.420]

There are three models for mass fractionation of isotopes in the ionization processes a linear law, a power law and an exponential law (Wasserburg et al., 1981 Lee et al., 2001). [Pg.208]

In some of the experimental work on this system a mercury resonance lamp made with isotope 202 has been used. Mercury with the usual isotopic distribution was mixed with the methyl chloride. Let X1 be the atomic fraction of isotope 202 in the HgCl formed and X1 be the atomic fraction of isotope 202 in ordinary mercury. Then... [Pg.17]

The fractionation of isotopes between different phases is of primary concern to geochemists. For two different phases A and B, the fractionation factor (oca-b) is defined as (isotope ratio in A) / (isotope ratio in B) and can be related to 8 values by equation 3.13. [Pg.125]

Regnier, F. E. (2001). Fractionation of isotopically labeled peptides in quantitative proteomics. Anal. Chem. 73, 5142-5149. [Pg.88]

X]/Xo,i) represents the fraction of isotope 1 remaining in the gas, which in most cases will be a very good approximation to the fraction of element k remaining in the gas. The isotopic composition of the condensate as a function of the fraction of gas remaining is given by... [Pg.412]

Kaplan, I.R. and Rittenberg, S.C., 1962. Fractionation of isotopes in relation to the problem of elemental sulfur transport by microorganisms. Nature, 194 1098—1099. [Pg.396]

At equilibrium, the activity ratio between any two members of a decay series is 1.00. However, at and near the Earth s surface, disequilibrium of the various nuclides of the uranium series is found to occur. The disequilibrium is especially pronounced in groundwaters (Cherdyntsev, 1971 Osmond and Cowart, 1976). The fractionation of the nuclides can occur as a result of chemical differences between elements, the fractionation of isotopes of a given element may occur because of preferential leaching of one (because of its radiogenic origin), or by the direct action of recoil during radioactive decay (Osmond and Cowart, 1976). [Pg.186]

Mass spectrometric analysis of isotope ratios is in principle very accurate (isotope ratio mass spectrometers were developed for geochemical investigations), but the analytical problem comes from possible fractionation of isotopes in the workup procedure. Traditionally, isotope ratio mass spectrometry measurements of kinetic isotope effects have been confined to reactions which give a small molecule product (such as CO2), which can be directly introduced to the mass spectrometer. [Pg.101]

Fractionation of isotopes or impurities dictate the use of boiling points (vanishingly small vapor fractions) for hydrogen and neon and condensation point (vanishingly small liquid fraction) for oxygen. [Pg.283]

The equilibrium fractionation of isotopes between substances is analogous in many ways to the partitioning of cations (such as Fe and Mg) between minerals. Both processes can be described in terms of chemical reactions in which isotopes or cations are exchanged between two coexisting phases. For example, the partitioning of Fe and Mg between orthopyroxene and olivine can be described by the reaction ... [Pg.2]

In terms of the fraction of isotopic exchange, F, this expression can be cast as... [Pg.102]


See other pages where Fractionation of isotopes is mentioned: [Pg.353]    [Pg.302]    [Pg.18]    [Pg.241]    [Pg.726]    [Pg.244]    [Pg.350]    [Pg.134]    [Pg.134]    [Pg.178]    [Pg.392]    [Pg.122]    [Pg.210]    [Pg.220]    [Pg.122]    [Pg.343]    [Pg.21]    [Pg.500]    [Pg.209]    [Pg.412]    [Pg.353]    [Pg.1315]    [Pg.9]    [Pg.53]    [Pg.85]    [Pg.102]   
See also in sourсe #XX -- [ Pg.74 , Pg.84 , Pg.90 , Pg.92 , Pg.177 ]

See also in sourсe #XX -- [ Pg.139 ]




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