Isotope composition separation

Almost any type of analyzer could be used to separate isotopes, so their ratios of abundances can be measured. In practice, the type of analyzer employed will depend on the resolution needed to differentiate among a range of isotopes. When the isotopes are locked into multielement ions, it becomes difficult to separate all of the possible isotopes. For example, an ion of composition CgHijOj will actually consist of many compositions if all of the isotopes ( C, C, H, H, 0, O, and 0) are considered. To resolve all of these isotopic compositions before measurement of their abundances is difficult. For low-molecular-mass ions (HjO, COj) or for atomic ions (Ca, Cl), the problems are not so severe. Therefore, most accurate isotope ratio measurements are made on low-molecular-mass species, and resolution of these even with simple analyzers is not difficult. The most widely used analyzers are based on magnets, quadrupoles, ion traps, and time-of-flight instruments. 

Isotope dilution measurements using a and/or spike tracer can be performed separately, or combined with the isotopic composition run. Spike tracers can be measured on an ion counting channel, or alternatively, it may be preferable to concentrate the tracer (provided the spike corrections are small) and measure it on a... 

According to the model, this isotopic composition was fixed tm years ago (on the separation of the lead minerals from the uranium- and thorium-bearing environment), is unchanged to the present day and is therefore measurable. There are two similar equations for the other two radiogenic stable isotopes of lead. To simplify the manipulation, we can use the following notation ... 

In LC-ICP-MS, samples are separated on a chromatographic column, which may be a simple silica or alumina column with a relatively simple eluent. As the components elute from the column, they enter the ICP and the identity of the elements present and their concentration are determined based on the wavelengths of light (identity) and intensity of light (quantification) they emit. The exhaust from the ICP then enters the mass spectrometer, where the metals and their isotopic composition are determined based on their characteristic m/z ratios. The metals are thus identified and verified by two methods, ICP and MS [15]. 

Keesom, W. H. and van Dijr, H. On the possibility of separating neon and its isotopic components by rectification. Koninklijke Akademie van Wetenschappen te Amsterdam, Proc. of the Sect, of Sciences XXXIV, 42-50 (1931) Keesom, W. H. and Hantjes, Vapor pressures of neon of different isotopic compositions. J. Physica 2, 986-999 (1935). 

The protocol described in Section 7.1.2 involves isotopic competition, but with the different isotopomers held in separate containers. Equations 7.10 to 7.13 apply equally well to a type of competition experiment known in biochemistry as the perturbation method for determining KIE s of reversible enzyme catalyzed reactions. The perturbation method differs from simultaneous non-competitive measurements in several important ways. One begins by mixing equilibrium concentrations of substrate and product but with one component (substrate or product) at a different isotopic composition than the other. Thus, the mixture is in chemical, but not isotopic equilibrium. At this stage no enzyme is present and the interconversion is... 

In principle, the three isotope method may be widely applied to new isotope systems such as Mg, Ca, Cr, Fe, Zn, Se, and Mo. Unlike isotopic analysis of purified oxygen, however, isotopic analysis of metals that have been separated from complex matrices commonly involves measurement of several isotopic ratios to monitor potential isobars, evaluate the internal consistency of the data through comparison with mass-dependent fractionation relations (e.g., Eqn. 8 above), or use in double-spike corrections for instrumental mass bias (Chapter 4 Albarede and Beard 2004). For experimental data that reflect partial isotopic exchange, their isotopic compositions will not lie along a mass-dependent fractionation line, but will instead lie along a line at high angle to a mass-dependent relation (Fig. 10), which will limit the use of multiple isotopic ratios for isobar corrections, data quality checks, and double-spike corrections. 

Figure 8. Plot of Li isotopic composition vs. Na O content of eclogites from Trescolmen, Swiss Alps (Zack et al. 2003). Data from pairs of bulk rock ( ) and omphacite mineral separate (O) samples, indicating that bulk rocks generally preserve isotopic systematics of these rocks. Well-preserved, high pressure metamorphosed basaltic rocks were interpreted to retain much of their elemental character, and as such were good recorders of the residue remaining after subduction dehydration. The data indicated that originally isotopically heavy altered sea floor basalt could be transformed during subduction into some of the isotopically lightest materials in the Earth system.

Oi T, Odagiri T, Nomura M (1997) Extraction of lithium from GSJ rock reference samples and determination of their lithium isotopic compositions. Anal Chim Acta 340 221-225 Oi T, Shimizu K, Tayama S, Matsuno Y, Hosoe M (1999) Cubic antimonic acid as column-packing material for chromatographic lithium isotope separation. Sep Sci Tech 34 805-816 Olsher U, Izatt RM, Bradshaw JS, Dailey NK (1991) Coordination chemistry of lithium ion a crystal and molecular structure review. Chem Rev 91 137-164... 

Grustal reservoirs are also variable in Gl-isotope compositions (Figs. 1-6) due to fractionation of the Gl-isotope compositions inherited from their mantle source through fluid-mineral reactions, incorporation of G1 derived from the oceans and fractionation within fluid reservoirs by diffusion (see below). For example, the oceanic crust is enriched in Gl (and pore fluids depleted in Gl) through reaction of seawater with basaltic crust derived from the depleted mantle (Fig. 1 Magenheim et al. 1995). Undoubtedly, future investigations of Gl-isotopes in whole rocks and mineral separates will address the Gl-isotope compositions of these reservoirs and their evolution. 

Seawater and marine pore fluids. As discussed above, the chlorine isotopic composition of modem seawater does not vary measurably. This is not surprising in light of its long residence hme (approximately 90 million years) and its conservative behavior in the water column. In contrast, marine pore fluids have been demonstrated to vary considerably. There is also the likelihood that hydrothermal fluids may be fractionated as a result of exchange with mineral phases, as phase separation under marine hydrothermal conditions does not appear to lead to measurable fractionation (e.g., Magenheim et al. 1995). However, to date no stable-chlorine isotopic compositions of marine hydrothermal fluids have been reported in the literature. 

PCB isotopic compositions have been reported for mixtures produced by Monsanto (USA), Bayer (Germany), and Caffaro (Italy) (e.g., Reddy et al. 2000 Drenzek et al. 2002). The Monsanto mixtures (Arochlors) were supplied from three separate environmental standard suppliers. The 5 C1 values of all the samples fell within a limited range of-3.37 to -2.11%o. However, there were resolvable differences between the same Arochlor mixture supplied from different sources. A preliminary survey of contaminated sediments (e.g., Reddy et al. 2000) indicated that two samples which have PCBs that have been affected by alteration as evidenced by the lower amounts of less chlorinated congeners were isotopically distinct from the range of the source materials (assumed to be similar to the analyzed pure samples) while other samples were not distinguishable from the source material. 

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