Fractionation factor stable isotopes

One possibility for separating the contributions of primary sources with the same mass composition is to include stable isotope measurements. Isotope balances in addition to mass balances have been used with some success in areas where local sources dominate long-range transport effects(30). For isotope balances, fractionation factors cannot be considered unity. There is a fractionation effect between light and heavy isotopes for each physical-chemical change. For equilibrium between gas and liquid species and species of different oxidation states, the fractionation factors are fixed. 

Throughout this chapter, variations in isotopic compositions will be described using conventional stable isotope notation. Fractionation factors are defined in terms of alpha, with... 

Friedman I, O Neil JR (1977) Compilation of stable isotope fractionation factors of geochemical interest. U S Geol Surv Prof Paper 440-KK... 

Solving the forward problem of the isotopic and chemical evolution of n reservoir exchanging a radioactive and its daughter isotope requires the solution of 3n— 1 differential equations (the minus one stems from the closure condition). The parameters are n (n — 1) independent flux factors k for the stable isotope N and n (n — 1) independent M/N fractionation factors D. In addition, the n values of R y the n values of Rh and the n—1 allotments x of the stable isotope among the reservoirs must be assumed at some time, preferably at the beginning of the evolution (e.g., 4.5 Ga ago), or in the modern times, in which case integration is carried out backwards in time. 

Fortier SM, Cole DR, Wesolowski DJ, Riciputi LR, Paterson BA, Valley JW, Horita J (1995) Determination of the magnetite-water equilibrium oxygen isotope fractionation factor at 350°C a comparison of ion microprobe and laser fluorination techniques. Geochim Cosmochim Acta 59 3871-3875 Friedman I, O Neil JR (1977) Compilation of Stable Isotope Fractionation Factors of Geochemical Interest. US Geol Surv Prof Paper 440-KK... 

Fractionations are typically very small, on the order of parts per thousand or parts per ten thousand, so it is common to see expressions like 1000 ln(a) or 1000 (a-l) that magnify the difference between a and 1. a =1.001(1000 [a-l] = 1) is equivalent to a 1 per mil (%o) fractionation. Readers of the primary theoretical literature on stable isotope fractionations will frequently encounter results tabulated in terms of P-factors or equilibrium constants. For present purposes, we can think of Pjjh as simply a theoretical fractionation calculated between some substance JiR containing the elementX, and dissociated, non-interacting atoms ofX. In the present review the synonymous term Uxr-x is used. This type of fractionation factor is a convenient way to tabulate theoretical fractionations relative to a common exchange partner (dissociated, isolated atoms), and can easily be converted into fractionation factors for any exchange reaction ... 

Heterogeneities in stable isotopes are difficult to detect, because stable isotope ratios are affected by the various partial melting-crystal fractionation processes that are governed by temperature-dependent fractionation factors between residual crystals and partial melt and between cumulate crystals and residual liquid. Unlike radiogenic isotopes, stable isotopes are also fractionated by low temperature surface processes. Therefore, they offer a potentially important means by which recycled crustal material can be distinguished from intra-mantle fractionation processes. 

Friedman I, O Neil JR (1977) Compilation of stable isotope fractionation factors of geochemical interest. In Data Geochem, 6th ed Geol Surv Prof Pap 440KK Friedman I, Scholz TG (1974) Isotopic composition of atmospheric hydrogen (1967-1969). J Geophys Res 79 785-788... 

Horita J (1988) Hydrogen isotope analysis of natural waters using an H2-water equilibration method a special implication to brines. Chem Geol 72 89-94 Horita J (1989) Stable isotope fractionation factors of water in hydrated salt minerals. Earth Planet Sci Lett 95 173-179... 

The fractionation of stable isotopes between two substances A and B can be expressed by use of the isotope fractionation factor alpha (a),... 

Chacko, T., Cole, D.R., and Horita, J. (2001) Equilibrium oxygen, hydrogen and carbon isotope fractionation factors applicable to geologic systems. In Reviews in Mineralogy and Geochemistry Stable Isotope Geochemistry (Valley, J.W., and Cole, D.R., eds.), Vol. 43, pp. 1-81, Mineralogical Society of America, Chantilly, VA. 

The domain of the search for an improved separation process was defined by certain criteria (a) isotopic fractionation should be achieved by means of a two-phase, chemical exchange reaction which was amenable to countercurrent operation in a multistage contactor at ambient temperature and pressure (b) the single-stage isotopic fractionation factor for the reaction should be appreciably larger than that for the distillation of Me20 BF3 (c) the molecular species in each process stream should be thermally refluxable—i,e, convertible from one species to the other by the addition or removal of heat alone (d) process materials should be more stable with respect to irreversible decomposition than those used in the (CH3)20 process and (e) the chemical form of the product should permit a ready, quantitative conversion of the separated isotopes to the elemental state. 

Schematic diagram of the exchanges and stable carbon isotope ratios among the reservoirs of atmospheric CO2, ocean HCO3 and CO2, solid organic carbon (Cqm) and CaC03 and CH4. Numbers under the chemical symbols represent the isotopic ratio in %o. See Table 5.3 for an estimate of the fractionation factors.

Schematic diagram of the stable nitrogen isotope ratios of different nitrogen reservoirs in the sea. The general range of stable isotope ratios (with respect to the atmosphere) found in nature is given in the boxes and the difference fractionation factors e (in %o) accompany arrows between the boxes. Many of the values are approximations because of the wide variations of observations. See Table 5.3 for more details of some of the reactions and the text for explanation. Values are based on data presented by Altabet and Small (1990), Altabet and Francois (1994) and Sigman and Casciotti (2001).

The Rayleigh distillation equation was developed to mathematically describe this t5q>e of cumulative isotope effect. It relates the initial (Rq) and transient (RJ stable isotope ratios of a reservoir to the fraction (f) of the initial material that remains (often expressed at the concentration ratio, Q/Cq of the more abundant isotope) when product is removed with a constant fractionation factor, a, over a time, t... 

Friedman, I. O Neil, J.R. (1977) Compilation of Stable Isotopic Fractionation Factors of Geochemical Interest. US Geol. Surv. Prof. Pap., 440-KK, 12 pp. 

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