Fractionation, isotopic

Isotope effects, as they can be observed in phase transition or dissociation reactions, are usually the result of incomplete processes in diffusive or equilibrium 

The velocity ratio of both CO2 species explains that the average velocity of C02 is 1.13% higher than that of the heavier molecule. 

Boiling water will lose primarily the light molecules as can be seen in 

Equilibrium isotope effects usually are associated with phase transition processes such as evaporation, diffusion or dissociation reactions. When incomplete phase transition processes occur during sample preparation, they lead to severe alteration of the initial isotope ratio. In fact, and that is of highest importance for all sample preparation steps in IRMS, only complete conversion reactions are acceptable to maintain the integrity of the original isotope ratio of the sample. 

The natural variations in isotopic abundances can be large, depending on the relative elemental mass differences hydrogen (100%) oxygen (12.5%) carbon (8.3%) nitrogen (7.1%), see also Table 2.48 (Rossmann, 2001 Rosman and Taylor, 

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Examination of possible systems for boron isotope separation resulted in the selection of the multistage exchange-distillation of boron trifluoride—dimethyl ether complex, BF3 -0(CH3 )2, as a method for B production (21,22). Isotope fractionation in this process is achieved by the distillation of the complex at reduced pressure, ie, 20 kPa (150 torr), in a tapered cascade of multiplate columns. Although the process involves reflux by evaporation and condensation, the isotope separation is a result of exchange between the Hquid and gaseous phases. 

Kinetic isotope effects are an important factor in the biology of deuterium. Isotopic fractionation of hydrogen and deuterium in plants occurs in photosynthesis. The lighter isotope is preferentially incorporated from water into carbohydrates and tipids formed by photosynthesis. Hydrogen isotopic fractionation has thus become a valuable tool in the elucidation of plant biosynthetic pathways (42,43). 

R. W. FairbriiXjE, Encyclopedia of Geochemistry and Environmental Sciences, Van Nostrand, New York, 1972.. See sections on Geochemical Classification of the Elements Sulfates Sulfate Reduction-Microbial Sulfides Sulfosalts Sulfur Sulfur Cycle Sulfur Isotope Fractionation in Biological Processes, etc., pp. 1123 - 58. 

Equilibrium isotopic fractionations explain the gross behavior of and i5D in precipitation of mid to high latitudes. 

Krueger, H.W. and Sullivan, C.H. 1984 Models for carbon isotope fractionation between diet and bone. In Tumland, J.R. and Johnson, P.E., eds.. Stable Isotopes in Nutrition. Washington D.C, American Chemical Society Symposium Series, No. 258 205-220. 

Delwiche, C.C. and Steyn, P.L. 1970 Nitrogen isotope fractionation in soils and microbial reactions. Environmental Science and Technology 4 929-935. 

Mariotti, A., Germon, J.C., Hubert, P., Kaiser, R, Letolle, R., Tardieux, A. and Tardieux, P. 1981 Experimental determination of nitrogen kinetic isotope fractionation some principles illustration for the denitrification and nitrification processes. Plant and Soil 62 413-430. 

Mariotti, A., Mariotti, F., Champigny, M.L., Amarger, N. and Moyse, A. 1982 Nitrogen isotope fractionation associated with nitrate reductase activity and uptake of NO3by pearl millet. Plant Physiology 69 880-884. 

O Leary, M.H. 1981 Carbon isotope fractionation in plants. Phytochemistry 20 553-567. 

Shearer, G., Duffy, J., Kohl, D.H. and Commoner, B. 1974 A steady-state model of isotopic fractionation accompanying nitrogen transformations in soil. Soil Science Society of America... 

Farquhar, G.D., Ball, M.C., von Laemmer, S. and Roksandic, Z. 1982 Effect of salinity and humidity on 5 C values of halophytes. Evidence for diffusional isotope fractionation determined by the ratio of intercellular atmospheric COj under different environmental conditions. 

Emrich, K., Emhalt, D.H. and Vogel, J.C. 1970 Carbon isotope fractionation during the precipitation of calcium carbonate. Earth and Planetary Science Letters 8 363-371. 

The second analytical method uses a combustion system (O Neil et al. 1994) in place of reaction with BrF,. This method was used for the crocodiles because they were represented by very thin caps of enamel. The enamel was powdered and sieved (20 mg), pretreated in NaOCl to oxidize organic material and then precipitated as silver phosphate. Approximately 10-20 mg of silver phosphate were mixed with powdered graphite in quartz tubes, evacuated and sealed. Combustion at 1,200°C was followed by rapid cooling in water which prevents isotopic fractionation between the CO2 produced and the residual solid in the tube. Analyses of separate aliquots from the same sample typically showed precisions of 0.1%o to 0.4%o with 2 to 4 repetitive analyses even though yields are on the order of 25%. 

Bryant, J.D. and Froelich, P.N. 1995 A model of oxygen isotope fractionation in body water of large mammals. Geochimica et CosmochimicaActa 59 4523-4537. 

Wong, W.W., Cochran, W.J., Klish, W.J., Smith, E.O.B., Lee, L.S. and Klein, P.D. 1988 In vivo isotope-fractionation factors and the measurement of deuterium- and oxygen-18-dilution spaces from plasma, urine, saliva, respiratory water vapor, and carbon dioxide. American Journal of Clinical Nutrition 47 1-6. 

Bada, XL., Schoeninger, M.J. and Schimmelmann, M. 1989 Isotopic fractionation during peptide bond hydrolysis. Geochimica et CosmochimicaActa 53 3337-3341. 

Figure 10.4. Effect on apatite-collagen isotopic fractionation due to inhibition of amino acid production and preferred use of exogenous amino acids. Carnivore and herbivore, both based on C3 plants, have similar bulk isotopic composition of total edible tissues (T), leading to similar 5 C for apatite carbonate (AP). Collagen (CO) of carnivore is more enriched in Cthan that of herbivore, because of preferential utilization of amino acids derived from protein (P) of herbivore flesh in construction of carnivore s proteins. C ss = assimilated carbon.

The applicability of the linear-mixing model is seen most prominently in the interpretation of the 5 C of bone apatite which has been shown to represent the total diet, rather than being derived from energy foods , as was previously proposed by some authors. Although 5 C,p should represent total diet, the isotopic fractionation between this component and total diet appears to be somewhat variable, suggesting that more definite knowledge about this fractionation is needed if we are to use 5 C,p as an index of total dietaiy 5 C values. 

The author has benefited greatly from discussions with Professors Karl Freeman, Evert Nieboer and Stephanie Atkinson on biochemistry and nntri-tion. Boaz Luz clarified my ideas about carbon isotope fractionation in blood. Research was supported by a grant from the Social Sciences and Humanities Research Council. The author thanks Shannon Coyston, Lori Wright, Chris White and Stanley Ambrose for useful comments and discussions. 

Grossman, E. and Ku, T.-L. 1986 Oxygen and carbon isotope fractionation in biogenic aragonite temperature effects. Chemical Geology (Isotope Geoscience Section) 59 59-74. 

Mook, W.G., Bommerson, J.C. and Staverman, W.H. 1974 Carbon isotope fractionation between dissolved bicarbonate, and gaseous carbon dioxide. Earth and Planetary Science Letters 22 169-176. 

THE REPRESENTATION OF ISOTOPIC FRACTIONATION BETWEEN DIET AND BODY COMPONENT... 

Any body tissue in direct equilibrium with the major excretum should reflect the isotopic composition of the diet as a whole. This seems to be the case for bioapatite carbonate, which is thought to be in equilibrium with plasma bicarbonate, which itself is in equilibrium with respired CO2. In fact the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data sets (among others) show clearly that the bioapatite carbonate differs from total diet (or respired CO ) by an amount approximating to the equilibrium isotopic fractionation in the system (Mook 1989) ... 

Figure 11.1. A flow-model scheme for treating the protein routing question. Labels refer to flow rates of carbon. The total carbon flux, into and out of the body, is 1, divided into F (for protein) and 1 - F for the remainder. The significant relevant internal fluxes are between the amino acid pool (coupled to the body protein pool), and the energy metabolism pool . The extent to which protein routing is observable in the body protein composition depends on the value ofX (See Fig. 11.2). Numbers in refer to suggested isotopic fractionations associated with a metabolic path, which are consistent with the data of the Ambrose and Norr (1993) and Tieszen and Fagre (1993) data set (see Section 4.1).

If all the relevant fluxes are in steady state, we can write equations for each flux and solve for the system as a whole, thereby relating the composition of the collagen to the composition of the diet, to F and to X. Assume, as a first approach, no isotopic fractionation takes place within the organism. We find ... 

A simplest possible flow-model (Fig. 11.1) has been formulated to account for collagen and for bioapatite carbonate measurements, under conditions where the protein content in the diet is changing. Its predictions , in terms of the Dietary Isotope Fractionation Function (DIFF), have been made explicit. 

We would argue that it is the task of those aiming to reconstruct ancient diet as well as those aiming to imderstand how isotopic fractionation signatures are produced, to devise experiments and analyze the results in order to... 

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