Hydrogen Isotope Fractionation Research Articles

Site specific isotope fractionation of hydrogen in the oxydation of ethanol into acetic acid. Application to vinegars

The origin of vinegars obtained by bacterial or chemical oxidation of ethanol resulting from the fermentation of various sugars is identified by a new method based on NMR determination of site specific deuterium/hydrogen ratio in acetic acid.

Carbon and hydrogen isotope fractionation resulting from anaerobic methane oxidation

Carbon and hydrogen isotope fractionation resulting from anaerobic methane oxidation

Isotopic exchange in mineral-fluid systems. II. Oxygen and hydrogen isotopic investigation of the experimental basalt-seawater system

Oxygen and hydrogen isotopic exchange reactions between basalt and seawater at T = 300° to 500°C were investigated, using oceanic tholeiitic basalt ( δ 18O = ∼5.7%.; δD = ∼−70%. ), natural seawater ( δ 18O = 1.2%.; δD = + 5%. ) and artificial seawater ( δ 18O = −5.3%. ) as starting materials. The starting basalts varied in the crystallinity (from holocrystalline to glass) but were ground to approximately the same grain size (−100 mesh). The water/rock mass ratios ranged from 1 to 3 and the duration of the experiments ranged from 167 to 576 days. In general, depletion of 18O and enrichment of D in basalts occur at all temperatures, with the magnitudes of change being greater as temperature, time and to a lesser degree, glass content increases. The trends in isotopic shifts are directly related to changes in the style and intensity of mineralogic alterations in the basalt ( e.g., smectite at 300°C, talc-actinoiite at 400°–500°C). The changes in the δ 18O values of basalts and seawater in the experimental systems were observed to follow closely with those expected from a first-order rate law. Rate constants for the oxygen isotopic exchange between rock and water range from 10 −9.5 to 10 −8.0 moles oxygen/m 2 of solid surface/sec for temperatures of 300° to 500°C. The activation energy for the isotopic exchange reaction was calculated to be 11.5 Kcal/ mol. An application of our experimental rate data to natural systems suggests that the oxygen isotope equilibrium between basalt and seawater in the mid-oceanic ridge may take place within approximately 1000 years at 350°C. Our experimental data also suggest the equilibrium oxygen isotopic fractionation factors between the altered basalt and seawater to be 3.5 ± 0.5%. at 300°C, 2.0 ± 0.4%. at 400°C and 0.5 ± 0.25%. at 500°C. The observed hydrogen isotopic fractionation factors between the altered basalts and seawater in our experimental systems were about −74%. at 300°C. about −62%. at 400°C and about −48%. at 500°C. These fractionation factors are probably attributable to the equilibrium fractionation between Fe-rich secondary phases and seawater.

Hydrogen and carbon isotope fractionation during experimental production of bacterial methane

This paper presents C and H isotope compositions of compounds involved in methane production by pure cultures of Methanobacterium formicicum. The C isotope compositions of the methane produced and of the residual CO 2 are compared to data observed in natural conditions in marine sediments. This comparison leads to further evidence that CO 2 reduction is an important mechanism for microbial generation of methane in deep marine sediments. The H isotope compositions show involvment of the water hydrogen into methane as well as hydrogen exchange between water and molecular hydrogen in the course of CO 2 reduction. A mechanism is proposed as a possible explanation for the data obtained involving conjugated reactions of CO 2-reduction and enzymatic reduction of water.

Hydrogen isotope study of the granitic rocks of the Ryoke belt, Central Japan

Among many Cretaceous granitic masses in the Ryoke belt of central Japan, two discordant plutons, Kisokoma and Shinshiro, and the largest batholith, Inagawa, were investigated for the D/H ratio in coexisting biotite and hornblende. The relationships between δD- and X Fe- [= Fe/(Fe + Mg)] values for coexisting biotite and hornblende in the three granitic masses are markedly different. In the Kisokoma pluton, tielines between coexisting biotite and hornblende on the δ D— X Fe diagram are distributed in a narrow area and slopes of the tielines are essentially parallel to that derived from T. Suzuoki and S. Epstein's experimental work. In the Shinshiro pluton the tielines are distributed in two areas though the slopes are also almost parallel to that of Suzuoki and Epstein. In the Inagawa batholith, most of the tielines are nearly vertical with highly scattered δ D-values. The X Fe-values of the minerals are ∼ 0.5 in the Kisokoma and Shinshiro plutons, and ∼ 0.7 in the Inagawa batholith. Such a difference in the δ D— X Fe relationship is explained by the different geological conditions of intrusion of the three granitic masses. Namely, the Kisokoma and Shinshiro plutons are discordant, and the erosion level of the former is shallow and that of the latter is deep. The Inagawa batholith intruded during the geologic movement and interacted with the country rocks. On the basis of Suzuoki and Epstein's experimental work, the δ D-value of the water in a single granitic magma can be estimated to be as low as −60 to −70‰ in the initial stage, and as high as ∼ −30‰ in the later stage, because of the early crystallization of biotite and hornblende, whose δ D-values are usually lower than the value of water in the magma. When the experimental results for hornblende by C.M. Graham et al. and those for biotite by Suzuoki and Epstein are combined, the temperature of the hydrogen exchange equilibration between biotite and magmatic water is calculated to be from 400° to 630°C for the Kisokoma pluton, and from 650° to 800°C for the Shinshiro pluton. It is impossible to estimate the equilibration temperature for the Inagawa batholith, because there are no experimental data on hydrogen isotope fractionation between hydrous silicates, such as biotite and hornblende, with higher X Fe-values than 0.7 and coexisting water.

Hydrogen isotope fractionation in the system H 2O-liquid NaAlSi 3O 8: new data and comments on D/H fractionation in hydrothermal experiments

Measurements in the system H2O-NaAlSi3O8 at P = 2 kbar and T = 870 and 1250°C indicate that the vapour is enriched in D relative to the silicate melt by 8 to 25‰. The large error margins of the data are due to the important changes in the isotopic compositions of the charges that are caused by the kinetic fractionations associated with hydrogen diffusion through platinum capsules in high-temperature, high- pressure experiments. A new interpretation of theseeffects is presented, and it is concluded that the equilibrium hydrogen fractionation should be at least 25‰ between 870 and 1250°C at 2-kbar pressure.

Biogenic methane formation in marine and freshwater environments: CO 2 reduction vs. acetate fermentation—Isotope evidence

Two primary methanogenic pathways can be distinguished using the carbon and hydrogen stable isotope composition of the methane as a function of the coexisting carbon dioxide and formation water precursors. Although both pathways may occur in both marine and freshwater sediments. CO 2 reduction is dominant in the sulphate-free zone of the former, while acetate fermentation is the major pathway in freshwater sediments. Methane in marine sediments can be defined isotopically by δ 13 C −110 to −600/%., and δD −250 to −1700‰. In contrast, methane from freshwater sediments ranges from δ 13C −65 to −500/%. and δD −400 to −2500/%.. Carbon isotope fractionations ( α c CO 2- CH 4) are generally between 1.05 and 1.09 for marine sediments, while lower in freshwater sediments (1.04 to 1.06). The relationship of the methane to the formation water indicates the source of the hydrogen for CO 2 reduction to be the water directly with an associated hydrogen fractionation of −180 ± 200/%.. The CH 4-H 2O hydrogen fractionation is larger for acetate fermentation due to the transfer of the methyl group during methanogenesis which is depleted in deuterium and accounts for 3 4 of the hydrogen in the methane. A model is presented showing that the fourth hydrogen via acetate fermentation may ultimately come from the formation water but is isotopically fractionated. Combination of the carbon and hydrogen isotope fractionations ( α C , α D ) from CH 4 with CO 2 and H 2O respectively, can clearly delineate the CO 2 reduction and acetate fermentation environments. Defining the character of the methanogenic types with carbon and hydrogen isotopes not only provides information about the environment of formation, it is also most useful in distinguishing biogenic from thermogenic methane gases.

Hydrogen isotope fractionation during the hydrolysis of starch and the fermentation of d-glucose to ethanol

Hydrogen isotope fractionation during the hydrolysis of starch and the fermentation of d-glucose to ethanol

Hydrogen Isotope Disproportionation and Fractionation Equilibria in the H2O--D2O Solvent System. IV. Fractionation of Deuterium between 3,3-Dimethyl-2-butanone and Water.

Hydrogen Isotope Disproportionation and Fractionation Equilibria in the H2O--D2O Solvent System. IV. Fractionation of Deuterium between 3,3-Dimethyl-2-butanone and Water.

Hydrogen Isotope Disproportionation and Fractionation Equilibria in H2O/D2O/Solvent System. V. Fractionation of Deuterium between Methyl Phenyl Ketone and Water.

Hydrogen Isotope Disproportionation and Fractionation Equilibria in H2O/D2O/Solvent System. V. Fractionation of Deuterium between Methyl Phenyl Ketone and Water.

An integrated chemical and stable‐isotope model of the origin of Midocean Ridge Hot Spring Systems

Chemical and isotopic changes accompanying seawater‐basalt interaction in axial midocean ridge hydrothermal systems are modeled with the aid of chemical equilibria and mass transfer computer programs, incorporating provision for addition and subtraction of a wide‐range of reactant and product minerals, as well as cation and oxygen and hydrogen isotopic exchange equilibria. The models involve stepwise introduction of fresh basalt into progressively modified seawater at discrete temperature intervals from 100° to 350°C, with an overall water‐rock ratio of about 0.5 being constrained by an assumed δ18OH2O at 350°C of +2.0 per mil (H. Craig, personal communication, 1984). This is a realistic model because: (1) the grade of hydrothermal metamorphism increases sharply downward in the oceanic crust; (2) the water‐rock ratio is high (>50) at low temperatures and low (<0.5) at high temperatures; and (3) it allows for back‐reaction of earlier‐formed minerals during the course of reaction progress. The results closely match the major‐element chemistry (Von Damm et al., 1985) and isotopic compositions (Craig et al., 1980) of the hydrothermal solutions presently emanating from vents at 21°N on the East Pacific Rise. The calculated solution chemistry, for example, correctly predicts complete loss of Mg and SO4 and substantial increases in Si and Fe; however, discrepancies exist in the predicted pH (5.5 versus 3.5 measured) and state of saturation of the solution with respect to greenschist‐facies minerals. The calculated δDH2O is +2.6 per mil, in excellent agreement with analytical determinations. The calculated chemical, mineralogic, and isotopic changes in the rocks are also in good accord with observations on altered basalts dredged from midocean ridges (Humphris and Thompson, 1978; Stakes and O'Neil, 1982), as well as with data from ophiolites (Gregory and Taylor, 1981). Predicted alteration products include anhydrite and clay minerals at low temperatures and a typical albite‐epidote‐chlorite‐tremolite (greenschist) assemblage at 350°C. The models demand that the major portion of the water‐rock interaction occur at temperatures of 300°–350°C. Interaction at temperatures below approximately 250°C results in negative δ18OH2O shifts, contrary to the observed positive δ18O values of the fluids exiting at midocean ridge vents. Hydrogen isotope fractionation curves by Suzuoki and Epstein (1976), Lambert and Epstein (1980), and Liu and Epstein (1984), among others, are compatible with the model, and require δDH2O to increase at all temperatures as a result of seawater‐basalt interaction.

A proposed neutron diffraction experiment to measure hydrogen isotope fractionation in solution

A novel method for investigating solute–solvent H/D exchange equilibria in aqueous solution is described. The ‘‘first-order difference’’ neutron diffraction method of Enderby and co-workers is combined with a variation of the isotopic composition of the solvent, ideally from pure D2O to that D2O–H2O mixture in which the average neutron scattering length of the H and D species vanishes. The new technique can give the location of the exchange site with respect to a particular atom as well as the H/D exchange constant for the site with reference to the bulk solvent. The relevant solution thermodynamic data are reviewed to identify systems for which the proposed neutron diffraction experiment is feasible. The literature data are complemented by new calculations of the effect of an ion on the O–H stretch vibration and the libration of the neighboring water. For +3 ions the dominant isotope effect is associated with the O–H stretch of the water; the shift to lower frequencies is proportional to the square of the ionic charge z in the sequence Na+, Mg2+, Al3+, while the libration frequency increases linearly with z in the same series. The reported free energy data for H2O to D2O transfers of various Mz+ ions can be understood on the basis of these observations. Finally, while the question of feasibility of the new technique invites examination of the details of ionic hydration, the main point is that such details could be elucidated by the proposed diffraction technique.

Fractionation of hydrogen and oxygen isotopes between hydrated and free water molecules in aqueous urea solution

Ratios of D/H and /sup 18/O//sup 16/O in the vapor phase in equilibrium with aqueous urea solution with different urea molalities were measured at 15 and 25/sup 0/C. Under the assumption that urea solutions consist of two species, i.e., the urea-water cluster and free water, the results are interpreted to give the average hydration number, i.e., the number of water molecules per urea molecule in the urea-water cluster. Good agreement was obtained for the hydration number estimated independently from hydrogen and oxygen isotopic fractions. On the basis of hydrogen isotopic data at 25/sup 0/C, the average hydration number of urea in the cluster is 6.3 +/- 0.8 at 2.1 m and 2.75 +/- 0.08 at saturation (20.15 m). The corresponding average hydration numbers based on oxygen isotopic data were calculated to be 6.7 +/- 2.4 at 2.1 m and 2.75 +/- 0.25 at urea saturation. HD/sup 16/O is enriched in the urea-water cluster and H/sub 2//sup 18/O is enriched in free water. Isotopic partitioning between the cluster and free water is markedly different from those between hydration spheres and free water in aqueous electrolyte solutions. 29 references, 6 figures, 5 tables.

Genesis and evolution of water in a two-mica pluton: A hydrogen isotope study

Measurements were made of the hydrogen isotope composition of 74 samples of muscovite, biotite, vein quartz and whole rocks from the Papoose Flat pluton, eastern California, U.S.A., and adjacent metamorphic and sedimentary rocks in order to elucidate the genesis and evolution of water and hydrous minerals in a two-mica granodiorite. Electron microprobe analyses were made of all micas so that the Suzuoki-Epstein equation could be used in evaluating the data. Based on experimental, theoretical and textural evidence of mica paragenesis, a model of hydrogen isotope fractionation between an aqueous vapor and a magma during crystallization has been constructed. This model accounts for the observed hydrogen isotope relations and implies that primary hydrogen isotope compositions have been preserved in a large portion of the pluton. The δ D-values of biotites vary widely over the range −103 to −66% with most values lying between −90 and −70‰ Muscovites, on the other hand, are isotopically more uniform and have δ D-values of −61 to −41‰ with most values lying between −50 and −46‰ These data are consistent with the interpretation that biotite formed over a long period of crystallization whereas muscovite formed in a narrow interval, presumably during the final stages of crystallization when alumina and water contents were at their highest. Only 8 of the 21 muscovite-biotite pairs analyzed are in hydrogen isotope equilibrium as calculated from the Suzuoki-Epstein equation. Biotites in the western half of the pluton have relatively low δ D-values of around −85‰, whereas those in the eastern half have higher values of up to −66‰ This pattern is a consequence of a loss of permeability associated with the syn-intrusive deformation of the western margin of the pluton. This loss of permeability enhanced the preservation of primary hydrogen isotope relations there by diverting water evolved from the magma out through the eastern half of the pluton where some deuteric exchange is documented. A much larger metamorphic aureole with extensive retrograde textures around the eastern end of the pluton attests to the passage of this water.

The hydrogen isotope fractionation between kaolinite and water

Hydrogen isotope fractionation factors between kaolinite and water were determined at temperatures between 200° and 352°C. Five-gram samples of kaolinite were heated in contact with 8-mg samples of water in sealed glass reaction tubes. Under these conditions the approach to equilibrium with time will be reflected primarily in the change of the δ D in the water. Also the δ D of the hydrogen in the kaolinite will be relatively constant, subject to minor corrections. About seventy sealed vessels were heated for various times at various temperatures. During four months of heating, ∼ 25% of kaolinite hydrogen exchanged with the water at 200°C, whereas 100% exchanged at 352°C. The α-values were estimated assuming equilibrium between exchanged kaolinite and water. The 10 3lnα-values are estimated to be −20, −15, −6 and +7 for 352°, 300°, 250° and 200°C, respectively, which are in approximate agreement with reported values previously determined at 400°C using conventional methods as well as those estimated from kaolinite in hydrothermally active systems. The curve representing the relationship between the hydrogen isotope fractionation factor for the kaolinite-water system and temperatures between 400° and 25°C is not monotonic but rather has a maximum at 200°C.

Carbon and hydrogen isotopic compositions of algae and bacteria from hydrothermal environments, Yellowstone National Park

Stromatolites forming today on a small scale in hydrothermal environments are chemical and biological analogues of much larger Precambrian formations. Carbon isotopic composition varied as a function of CO2 concentration, pH, and species composition. Stratiform, layered stromatolites grew in silica-depositing springs at 55° to 70°C; they consisted mainly of a unicellular alga, Synechococcus, and a filamentous, photosynthetic bacterium, Chloroflexus. These thermophiles become enriched in 12C as the concentration of carbon dioxide in the effluent waters increases. At a concentration of 40 ppm total inorganic C, and δ13C of organic carbon was ∼ −12%., whereas at 900 ppm total inorganic C, the δ13C of similar species was ∼ −25%.. Conical stromatolites or conophytons (principally a filamentous, blue-green alga Phormidium and Chloroflexus) grew at 40°-55°C. In older, broader conophytons, Chloroflexus was the dominant organism. Their δ13C values were ∼ −18%. in a variety of hot springs. In carbonate-depositing springs, i.e., carbon dioxide saturated, conophytons and stromatolites consisting of a variety of blue-green algae and photosynthetic bacteria had the most negative δ13C values (to −30%.). These carbon isotope ratios are directly comparable to carbon isotope ratios of kerogen from Precambrian stromatolites. The presence and activity of methanogenic bacteria or heterotrophic, aerobic and anaerobic bacteria did not alter significantly the δ13C of the original organic matter.The hydrogen isotopic fractionation between thermophilic organisms and water is 0 to −74 for temperatures of 85° to 46°C, respectively. Acidophilic algae fractionated hydrogen isotopes to a lesser extent than did the photosynthetic organisms inhabiting neutral pH springs. Because organic matter retains some of its original isotopic signature, relationships of CO2 levels, pH, temperature, and species composition between modern stromatolites and their environment and those of the Precambrian can be inferred.

Hydrogen Isotope Disproportionation and Fractionation Equilibria in H2O--D2O Solvent System. III. Fractionation of Deuterium between Methoxymethyl Phenyl Ketone and Water.

Hydrogen Isotope Disproportionation and Fractionation Equilibria in H2O--D2O Solvent System. III. Fractionation of Deuterium between Methoxymethyl Phenyl Ketone and Water.

Hydrogen isotopic fractionation factor between brucite and water in the temperature range from 100� to 510� C

The hydrogen isotopic fractionation factor between brucite and water has been determined in the temperature range of 100°–510° C. Brucite is always depleted in deuterium relative to the coexisting water, and the degree of depletion becomes larger with decreasing temperature. The fractionation factor changes smoothly in the temperature range of 144°–510° C and its temperature dependence was obtained by the method of least square fit in the following form: 103Inα=8.72×106T−2−3.86×104T−1+14.5

Stable hydrogen isotopes in iron oxides—isotope effects associated with the dehydration of a natural goethite

The dehydration of a natural goethite to hematite is accompanied by a systematic hydrogen isotope fractionation. Closed system dehydration at, and below, 250°C results in a significantly greater degree of isotopic fractionation than does open system dehydration. This relationship is apparently reversed at 300°C. Both processes produce a progressive decrease in the D H ratio of the mineral hydrogen with increasing degree of dehydration. At temperatures of 160°C to 250°C the closed system mineralvapor fractionation factor is independent of temperature, while above 250°C, it varies strongly with temperature. The mineral-vapor fractionation factor associated with open system dehydration appears to be independent of temperature over the interval 160°C to 300°C. The closed system D H fractionation suggests that natural goethite undergoing dehydration in the presence of water can isotopically exchange with that water. CO 2 loss from goethite during dehydration is correlated with the loss of H 2O. The CO 3 is thought to be present in carbonates which exist as impurities in the goethite. Loss of both H 2O and CO 2 appears to be diffusion-controlled.

D/H ratios of coals and the palaeolatitude of their deposition

Various interpretations of D/H ratios in coals have been suggested1–4. The factors most likely to influence these ratios seem to be: (1) prevailing climatic conditions and the related deuterium contents of available fresh water (precipitation) during plant growth; and (2) the fractionation of stable hydrogen isotopes during both plant growth and subsequent sediment maturation. On theoretical grounds, the global distribution of the hydrogen isotopes in precipitation is expected to favour an increased deuterium concentration at the Equator relative to the poles. Published measurements of the D/H ratio in present day precipitation at different latitudes, as shown in Fig. 15, follow this trend. Clearly the well-established global variation in the isotopic composition of precipitation with regard to both climate and latitude provides a reasonable explanation for the differences observed in D/H ratios for coal from different continents as has been proposed for coals from Germany and South Africa1, and for isotopic variations seen in peat2. The D/H ratios for Australian coals reported here are consistent with their respective latitudes of deposition predicted from continental drift and hence the implied dependence on palaeoclimate.