Studies isotopic

With arcs, intense bombardment by ions and electrons and the heat produced at the electrodes cause sample molecules to be vaporized and broken down into their constituent elements. These sources are used particularly for analysis or isotope studies when the samples involved are inorganic, nonvolatile, and thermally very stable. 

The subject of natural benzaldehyde came to the forefront in 1984 when it was found that a natural benzaldehyde product, labeled "oil of benzaldehyde," was actually made synthetically by the air oxidation of toluene followed by careful fractionation to remove trace impurities. This finding was accomphshed by the Center for AppHed Isotopic Studies, University of Georgia, and involved measuring the amounts of and in that material. 

The designation Ac signifies acyl-oxygen fission, whereas A1 is alkyl-oxygen fission. When n-amyl alcohol was hydrolyzed in 0-enriched water, the 0 appeared in the product acid rather than the alcohol, showing that alkyl-oxygen fission could not have occurred. Carpenter gives many examples of isotopic studies. 

Hydrogen as it occurs in nature is predominantly composed of atoms in which the nucleus is a single proton. In addition, terrestrial hydrogen contains about 0.0156% of deuterium atoms in which the nucleus also contains a neutron, and this is the reason for its variable atomic weight (p. 17). Addition of a second neutron induces instability and tritium is radioactive, emitting low-energy particles with a half-life of 12.33 y. Some characteristic properties of these 3 atoms are given in Table 3.1, and their implications for stable isotope studies, radioactive tracer studies, and nmr spectroscopy are obvious. 

Concerns over atmospheric methane as a greenhouse gas and the large contribution of biomethanogenesis as a source of this gas make it important to determine the relative significance of various components of this activity. A recent paper (8) summarized estimates (28-30) of source fluxes of atmospheric methane based on several carbon isotopic studies and presented new data on natural sources and biomass burning. These data (Table III) show that of a total flux of 594 million tons (Tg) per year, 83% is produced via biomethanogenesis from a combination of natural (42%) and anthropogenic (41%) sources. 

The prevalence of sulfur s second most abundant isotope, S, along with the fractionation known to occur in many biogeochemical processes, make isotopic studies of sulfur a potentially fruitful method of unraveling its sources and sinks within a given reservoir. 

Reid DJ, Quinn GP, Lake PS et al (2008) Terrestrial detritus supports the food webs in lowland intermittent streams of south-eastern Australia a stable isotope study. Freshw Biol 53 2036-2050... 

Schoeninger, M.J. and Moore, K. 1992 Bone stable isotope studies in archaeology. Jowrtta/ of World Prehistory 6 247-296. 

Five other isotope studies of Maya skeletal populations in Belize are available for comparison with Cuello (Table 2.4 Fig. 2.3). These include a time series from Preclassic to Historic at Lamanai (White and Schwarcz 1989), an Early through Terminal Classic sequence at Pacbitun (White et al. 1993),... 

Stable carbon isotope studies of Swartkrans fossils. In C.K. Brian, ed., Swartkrans, A... 

Nadelhoffer, K.J. and Fry, B. 1994 Nitrogen isotope studies in forest ecosystems. In Lajtha, K. and Michener, R.H., eds.. Stable Isotopes in Ecology and Environmental Science. Blackwell Scientific Publications 22 4. 

In parallel developments, oxygen isotope studies based on the stable phosphate ion in calcified tissues have been found to be more successful using enamel than bone as sample material (Ayliffe et al. 1994 Bryant et al 1994), and similarly oxygen isotopes from the less stable C—0 bond in enamel carbonate seems to be more predictable (Bocherens et al. 1996). Researchers exploring the relationship between Electron Spin Resonance (ESR) and carbonate content in enamel have found that dates are mostly consistent when carbonate levels did not deviate much from biogenic levels (Grun et al. 1990 Rink and Schwarcz 1995). 

Cerling, T.E., Bowman, J.R. and O Neil, J.R 1988 An isotopic study of a fluvial-lacustrine... 

Pearson, FJ. and Coplen, T.B. 1978 Stable isotope studies of lakes. In Lerman, A., ed., Lakes-Chemistry, Geology, Physics. New York, Springer-Verlag 325-339. 

Stable isotope studies in human evolution. Evolutionary Anthropology 4 83—98. 

In the following description and discussion of our results, various criteria derived from the literature are used to determine whether or not each sample is of adequate preservation to allow it to be confidently included in a stable isotope study. The values applied in the various criteria have been found to be associated with archaeological bone collagen that retained an isotopic composition that was reflective of its diet, while the majority of samples that had values outside of the criteria did not retain an isotopic composition that reflected diet. The values for these criteria may vary slightly depending upon the collagen extraction methodology used, and such criteria are not exact. In this study samples that fall within the criteria values are deemed acceptable, and those that do not are deemed unacceptable. ... 

Kreitler, C.W. 1975 Determining the Source of Nitrate in Ground Water by Nitrogen Isotope Studies. 

Heaton, T.H.E. (1987). Isotopic studies of nitrogen in the hydrosphere and atmosphere a review. Chemical Geology 0sotope Geoscience), Vol. 59, pp. 87-102. 

A number of hydrocarbon radicals having multiple bonds at the radical centre have also been trapped in inert matrices and studied by IR spectroscopy. Thus, ethynyl radical was obtained by vacuum UV photolysis (9) of matrix-isolated acetylene (Shepherd and Graham, 1987) as well as when acetylene and argon atoms excited in a microwave discharge were codeposited at 12 K (Jacox and Olson, 1987). An appearance of diacetylene bands was observed when the matrices were warmed up, while the absorptions of the radical C2H disappeared. Detailed isotopic studies of D-and C-labelled ethynyl radicals showed a surprisingly low frequency of the C=C bond stretching vibration at 1846 cm instead of c.2100cm for a true C=C triple bond (the band at 2104 cm was attributed to the... 

Tewes et al., using both precipitation and extraction separation techniques, observed essentially complete exchange within the separation time (1 min) during an isotopic study ( V) of this exchange. The media ranged from 0.3 M perchloric acid to 7 M hydrochloric acid reactant concentrations were 10 M. 

Silverman and Dodson made the first detailed isotopic study of this exchange system using the separation afforded by the addition of 2,2 -dipyridyl at pH 5, followed by the precipitation of the ferric iron with either ammonia or 8-hydro-xyquinoline. Dodson , using this separation method, had previously obtained an overall rate coefficient of 16 l.mole" sec at 23 °C for 0.4 M perchloric acid media. The exchange in perchlorate and perchlorate-chloride media was found to conform to a rate law, first order with respect to both total ferrous and ferric ion concentrations, with an observed rate constant (k bs) dependent on the hydrogen-ion concentration, viz. 

Wahl et al. have completed the first detailed isotopic study of this exchange reaction and have shown paths catalysed by cations ( , K", Ca, Ba, Ph4As and various tetraalkylammonium ions ) occur. The first order with respect to both Fe(CN)6 and Fe(CN) was confirmed, viz. 

Eichler and Wahl have attempted an isotopic study ( Os and Os) of the exchange reaction between Os(dipy)3 and Os(dipy)3 using a direct injection technique so that reaction times 7 x 10 sec were possible. With total osmium 10" M in aqueous sulphate media at 0 °C complete exchange was observed. The separation methods used were, (a) perchlorate precipitation (in presence of iron(II) carrier) and (6) extraction with p-toluenesulphonic acid in nitromethane, of the osmium(II) complex. A lower limit of 1 x 10 l.mole. sec was placed on the rate coefficient (0 °C, 3.0 M H2SO4). Dietrich and Wahl using the line broadening effect produced by Os(dipy)3 on the nmr spectrum of Os(dipy)3 have been able to propose a value of > 5x 10" l.mole . sec at 6 °C in D2O (0.14 M [Cr] and 5x10 M [D- ]). 

Ozaki, A. "Isotopic Studies of Heterogeneous Catalysis" Kodansha Ltd./Academic Press 1977. 

Davidova lA, LM Gieg, M Nanny, KG Kropp, JM Suflita (2005) Stable isotopic studies on -alkane metabolism by a sulfate-reducing bacterial enrichment culture. Appl Environ Microbiol. 71 8174-8182. 

Photochemical irradiation of dimethyl and diethyl sulphoxides yields the corresponding sulphone in the presence of air and a photosensitizer such as methylene blue in yields up to 99% . Sulphoxides are also oxidized when they act as traps for persulphoxides, the intermediate formed on reaction of a sulphide with photochemically generated singlet oxygen - , equation (9). Isotope studies have shown that such reactions proceed through a linear sulphurane intermediate . Persulphones also react with sulphoxides in a similar manner , equation (10). 

This estimate can be evaluated based on the strontium and sulfur isotopic studies... 

The most important conclusion derived from the isotopic studies mentioned above is that isotopic characteristics of Kuroko ore fluids were caused dominantly by seawater-volcanic rock interaction at elevated temperature and by the mixing of seawater with small portions of igneous water or the hydrothermal solution whose chemical and isotopic compositions are controlled by water-rock interaction under the rock-dominated condition and also small proportion of mixing of meteoric water. 

However, it cannot be decided at present which processes (degree of seawater-rock interaction or mixing ratio of seawater, igneous water and meteoric water) are important for the generation of Kuroko ore fluids solely from the isotopic studies. But experimental and theoretical considerations on seawater-volcanic rocks interaction and origin of hydrothermal solution at midoceanic ridges suggest that Kuroko ore fluids can be produced dominantly by seawater-volcanic rock interaction. 

Figure 1.178 represents a comparison between the stannite-sphalerite temperatures and homogenization temperatures of fluid inclusions or sulfur isotope temperatures. It can be seen in Fig. 1.178 that Nakamura and Shima s geothermometer would be rather consistent with the temperature estimated based on the fluid inclusions or sulfur isotope studies. It is notable that almost all stannite-sphalerite temperatures are within 30°C of average homogenization temperatures and sulfur isotope temperatures. 

Graham, C.M., Sheppard, S.M.F. and Healton, T.H.E. (1980) Experimental hydrogen isotope studies, I. Systematics of hydrogen isotope fractionation in the system epidote-H20, zoisite-H20 and AIO(OH)-H2O. Geochim. Cosmochim. Acta, 44, 353-364. 

Hamada, M. and Imai, A. (2000) Sulfur isotopic study of the Toyoha deposit, Hokkaido, Japan — Comparison between the earlier-stage and the later-stage veins. Resource Geology, 50, 113-122. 

Imai, A., Shimazaki, H. and Nishizawa, T. (1998) Hydrogen isotope study of fluid inclusions in vein quartz of the Hishikari gold deposits, Japan. Resource Geology, 48, 159-170. 

Kajiwara, Y. (1971) Sulfur isotope study of the Kuroko-ores of the Shakanai No. 1 deposit, Akita Prefecture, Japan. Geochem. 7.,4, 157-181. 

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