Natural abundance stable carbon isotopes

Jim, S., Ambrose, S. H. and Evershed, R. P. (2003b) Natural abundance stable carbon isotope evidence for the routing and de novo synthesis of bone FA and cholesterol. Lipids 38, 179 186. 

Natural Abundance Stable Carbon Isotopes (I3C). There are trends in 13C of plant, litter, and organic constituents in soil that can be used to investigate carbon cycling, but to date the trends have proven too subtle, the variation too high, or the mechanisms too poorly understood to exploit these patterns definitively. The 813C of plant litter and particulate SOM is typically close to that of the plant source,... 

Stable carbon isotopes (see Chap. 1) provide a promising new method of validating intrinsic bioremediation. Carbon has two stable isotopes, with 12C comprising 98.89% and 13C comprising 1.11% of the total natural abundance [476]. Because of the magnitude of this abundance gap, the ratios of 13C to 12C in carbon-bearing compounds are expressed as per mil (%o) differences relative to a standard (i.e., <513C vs PDB,see Chap. 1). 

Stable carbon isotope methods exploit natural variations in the relative abundances of the isotopes and and are valuable archaeological tools for the study of paleonutrition ... 

The use of the stable isotope as a tracer in biological research has become increasingly common as evidenced by recent bibliographies (1,2), The effective use of this isotope has been established in the field of nutrition, where it has been applied in human clinical studies (3,4), in food science research and in ecological studies of animal food habits (6,7) Many nutrition studies are carried out at natural abundance levels of C Because these levels are low and because differences in the content of natural materials are small, stable carbon isotope ratios (13q/1 ) expressed in relative terms as 6 values A value represents the per mil (parts per thousand) deviation of the content of the sample from the international PDB limestone standard, the value of which has been set arbitrarily to 0 /oo Thus, a value of -27 0 %o would mean that the sample contained 27 parts per thousand less than the PDB standard Although the PDB standard no... 

B.W. Bromley, G.D. Hegeman, W. Meinschein (1982) A method for measuring natural abundance intramolecular stable carbon isotopic distributions in malic acid. Anal. Biochem. 126. 436-446... 

This study described the application of a common analytical procedure adapted for compound-specific stable carbon isotope analyses of riverine contaminants. To evaluate the sensitivity of the analytical method and the precision of the isotopic data obtained a set of numerous substances at different concentration levels were measured. For most of the anthropogenic contaminants investigated (including chlorinated aliphatics and aromatics, musk fragrances, phthalate based plasticizers and tetrabutyl tin) acceptable carbon isotope analyses could be obtained down to amounts of approx. 5 ng. These amounts correspond to concentrations in water samples at a natural abundance level of low to medium contaminated river systems. However, it has to be considered that the accuracy as well as the sensitivity of the analytical method depend partially on the chemical properties of the substances measured. 

U.9 Phospholipid biosynthesis (general).- A few only of the very many papers published in this area that appear to have particular mechanistic importance can be described here. Stable carbon isotope ratios ( C/ C) at natural abundance levels were determined for each of the major fatty acid components of the phospholipids of E. coli. The results were consistent with a model of lipid metabolism in which fatty acids were released from the fatty acid synthase in free form, and required re-activation to the acyl-acyl carrier protein prior to esterification. A close coupling of fatty acid and phospholipid synthesis was implied. The characteristics of fatty acid transfer from acyl-acyl carrier protein to sn-glyoerol- -phosphate in E. coli have been inves-... 

Boron [7440-42-8] B, is unique in that it is the only nonmetal in Group 13 (IIIA) of the Periodic Table. Boron, at wt 10.81, at no. 5, has more similarity to carbon and siUcon than to the other elements in Group 13. There are two stable boron isotopes, B and B, which are naturally present at 19.10—20.31% and 79.69—80.90%, respectively. The range of the isotopic abundancies reflects a variabiUty in naturally occurring deposits such as high B ore from Turkey and low °B ore from California. Other boron isotopes, B, B, and B, have half-Hves of less than a second. The B isotope has a very high cross-section for absorption of thermal neutrons, 3.835 x 10 (3835 bams). This neutron absorption produces alpha particles. 

The elements whose isotopes are routinely measured with gas inlet mass spectrometers are carbon (12C and 13C, but not 14C), oxygen (160, 170, l80), hydrogen ( H, 2H, but not 3H), nitrogen (14N and 1SN) and sulphur (32S, 33S, 34). Stable isotopes of H, C, N, O, and S occur naturally throughout atmosphere, hydrosphere, lithosphere, and biosphere. They are atoms of the same elements with a different mass. Each element has a dominant light isotope with the nominal atomic weight (I2C, 160,14N, 32S, and H) and one or two heavy isotopes (l3C, nO, 180, 15N, 33S, 34S, and, 2H) with a natural abundance of a few percent or less Table 1). 

ISOTOPES There are 15 isotopes of carbon, two of which are stable. Stable carbon-12 makes up 98.89% of the elemenfs natural abundance in the Earth s crust, and carbon-13 makes up just 1.11% of carbon s abundance in the Earth s crust. All the other isotopes of carbon are radioactive with half-lives varying from 30 nanoseconds (C-21) to 5,730 years (C-14). 

This example illustrates how m/e values of ions that differ only in isotopic composition can be used to determine elemental compositions. The important isotopes for this purpose in addition to those of chlorine are the stable isotopes of natural abundance, 13C (1.1%), 15N (0.37%), 170 (0.04%), lsO (0.20%). As a further example, suppose that we have isolated a hydrocarbon and have determined from its mass spectrum that M + = 86 mass units. In the absence of any combination reactions there will be an (M + 1)+ ion corresponding to the same molecular ion but with one 13C in place of 12C. The intensity ratio (M + 1 )+/M+ will depend on the number of carbon atoms present, because the more carbons there are the greater the probability will be that one of them is 13C. The greater the probability, the larger the (M + 1 )+/M+ ratio. For n carbons, we expect... 

Smith, B.N., 1972. Natural abundance of the stable isotopes of carbon in biological systems. Bioscience, 22 226—231. 

Stable isotope (see Box 1.1) abundances cannot at present be determined with sufficient accuracy to be of use in studies of their natural variations. Mass spectrometers can, however, measure the relative abundances of some isotopes very accurately, resulting in stable isotope ratio measurements, for example oxygen —180/160, carbon — 13C12C and sulphur—3%/32S. Stable isotope ratios are reported in delta notation (8) as parts per thousand (%o per mil) relative to an international standard, i.e. ... 

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