Isotopes for carbon

The next higher mass peak, M+l, provides information on elemental composition. Table 22-1 lists the natural abundance of several isotopes. For carbon, 98.93% of atoms are, 2C and 1.07% are l3C. Nearly all hydrogen is H, with 0.012% 2H. Applying the factors in Table 22-2 to C Hm, the intensity of the M+l peak should be... 

Table 3.2 Abundance of isotopes for carbon, chlorine, and bromine...

Two or more atoms of the same element that contain different numbers of neutrons are said to be isotopes. An atom of a specific isotope is called a nuclide. Isotopes have similar chemical properties. Hydrogen has three important isotopes H (pro-tium), 2H (deuterium), and 3H tritium). 99.98% of naturally occurring hydrogen is protium. Examples of three isotopes for carbon are ... 

As shown in Table 14.1, is the most abundant isotope for carbon. For the chemical reactions discussed in this book, using 12.0107 for the atomic mass is appropriate. In mass spectrometry, molecules are separated based on mass, which means that isotopes are differentiated. For that reason, the exact mass or isotopic mass of each isotope must be used. The exact masses of the various isotopes are shown in Table 14.1. If the mass of a molecule is determined to be 100.1251, that ion will be composed of the most abundance, lowest mass isotopes for each atom H, etc. 

Atoms of many other elements contain nuclei that have different numbers of neutrons. For example, carbon (Z = 6) can have six neutrons (M = 6 + 6 = 12), seven neutrons (M = 13), or eight neutrons (M = 14). Atoms of the same atomic number but having different numbers of neutrons (and different atomic masses) are called isotopes. Thus, naturally occurring carbon has three isotopes, for which Z = P = 6 and N = 6 or 7 or 8. These are written. ... 

For any one element, the abundances (relative amounts) of isotopes can be described in percentage terms. Thus, fluorine is monoisotopic viz., it contains only nuclei of atomic mass 19, and phosphorus has 100% abundance of atoms with atomic mass 31. For carbon, the first two isotopes occur in the proportions of 98.882 to 1.108. 

For marble provenance studies, the most successful technique seems to be the measurement, through mass spectrometry, of the abundance ratios of the stable isotopes of carbon and oxygen (116). However, no single technique appears to provide unequivocal results, especially in cases such as the different Mediterranean sources, and a combination is often necessary to arrive at an approximate place of origin (117). 

Any radioactive nucUde or isotope of an element can be used as a radioactive tracer, eg, chromium-51 [14392-02-0] cobalt-60 [10198-40-0] tin-110 [15700-33-1] and mercury-203 [13982-78-0],hut the preponderance ofuse has been for carbon-14 [14762-75-5],hydj ogen-3 [10028-17-8] (tritium), sulfur-35 [15117-53-0], phosphoms-32, and iodine-125 [14158-31 -7]. More recendy phosphoms-33 has become available and is used to replace sulfur-35 and phosphoms-32 in many appUcations. By far the greater number of radioactive tracers produced are based on carbon-14 and hydrogen-3 because carbon and hydrogen exist in a large majority of the known natural and synthetic chemical compounds. 

To set up a scale of atomic masses, it is necessary to establish a standard value for one particular species. The modem atomic mass scale is based on the most common isotope of carbon, 1 C. This isotope is assigned a mass of exactly 12 atomic mass units (amu) ... 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

Craig, H. (1957a). Isotopic standards for carbon and correction factors for mass-spectrometric analysis of carbon dioxide. Geochim. Cosmochim. Acta 12, 133-149. 

We proposed to study diet and health by combining bone chemistry and histomorphometry. Diet would be determined by analysis of stable isotopes of carbon and nitrogen in bone protein and some preserved hair. In addition, trace elements would be quantitatively analyzed in preserved bone mineral. Abonyi (1993) participated in the study by reconstructing the diet from historical sources and analyzing various foods. Having analyzed human tissues for stable isotopes and trace elements, and foods for the same variables, we hoped to learn more about 19th century diet in southern Ontario, and at the same time, learn more about paleodiet reconstruction. 

Raw foods were freeze-dried and analyzed for carbon isotopes using mass spectrometry. Cooked foods were prepared following historic recipes, then were freeze-dried prior to analysis. For the trace element analysis, foods (both raw and cooked) were wet ashed using nitric acid in Teflon lined pressure vessels and digested in a CEM Microwave oven. Analysis of Sr, Zn, Fe, Ca and Mg was performed using Atomic Absorption Spectrometry in the Department of Geology, University of Calgary. 

Raw ingredients and cooked recipes were analyzed for stable isotopes of carbon (Abonyi 1993). To our knowledge, no one has determined if there are differences in the stable isotope values of raw and cooked foods, however Hastorf and DeNiro (1985) did compare plant remains that were heated to those that had not been heated. They found no significant difference in isotope values due to heating. Marino and DeNiro (1987) studied the effects ofheating (boiling and roasting) on several types of plants to determine if cellulose... 

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. 

Isotopic variation in European human remains is caused by a combination of environmental, biological and cultural factors. For carbon, the main influence is the dominance of C3 photosynthesis in all vegetation types. The factors that can cause deviations from this general trend are the climatic effect,... 

Bottinga, Y. 1969 Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapour. Geochimica et CosmochimicaActa 33 49-64. 

As for carbonate measurements, the model confirms that bioapatite-carbonate should exhibit a 8 C value offset from the average-ingested-diet by an amount equal to the isotopic equilibrium fractionation between carbonate and gaseous CO2. 

Carnivores rely on a protein-rich diet and produce new biomass primarily from dietary amino acids, although the enzymes required for de novo amino acid synthesis are present (Garmes et al., 1998). Bone collagen, muscle (meat) and apatite were analyzed for a set of modern southern African herbivores and carnivores (Lee-Thorp et al., 1989). The isotopic analyses showed i C enrichment in bone collagen, apatite and muscle, and depletion in lipids. Difference in values between herbivores and carnivores indicates a trophic effect, which for carbon in bone collagen is 2.5-3%o (Fig. 2). 

Rau, G.H. (1982). The relationship between trophic level and stable isotopes of carbon and nitrogen. In Coastal water research project biennial report for the years 1981-1982. Edited by W. Bascom. Southern California Water Research Project, Long Beach, Calif, pp. 143-148. 

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