Using carbon isotopes

Carbon has two stable isotopes with the following abundances  

Measurements are made relative to a standard belemnite sample known as FDB — belemnitella americana from the Cretaceous Peedee formation. South Carolina. This standard is used because its and values are close to those of average marine 

Carbon isotopes are measured as CO2 gas and precision is normally better than 0.1 /ai. The CO2 Is liberated from carbonates with 103 % phosphoric acid or by thermal decomposition. Organic compounds are normally oxidized at very high tempe ratures in a stream of oxygen or with an oxidizing agent such as CuO. 

Controls on the The fractionation of carbon isotopes is controlled by both eguilibrium and kinetic 

Natural reservoirs. The ranges of 5 C values in natural, carbon-bearing samples. Data from Kerridge (198S), Exley et ai (1986), Field and Flfarek (1986), Hoefs (1987) and 

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To extend the study of the apparent decomposition recombination reaction, and specifically to determine if the carbon atoms exchange with other atoms in other acetylene molecules, tests using carbon isotopes were conducted. A mixture of 50% regular acetylene, C2H2, and 50% heavy acetylene. 

The amounts of the standard isotopic species and the tracer isotopic species are represented by X and X for the sample and the reference material. The reference substance is chosen arbitrarily, but is a substance that is homogeneous, available in reasonably large amounts, and measurable using standard analytical techniques for measuring isotopes (generally mass spectrometry). For instance, a sample of ocean water known as Standard Mean Ocean Water (SMOW) is used as a reference for and 0. Calcium carbonate from the Peedee sedimentary formation in North Carolina, USA (PDB) is used for C. More information about using carbon isotopes is presented in Chapter 11. 

Ceding, T.E. (1992a) Further comments on using carbon isotopes in paleosols to estimate the CO2 content of the paleo-atmosphere. J. Geol. Soc. London, 149, 673-676. 

The most widely used standard is a belemnite from the Peedee Formation in South Carolina (PDB) therefore, some ratios may be expressed as negative values. Most carbon isotope ratio correlations are made on the C15+ fraction of crude oil because it is less affected by degradation processes. Valid correlations using carbon isotopes can only be conducted on the same fractions of samples. 

Scientists commoniy use the isotope carbon-14 as a tooi to determine the age of objects composed of materiai that was once aiive. Determining the age of something using carbon isotopes is caiied carbon dating, or radiocarbon dating. 

Aravena R., Schiff S. L., Tmmbore S. E., Dillon P. J., and Elgood R. (1992) Evaluating dissolved inorganic carbon cycling in a forested lake watershed using carbon isotopes. Radiocarbon 34(3), 636—645. 

Most of the paleodiet work using carbon isotopes has focused on the organic collagen in bone. Carbon also is found in the mineral, or carbonate, portion of bone and tooth enamel and contains information on diet. Although there are potential problems with contamination, this information can provide additional insight on questions regarding diet and place of origin of the individual from whom the sample was taken. 

The situation is even more difficult with respect to current knowledge of the carbon-isotope composition of the SOC pool. Work in this area with few exceptions (e.g.. Bird et al., 1996 Bird and Pousai, 1997) has focused on using carbon isotopes as a tracer of carbon dynamics and vegetation change in local regions. There is an urgent need for techniques that can be used to provide observational estimates of the carbon-isotope composition of the SOC pool and of carbon fluxes from the SOC pool to the atmosphere. 

Finally, researchers have perfected techniques of using carbon isotope ratios to identify unnatural molecules of otherwise natural compounds. This ability has led to the detection of synthetic testosterone in several athletes. In 2006, American Floyd Landis took over where Lance Armstrong left off, winning the Tour de France after the former champion s retirement. Unfortunately, after stage 17, Landis tested positive for an elevated ratio of testosterone to its precursor epitestosterone. Subsequent tests of carbon isotope ratios showed that the samples contained synthetic testosterone. 

Rahman, O., Langstrom, B., Kihlberg, T., Llop, J. 2005. Methods for carbon isotope labeling synthesis of ketones and amines by Suzuki coupling reactions using carbon- isotope monoxide. PCT Int. Appl. 

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