12C/13C ratios

Grinsted, M. J. and A. T. Wilson (1979), Variations of 13C/12C ratio in cellulose of Agathus australis (Kauri) and climatic change in New Zealand during the last millennium, New Zealand. Sci. 22, 55-61. 

A 13C/12C ratio about 3% above that of a standard value (the so-called VPDB standard) had been found in western Australian rock samples from the Pilbara Formation similar values were found for the Isua rock. However, since this no longer had its original morphology, the yeast-like relicts found by Pflug (1978) may not be real, and doubts have been cast, in particular by the American scientists J. W. Schopf andE. Roedder (Breuer, 1981,1982). Neither the Isua microfossils nor their 13C/12C isotope ratio could convince Bill Schopf that 3.8-billion-year-old samples were really involved. The Isua graphite flakes could also be a charred residuum from the... 

The chemical analysis has revealed that rather low C/O ratios are found in metal-poor extragalactic carbon stars, as found for galactic carbon stars of the solar vicinity. Furthermore, the three analyzed stars show similar s-elements enhancements [ls/Fe]=0.8-1.3 and [hs/Fe]=l.l-1.7. This leads to new constraints for evolutionary models. For instance, the derived C/O and 13C/12C ratios are lower than model predictions at low metallicity. On the contrary, theoretical predictions of neutrons exposures for the production of the s-elements are compatible with observations (see Fig. 1). Finally, from their known distances, we have estimated the luminosities and masses of the three stars. It results that SMC-B30 and Sgr-C3 are most probably intrinsic carbon stars while Sgr-Cl could be extrinsic. 

Hener, U., Brand, W. A., Hilkert, A. W., Juchelka, D., Mosandl, A. and Podebrad, F. (1998) Simultaneous online analysis of 180/160 and 13C/12C ratios of organic compounds using GC pyrolysis IRMS. Zeitschrift fur Lebensmittel Untersuchung und Forschung 206, 230 232. 

Methods for pretreatment of samples for 13C analysis had been described in Chen et al. (2002a). After pretreatment, soil samples and plant debris were sent to the State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (CAS), for 13C analyses. The 13C analyses were conducted using a Finnigan MAT-251 mass spectrometer manufactured by Finnigan-Mat Company, with a precision of 0.2%o. Results are reported as 513C, in parts per thousand of the 13C/12C ratio from that of the International Pee Dee belemnite (PDB) standard, where ... 

Evidence is accumulating which shows that materials isolated from the marine environment are quite unlike those isolated from soils, at least in 13C/12C ratios and probably in structure. 

As partly mentioned before, natural and anthropogenic induced variations of the atmospheric C02 concentration and of the 14C/ 12C and 13C/12C ratios have been observed. For a quantitative discussion of these variations in relation to possible causes, models for the carbon cycle dynamics have been developed [21-25]. Compared to the noble gas radioisotopes 39Ar and 81Kr, for which we only have to consider a well mixed atmospheric reservoir, we have a much more complicated system for 14C. The C02 in the atmosphere exchanges with the carbon in the biosphere and with the... 

Parallel (multidimensional) measurements of size- or chemically selected particles permit the simultaneous resolution of biogenic material from fossil sources (14C), discrimination between certain fossil sources and between marine and terrestrial vegetation (13C), and partial separation of agricultural burning sources (K/Fe). The term iMu represents the fraction of modern C based on standard Slk 813C represents the deviation (per mil) of the 13C/12C ratio from standard Sls (2). 

Because isotopic changes caused by chemical processes are so small, the isotopic data are typically reported as deviations in parts per thousand from a standard composition. For example, the shift in the 13C/12C ratio relative to a standard is given in delta notation by ... 

There are limitations beyond the difficulty of measuring small peaks The 13C/12C ratio differs with the source of the compound—synthetic compared with a natural source. A natural product from different organisms or regions may show differences. Furthermore, isotope peaks may be more intense than the calculated value because of ion-molecule interactions that vary with the sample concentration or with the class of compound involved. For example ... 

C/12C ratio in natural vanillin is smaller than that observed in synthetic vanillin. The same effect applies to glucose, whose isotopic carbon distribution varies depending on the biological cycle of the plant. 

To learn whether people from the ancient British coastal town of Barton-on-Humber ate mainly plants or fish, cholesterol from the bones of 50 people was extracted with organic solvent, isolated by gas chromatography, combusted to convert it into COz, and its 13C/I2C ratio measured by mass spectrometry. Observed 13C/12C ratios differ from that of a standard material by about —21 to —24 parts per thousand. A diet of local plants yields a 5I3C value (defined in Box 22-3) in cholesterol of —28 parts per thousand. Values more positive than —28 parts per thousand are indicative of a marine diet. It appears that the population got much of its food from the sea. 

With the 12CO-13CO mixture, 13CO radicals would give two triplets centered around the 12CO triplet, and the intensity ratio should be equal to the 13C/12C ratio this was not observed (Figure 4). 

Carbon-isotopic (13C/12C) ratios of the combustible organic matter fluctuate, but these variations can be correlated with warm (interglacial) and cold (glacial) periods of the Pleistocene (3). 

More recently, enantiomer ratios have been used as evidence of adulteration in natural foods and essential oils. If the enantiomer distribution of achiral component of a natural food does not agree with that of a questionable sample, then adulteration can be suspected. Chiral GC analysis alone may not provide adequate evidence of adulteration, so it is often used in conjunction with other instrumental methods to completely authenticate the source of a natural food. These methods include isotope ratio mass spectrometry (IRMS), which determines an overall 13C/12C ratio (Mosandl, 1995), and site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy (SNIF-NMR), which determines a 2H/ H ratio at different sites in a molecule (Martin et al 1993), which have largely replaced more traditional analytical methods using GC, GC-MS, and HPLC. 

Authenticity evaluation has recently received increased attention in a number of industries. The complex mixtures involved often require very high resolution analyses and, in the case of determining the authenticity of natural products, very accurate determination of enantiomeric purity. Juchelka et al. have described a method for the authenticity determination of natural products which uses a combination of enantioselective multidimensional gas chromatography with isotope ratio mass spectrometry (28). In isotope ratio mass spectrometry, combustion analysis is combined with mass spectrometry, and the 13C/12C ratio of the analyte is measured versus a C02 reference standard. A special interface, employing the necessary oxidation and reduction reaction chambers and a water separator, was used employed. For standards of 5-nonanone, menthol and (R)-y-decalactone, they were able to determine the correct 12C/13C ratios, with relatively little sample preparation. The technical details of multidimensional GC-isotope ratio MS have been described fully by Nitz et al. (29). A MDGC-IRMS separation of a natural ds-3-hexen-l-ol fraction is... 

Fry, G., 1989. 13c/12c ratios and the trophic importance of algae in Florida Syringodium filiforme seagrass meadows. Mar. Biol., 79 11-19. 

It appears clearly from Fig. 1 that the mean value of 813C characteristic of total carbon has no meaning in terms of isotopic signatures. The value of 8 varies from one class of molecules to another, going from positive values (—I- 30 %) for aminoadds to negative values for the more reduced hydrocarbons. Moreover, the 13C/12C ratio for individual hydrocarbons and monocarboxylic acids decreases with... 

This 13C/12C ratio difference between carbon at different levels of oxidation now brings us to a brief discussion of a problem already discussed 40 years ago by Urey83) in relation to carbon compounds of geological interest (C03, C02, CO, diamond) and extended by Craig 84) to the CH4 case. These authors studied the equilibration between isotopomers like... 

Keeling C.D., Bacastrow R.D. and Tans P.P. (1980) Predicted shift in the 13C/12C ratio of atmospheric carbon dioxide. Geophys. Res. Lett. 7, 505-508. 

Previous studies using l C and 13c/12c measurements in connection with other source apportionment techniques have demonstrated their value in assessing the importance of various sources (3). In winter studies in Portland, OR, at a site in which the impact from wood-burning is large, the fraction of contemporary carbon was near 100% urban plume values of l C for Denver samples were substantially lower (10-5A% contemporary) (8). Previous values reported for Long Island, NY, and Barrow, AK, sites were in the range of 30% contemporary carbon (5), with 13c/12c ratios consistent with a combination of fossil fuel and C-3 plant biogenic sources ( 13c ---26). 

Abrajano, Jr., T.A., Murphy, D.E., Fang, J. Comet, P., Brooks, J.M. (1994) 13C/12C ratios in individual fatty acids of marine mytilids with and without bacterial symbionts. Org. Geochem. 21, 611-617. 

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