Carbon stable isotope ratio test

More recently, the carbon stable isotope ratio test (SIRA) has become an easy method to detect adulteration with cane and corn syrup (Carro et al, 1980). Because maple trees are C3 plants with a somewhat different photosynthetic pathway for carbon fixation, the ratio of 13C/12C in the sugar produced is different than cane or com. Maple has a 813C of approximately —24.5, whereas com and cane are closer to a 813C of —8 to —12. Thus, even a small addition of cane or corn syrup is readily detectable. Because beets are also C3 plants, the SIRA test is not able to detect adulteration with beet sugar. Improvement of the SIRA method is possible using malic acid as an internal standard (Tremblay and Paquin, 2007). 

Much of what is currently understood about the Cenozoic history, of deep-sea temperature, carbon chemistry, and global ice volume, has been gleaned from the stable isotope ratios of benthic foraminifera. Benthic foraminifera extract carbonate and other ions from seawater to construct their tests. In many species, this is achieved near carbon and oxygen isotopic equilibrium. Kinetic fractionation effects tend to be small and constant (Grossman, 1984, 1987). As a result, shell fi C and strongly covary with the isotopic... 

Aliquots of CO2 produced during 0-plasmas were analyzed on three different stable isotope-ratio mass spectrometers over a period of five years. The peyote button and the T-shirt label were both run in the summer of 2001. These two samples were chosen to further establish that mass fractionation of carbon during the oxygen plasmas is a small or negligible effect and to test the nondestructive nature of the technique on organic materials. For calibration to Peedee belemnite (PDB) primary standard, carbonate standard NBS-19 (8 C = 1.95%o) was used (i.e., Vienna PDB). values are expressed relative to the V-PDB standard (19). Analytical precision was approximately 0.06%o for 6 C. 

Oxygen exists as three stable isotopes, 160,170 and 180 (see Box 1.3 and Table 1.1), all of which are present in the water of the oceans and so take part in the equilibrium reaction involving carbonate shown in Eqn 3.8. Organisms that secrete calcium carbonate tests incorporate the isotopes of oxygen broadly in the ratio in which they occur in ambient seawater, although there is also an isotopic fractionation, which varies with temperature (the colder the water, the greater is the proportion of 180 relative to 160) and species. The ratio of the two most abundant isotopes can be expressed by ... 

The stable carbon isotope signal preserved in benthic foraminiferal carbonate tests reflects global ocean circulation and organic carbon fluxes. It is also subject to local influences, notably gradients in the isotope ratios of sediment pore-waters ( microhabitat effect ), and vital effects possibly related to the incorporation of metabolic carbon into the shell material (McCorkle et al. 1990 Mackensen Bickert 1999 Schmiedl et al. 2004). Mackensen et al. (1993) recogiuzed a ph)4odetritus effect whereby deviations in 8 C... 

Much use is made of the stable isotopes of carbon as a paleo-water mass isotope fingerprint . The ratio in the tests of foraminifera depends on the relative position of the overlying water mass within the thermohaline circulation system. Flowever, these isotope ratios are modified during the incorporation into organisms, depend on availability of nutrients, and like the isotopes of oxygen, also depend on seawater temperature. (These tracers are dealt with in the relevant articles please refer to the See also section.)... 

Accelerator mass spectrometry (AMS) is useful to measure extremely low-abundance nuclides (isotope ratio of 10 to 10 relative to its stable isotope), such as Be, C, A1, C1, " Ca, and I, in natural samples. Small amounts of C and T can be measured by AMS on mg size samples of carbon and iodine extracted from 500-ml seawater samples (Povinec et al. 2000). Neutron activation analysis (NAA), radiochemical neutron activation analysis (RNAA), and inductively coupled plasma mass spectrometry (ICP-MS) are useful for the determination of ultra-trace Th and U in geological and cosmochemical samples, and for determination of the concentration of Pu and Pu. Reference marine-biological samples are necessary to test the performance of the analytical methods employed in surveying and monitoring radioactive materials in the sea. An ocean shellfish composite material containing 0.1% w/w Irish Sea mussel, 12% w/w White Sea mussel, and 87.9% w/w Japan Sea oyster has been prepared as the NIST SRM 4358 (The National Institute of Standards and Technology, SRM) in the natural-matrix, environmental-level radioactive SRM series (Altzitzoglou 2000). This NIST SRM 4358 sample will be useful for the determination of the activity of K, Cs, Pb, Ra, Th, and Am. 

Due to the uncertainty of the relative amount of oxalate present, the entire remaining sample (- SbO mg) was treated at Arkansas State University for the AMS and stable carbon isotope ratio (5 C) analyses to maximize the probability that sufficient oxalate would be present for viable results. To remove carbonates, the powdered sample was placed in a Teflon beaker and treated with 25 ml of dilute phosphoric acid. After the initial acid/carbonate effervescence ceased, the pH of the solution was adjusted to pH 2 using concentrated phosphoric acid. This pH was maintained for several days to ensure all carbonates were removed. This phosphoric acid treatment was tested and reported in Russ et al. (25), A final FTIR analysis established the removal of carbonate by the disappearance of the strong absorption peak at 1405 cm and also confirmed the presence of oxalate with absorption peaks at 1618 and 1315 cm . The remaining sample was divided into two aliquots with approximately half sent to The University of Arizona AMS facility for " C analysis and the remaining half to T. W. Boutton at Texas A M for the 6 C measurement. 

Based on these results, it is clear that g values can be used to reconstruct the thermal history of burned bones, and that correction factors can be developed to back correct for the effects of thermal alteration on stable carbon- and nitrogen-isotope ratios. Further experiments are needed on charred and uncharred bones from prehistoric sites to test the accuracy of back corrections in prehistoric cremated bones. 

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