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... 

In this description of the geochemistry of formation water, we will consider first the distribution of Na, Cl and SOV ions which are some of the most dominant major-ion species and second the stable-isotope ratios of D/H and O/ O. The basic data for the ion chemistry come from a set of 240 good-quality unpublished analyses of samples collected mainly from drill-stem tests but some from separators. These data are supplemented by 1500 analyses of formation water gathered over the last 20 years by the... 

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. 

These techniques have been used in forensic science to identify murder victims. For example, in Ireland, the headless body of a male 35-40 years old was discovered. Skin color and physical characteristics suggested that he was of African/Afro-Caribbean or African-American ancestry. Stable isotope ratios in his hair, bones, and teeth were compared with those of people whose geographic origin and life history were known. From the hair, it was established that he had lived in Ireland for at least 9-12 months before his death. The femur was then tested while ribs remodel in about 10 years, long bones such as the femur take about 20 years. The inner part of the bone reflects the most recent history, and the 0/ 0 profile corresponded to local drinking water. However, the outer, older part of the femur suggested water with a 8 value of... 

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.)... 

Inglett, P. W., K. R. Reddy, S. Newman, and B. Lorenzen. 2007. Increased soil stable nitrogen isotopic ratio following phosphorus enrichment historical patterns and tests of two hypotheses in a phosphorus-limited wetland. Oecologia. Online reference 10.1007/s00442-007-0711-5. 

For some radionuclides, only the direct measurement is needed, based on calibration with a radionuclide standard and reference to the measured sample mass. For other radionuclides, the isotope ratio to its stable element is needed. An example of a more complex situation is measurement of the 14C/12C isotope ratio of an environmental or archeological sample in comparison to the modern atmospheric CO2 value. This value must be adjusted for anthropogenic 14C produced by atmospheric testing of nuclear weapons and by other nuclear operations, and also for changes in atmospheric CO2 with cosmic-ray flux fluctuations over time. For an element such as Pu, which has no stable isotope, the total quantity is measured by isotope dilution mass spectrometry in which the sample is traced (or spiked) with 242Pu or 244Pu (see Section 17.3.3). 

The bioavailability of iron from meals based on corn tortillas and black bean paste fortified with iron(ll)fumarate with and without disodium EDTA, iron(ll) sulfate or sodium iron EDTA (as derived from mixing iron(lll) chloride with disodium EDTA in a 1 1 molar ratio of iron to disodium EDTA) was measured in a crossover study with 33 healthy Guatemalan girls (aged 12-13 years and weighing maximally 45 kg) via a stable isotope technique based on erythrocyte incorporation. The test... 

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