- Isotopic signature
An isotopic signature (also isotopic fingerprint) is a ratio of stable or unstable
isotopes of particular elements found in an investigated material. The atomic massof different isotopes affect their chemical kinetic behavior, leading to natural isotope separationprocesses.
For example, different sources and sinks of
methanehave different affinity for the 12C and 13C isotopes, which allows distinguishing between different sources by the 13C/12C ratio in methane in the air.
Similarly, carbon in inorganic
carbonates shows little isotopic fractionation, while carbon in materials originated by photosynthesisis depleted of the heavier isotopes. In addition, there are two types of plants with different biochemical pathways; the C3 carbon fixation, where the isotope separation effect is more pronounced, and C4 carbon fixation, where the heavier 13C is less depleted. The different isotope ratios for the two kinds of plants propagate through the food chain, thus it is possible to determine if the principal diet of a human or an animal consists primarily of C3 plants ( rice, wheat, soybeans, potatoes) or C4 plants (corn, or corn-fed beef) by isotope analysisof their flesh and bone collagen. Similarly, marine fish contain more 13C than freshwater fish, with values approximating the C4 and C3 plants respectively. Limestones formed by precipitation in seas from the atmospheric carbon dioxide contain normal proportion of 13C. Conversely, calcitefound in salt domes originates from carbon dioxide formed by oxidation of petroleum, which due to its plant origin is 13C-depleted.
The 14C isotope is important in distinguishing biosynthetized materials from man-made ones. Biogenic chemicals are derived from biospheric carbon, which contains 14C. Carbon in artificially made chemicals is usually derived from
fossil fuels like coalor petroleum, where the 14C originally present has decayed below detectable limits. The amount of 14C currently present in a sample therefore indicates the proportion of carbon of biogenic origin.
The ratio of 15N/14N presents a characteristic distinction between
herbivores and carnivores, as the movement up along the food chain tends to concentrate the 15N isotope, by 3-4‰ with each step of the food chain (terrestrial plants, with the exception of legumes, has the isotopic ratio 2-6‰ of N). The tissues and hairof vegans therefore contain significantly lower percentage of 15N than the bodies of people who eat mostly meat. Isotopic analysis of hair is an important source of information for archaeologists, providing clues about the ancient diets; a terrestrial diet produces a different signature than a marine-based diet and this phenomenon has been used in analysing differing cultural attitudes to food sources.
Oxygen comes in two variants as well. The ratio of 18O/16O in water depends on the amount of evaporation the water experienced (as 18O is heavier and therefore less likely to vaporize). As the vapor tension depends on the concentration of dissolved salts, the 18O/16O ratio shows correlation on the salinity and temperature of water. As oxygen gets built into the shells of
calcium carbonatesecreting organisms, such sediments prove a chronological record of temperature and salinity of the water in the area.
Hot particles, radioactive particles of nuclear falloutand radioactive waste, also exhibit distinct isotopic signatures. Their radionuclide composition (and thus their age and origin) can be determined by mass spectroscopyor by gamma spectrometry. For example, particles generated by a nuclear blast contain detectable amounts of 60Co and 152Eu. The Chernobyl accidentdid not release these particles but did release 125Sb and 144Ce. Particles from underwater bursts will consist mostly of irradiated sea salts. Ratios of 152Eu/155Eu, 154Eu/155Eu, and 238Pu/239Pu are also different for fusion and fission nuclear weapons, which allows identification of hot particles of unknown origin.
With the advent of stable
isotope ratio mass spectrometry, isotopic signatures of materials find increasing use in forensics, allowing disguising the origin of otherwise similar materials and tracking the materials to their common source. For example the isotope signatures of plants can be to a degree influenced by the growth conditions, including moisture and nutrient availability. In case of synthetic materials, the signature is influenced by the conditions during the chemical reaction. The isotopic signature profiling is useful in cases where other kinds of profiling, eg. characterization of impurities, are not optimal.
A study was published demonstrating the possibility of determination of the origin of a common brown PSA packaging tape by using the carbon, oxygen, and hydrogen isotopic signature of the backing polymer, additives, and adhesive [http://www.rsc.org/publishing/journals/AN/article.asp?doi=b409341k] .
* [http://ethomas.web.wesleyan.edu/ees123/carboniso.htm Carbon isotopes: you are what you eat]
* [http://www.evsc.virginia.edu/news/esreport99/hair.htm Hair-rising research]
* [http://brian.finucane.googlepages.com/ayacuchoarchaeo-isotopeproject Ayacucho Archaeo Isotope Project]
* [http://www.radiocarbon.org/Subscribers/Fulltext/v40n1-2_Currie_381.html The pursuit of isotopic and molecular fire tracers in the polar atmosphere and cryosphere]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Isotopic labeling — (or isotopic labelling) is a technique for tracking the passage of a sample of substance through a system. The substance is labeled by including unusual isotopes in its chemical composition. If these unusual isotopes are later detected in a… … Wikipedia
Signature (disambiguation) — A signature is a hand written, stylized version of someone s name.Signature may also mean: NOTOC In computers*Signature block, text automatically appended at the bottom of an e mail message, Usenet article, or forum post. *Method signature, in… … Wikipedia
Presolar grains — are isotopically distinct clusters of material found in the fine grained matrix of primitive meteorites, whose differences from the surrounding meteorite suggest that they are older than the solar system [Maria Lugaro (2005) Stardust from… … Wikipedia
Magmatic water — or juvenile water is water which exists within and in equilibrium with a magma or water rich volatile fluids which are derived from a magma. This magmatic water is released to the atmosphere during a volcanic eruption. Magmatic water may also be… … Wikipedia
Isotope — This article is about the atomic variants of chemical elements. For the British jazz fusion band, see Isotope (band). Isotopes redirects here. For the minor league baseball team, see Albuquerque Isotopes. Isotopes are variants of atoms of a… … Wikipedia
dating — I In geology and archaeology, the process of determining an object s or event s place within a chronological scheme. Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy) or … Universalium
Giant impact hypothesis — Big splash redirects here. For other uses, see Big Splash (disambiguation). Artist s depiction of the giant impact that is hypothesized to have formed the Moon The giant impact hypothesis proposes that the Moon was created out of the debris left… … Wikipedia
Isotope analysis — is the identification of isotopic signature, the distribution of certain stable isotopes and chemical elements within chemical compounds. This can be applied to a food web to make it possible to draw direct inferences regarding diet, trophic… … Wikipedia
hydrosphere — /huy dreuh sfear /, n. the water on or surrounding the surface of the globe, including the water of the oceans and the water in the atmosphere. [1885 90; HYDRO 1 + SPHERE] * * * Discontinuous layer of water at or near the Earth s surface. It… … Universalium
Crustal recycling — Understanding predictions of mantle dynamics helps geoscientists predict where subducted crust will end up. Crustal recycling is a tectonic process by which surface material from the lithosphere is recycled into the mantle during subduction. The… … Wikipedia