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Stable isotope ratio

  (Redirected from Isotope ratio)

The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundance of such stable isotopes can be measured experimentally (isotope analysis), yielding an isotope ratio that can be used as a research tool. Theoretically, such stable isotopes could include the radiogenic daughter products of radioactive decay, used in radiometric dating. However, the expression stable-isotope ratio is preferably used to refer to isotopes whose relative abundances are affected by isotope fractionation in nature. This field is termed stable isotope geochemistry.

Stable-isotope ratiosEdit

Measurement of the ratios of naturally occurring stable isotopes (isotope analysis) plays an important role in isotope geochemistry, but stable isotopes (mostly carbon, nitrogen, oxygen and sulfur) are also finding uses in ecological and biological studies. Other workers have used oxygen isotope ratios to reconstruct historical atmospheric temperatures, making them important tools for paleoclimatology.

These isotope systems for lighter elements that exhibit more than one primordial isotope for each element, have been under investigation for many years in order to study processes of isotope fractionation in natural systems. The long history of study of these elements is in part because the proportions of stable isotopes in these light and volatile elements is relatively easy to measure. However, recent advances in isotope ratio mass spectrometry (i.e. multiple-collector inductively coupled plasma mass spectrometry) now enable the measurement of isotope ratios in heavier stable elements, such as iron, copper, zinc, molybdenum, etc.


The variations in oxygen and hydrogen isotope ratios have applications in hydrology since most samples will lie between two extremes, ocean water and Arctic/Antarctic snow.[1] Given a sample of water from an aquifer, and a sufficiently sensitive tool to measure the variation in the isotopic ratio of hydrogen in the sample, it is possible to infer the source, be it ocean water seeping into the aquifer or precipitation seeping into the aquifer, and even to estimate the proportions from each source.[2] Stable isotopes of water are also used in partitioning water sources for plant transpiration and groundwater recharge.[3][4]

Another application is in paleotemperature measurement for paleoclimatology. For example, one technique is based on the variation in isotopic fractionation of oxygen by biological systems with temperature.[5] Species of Foraminifera incorporate oxygen as calcium carbonate in their shells. The ratio of the oxygen isotopes oxygen-16 and oxygen-18 incorporated into the calcium carbonate varies with temperature and the oxygen isotopic composition of the water. This oxygen remains "fixed" in the calcium carbonate when the forminifera dies, falls to the sea bed, and its shell becomes part of the sediment. It is possible to select standard species of forminifera from sections through the sediment column, and by mapping the variation in oxygen isotopic ratio, deduce the temperature that the Forminifera encountered during life if changes in the oxygen isotopic composition of the water can be constrained.[6] Paleotemperature relationships have also enabled isotope ratios from calcium carbonate in barnacle shells to be used to infer the movement and home foraging areas of the sea turtles and whales on which some barnacles grow.[7]

In ecology, carbon and nitrogen isotope ratios are widely used to determine the broad diets of many free-ranging animals. They have been used to determine the broad diets of seabirds, and to identify the geographical areas where individuals spend the breeding and non-breeding season.[8] Numerous ecological studies have also used isotope analyses to understand migration, food-web structure, diet, and resource use in sea turtles[9]. Determining diets of aquatic animals using stable isotopes has been particularly common, as direct observations are difficult[10], they also enable researchers to measure how human interactions with wildlife, such as fishing, may alter natural diets[11].

In forensic science, research suggests that the variation in certain isotope ratios in drugs derived from plant sources (cannabis, cocaine) can be used to determine the drug's continent of origin.[12]

In food science it has been used to determine the composition of beer,[13] shoyu sauce[14] and dog food.[15]

It also has applications in "doping control", to distinguish between endogenous and exogenous (synthetic) sources of hormones.[16][17]

Chondrite meteorites are classified using the oxygen isotope ratios. In addition, an unusual signature of carbon-13 confirms the non-terrestrial origin for organic compounds found in carbonaceous chondrites, as in the Murchison meteorite.

See alsoEdit



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  4. ^ Evaristo, Jaivime; Jasechko, Scott; McDonnell, Jeffrey J. (2015). "Global separation of plant transpiration from groundwater and streamflow". Nature. 525 (7567): 91–94. Bibcode:2015Natur.525...91E. doi:10.1038/nature14983. PMID 26333467.
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  6. ^ Shen JJ, You CF (2003). "A 10-fold improvement in the precision of boron isotopic analysis by negative thermal ionization mass spectrometry". Anal. Chem. 75 (9): 1972–7. doi:10.1021/ac020589f. PMID 12720329.
  7. ^ Pearson, Ryan M.; van de Merwe, Jason P.; Gagan, Michael K.; Limpus, Colin J.; Connolly, Rod M. (2019). "Distinguishing between sea turtle foraging areas using stable isotopes from commensal barnacle shells". Scientific Reports. 9 (1): 6565. doi:10.1038/s41598-019-42983-4. ISSN 2045-2322.
  8. ^ Graña Grilli, M.; Cherel, Y. (2017). "Skuas (Stercorarius spp.) moult body feathers during both the breeding and inter-breeding periods: implications for stable isotope investigations in seabirds". Ibis. 159 (2): 266–271. doi:10.1111/ibi.12441. Italic or bold markup not allowed in: |journal= (help)
  9. ^ Pearson, RM; van de Merwe, JP; Limpus, CJ; Connolly, RM (2017). "Realignment of sea turtle isotope studies needed to match conservation priorities". Marine Ecology Progress Series. 583: 259–271. Bibcode:2017MEPS..583..259P. doi:10.3354/meps12353. ISSN 0171-8630.
  10. ^ Gutmann Roberts, Catherine; Britton, J. Robert (2018-09-01). "Trophic interactions in a lowland river fish community invaded by European barbel Barbus barbus (Actinopterygii, Cyprinidae)". Hydrobiologia. 819 (1): 259–273. doi:10.1007/s10750-018-3644-6. ISSN 1573-5117.
  11. ^ Gutmann Roberts, Catherine; Bašić, Tea; Trigo, Fatima Amat; Britton, J. Robert (2017). "Trophic consequences for riverine cyprinid fishes of angler subsidies based on marine-derived nutrients" (PDF). Freshwater Biology. 62 (5): 894–905. doi:10.1111/fwb.12910. ISSN 1365-2427.
  12. ^ Casale J, Casale E, Collins M, Morello D, Cathapermal S, Panicker S (2006). "Stable isotope analyses of heroin seized from the merchant vessel Pong Su". J. Forensic Sci. 51 (3): 603–6. doi:10.1111/j.1556-4029.2006.00123.x. PMID 16696708.
  13. ^ Brooks, J. Renée; Buchmann, Nina; Phillips, Sue; Ehleringer, Bruce; Evans, R. David; Lott, Mike; Martinelli, Luiz A.; Pockman, William T.; Sandquist, Darren; Sparks, Jed P.; Sperry, Lynda; Williams, Dave; Ehleringer, James R. (October 2002). "Heavy and Light Beer:  A Carbon Isotope Approach To Detect C4 Carbon in Beers of Different Origins, Styles, and Prices". Journal of Agricultural and Food Chemistry. 50 (22): 6413–6418. doi:10.1021/jf020594k. PMID 12381126.
  14. ^ Morais, M.C.; Pellegrinetti, T.A.; Sturion, L.C.; Sattolo, T.M.S.; Martinelli, L.A. (February 2019). "Stable carbon isotopic composition indicates large presence of maize in Brazilian soy sauces (shoyu)". Journal of Food Composition and Analysis. doi:10.1016/j.jfca.2019.01.020.
  15. ^ Galera, Leonardo de Aro; Abdalla Filho, Adibe Luiz; Reis, Luiza Santos; Souza, Janaina Leite de; Hernandez, Yeleine Almoza; Martinelli, Luiz Antonio (20 February 2019). "Carbon and nitrogen isotopic composition of commercial dog food in Brazil". PeerJ. 7: e5828. doi:10.7717/peerj.5828. PMC 6387582. PMID 30809425.
  16. ^ Author, A (2012). "Stable isotope ratio analysis in sports anti-doping". Drug Testing and Analysis. 4 (12): 893–896. doi:10.1002/dta.1399. PMID 22972693.
  17. ^ Cawley, Adam T.; Kazlauskas, Rymantas; Trout, Graham J.; Rogerson, Jill H.; George, Adrian V. (1985). "Isotopic Fractionation of Endogenous Anabolic Androgenic Steroids and Its Relationship to Doping Control in Sports". Journal of Chromatographic Science. 43: 32–38. Bibcode:1985JChS...23..471O. doi:10.1093/chromsci/43.1.32.