Isotope fractionation
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Isotope fractionation describes fractionation processes that affect the relative abundance of isotopes, a phenomena that occurs (and so advantage is taken of it) in the study geochemistry,[1] biochemistry,[2] food science,[3] and other fields. Normally, the focus is on stable isotopes of the same element. Isotopic fractionation can be measured by isotope analysis, using isotope-ratio mass spectrometry,[1] nuclear magnetic resonance methods (specialised techniques,[2][3]) cavity ring-down spectroscopy,Template:Citation needed lead etc., to measure ratios of isotopes, important tools to understand geochemical and biological systems, past and present.Template:Citation needed lead For example, biochemical processes cause changes in ratios of stable carbon isotopes incorporated into biomass.Template:Citation needed lead
Definition
Stable isotopes partitioning between two substances A and B can be expressed by the use of the isotopic fractionation factor (alpha):
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where R is the ratio of the heavy to light isotope (e.g., 2H/1H or 18O/16O). Values for alpha tend to be very close to 1.[1][4]
Types
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Example
Isotope fractionation occurs during a phase transition, when the ratio of light to heavy isotopes in the involved molecules changes. As Carol Kendall of the USGS states in an information page for the USGS Isotope Tracers Project, "water vapor condenses (an equilibrium process), the heavier water isotopes (18O and 2H) become enriched in the liquid phase while the lighter isotopes (16O and 1H) tend toward the vapor phase".[1]
See also
References
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Further reading
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- Faure G., Mensing T.M. (2004), "Isotopes: Principles and Applications", (John Wiley).Template:Full
- Hoefs J. (2004), "Stable Isotope Geochemistry", (Springer Verlag).Template:Full
- Sharp Z. (2006), "Principles of Stable Isotope Geochemistry", (Prentice Hall).Template:Full
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