 | This articleis missing information aboutother fields where isotopic fractionation is observed, e.g., metabolism of natural products, and all methods of analysis thereof, including MS and NMR, all being given balanced treatment. Please expand the article to include this information. Further details may exist on thetalk page.(March 2025) |
Isotope fractionation describesfractionation processes that affect the relative abundance of isotopes, a phenomena that occurs (and so advantage is taken of it) in the studygeochemistry,[1] biochemistry,[2] food science,[3] and other fields. Normally, the focus is onstable isotopes of the same element. Isotopic fractionation can be measured byisotope analysis, usingisotope-ratio mass spectrometry,[1]nuclear magnetic resonance methods (specialised techniques,[2][3])cavity ring-down spectroscopy,[not verified in body] etc., to measureratios of isotopes, important tools to understand geochemical and biological systems, past and present.[not verified in body] For example,biochemical processes cause changes in ratios of stablecarbon isotopes incorporated into biomass.[not verified in body]
Stable isotopes partitioning between two substancesA andB can be expressed by the use of the isotopic fractionation factor (alpha):
whereR is the ratio of the heavy to light isotope (e.g.,2H/1H or18O/16O). Values for alpha tend to be very close to 1.[1][4]
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There are four types of isotope fractionation (of which the first two are normally most important):equilibrium fractionation,kinetic fractionation,mass-independent fractionation (or non-mass-dependent fractionation), andtransient kinetic isotope fractionation.[citation needed]
Isotope fractionation occurs during aphase transition, when the ratio of light to heavy isotopes in the involved molecules changes. As Carol Kendall of theUSGS states in an information page for the USGS Isotope Tracers Project, "water vapor condenses (anequilibrium process), the heavier water isotopes (18O and2H) become enriched in the liquid phase while the lighter isotopes (16O and1H) tend toward the vapor phase".[1]
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