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, biochemistry,{{cite journal |last1=Akoka |first1=Serge |last2=Remaud |first2=Gérald |title=NMR-Based Isotopic and Isotopomic Analysis |journal=Progress in Nuclear Magnetic Resonance Spectroscopy |date=October–December 2020 |volume=120-121 |pages=1–24 |doi=10.1016/j.pnmrs.2020.07.001 |pmid=33198965 |bibcode=2020PNMRS.120....1A |url=https://www.sciencedirect.com/science/article/abs/pii/S0079656520300224 |access-date=2024-02-11}} food science,{{cite journal | author = Ogrinc, N; Kosir, IJ; Spangenberg, JE & Kidric, J | date = June 2003 | title = The Application of NMR and MS Methods for Detection of Adulteration of Wine, Fruit Juices, and Olive Oil. A Review. | journal = Anal. Bioanal. Chem. | volume = 376 | issue = 4 | pages = 424–430 | doi = 10.1007/s00216-003-1804-6 | pmid = 12819845}} 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, nuclear magnetic resonance methods (specialised techniques,) cavity ring-down spectroscopy,{{citation needed lead|date=March 2025}} etc., to measure ratios of isotopes, important tools to understand geochemical and biological systems, past and present.{{citation needed lead|date=March 2025}} For example, biochemical processes cause changes in ratios of stable carbon isotopes incorporated into biomass.{{citation needed lead|date=March 2025}}

Definition

Stable isotopes partitioning between two substances A and B can be expressed by the use of the isotopic fractionation factor (alpha):

:{{math|α_A-B {{=}} R_A/R_B}}

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.{{Cite web | author= Kendall, Carol |author-link=Carol Kendall (scientist) | year=2004 | title= Fundamentals of Stable Isotope Geochemistry | series = Isotope Tracers Project | location = Menlo Park, CA | publisher = USGS | url= http://wwwrcamnl.wr.usgs.gov/isoig/res/funda.html | access-date= April 10, 2014}}{{cite book | chapter-url=https://www.degruyter.com/document/doi/10.1515/9783110589771-003 | doi=10.1515/9783110589771-003 | chapter=Preface to Volume 21 | title=Metals, Microbes, and Minerals - the Biogeochemical Side of Life | date=2021 | pages=ix-xii | isbn=978-3-11-058977-1 }}

Types

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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), and transient kinetic isotope fractionation.{{cn|date=March 2025}}

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".

Isotope fractionation

Definition

Types

Example

See also

References

Further reading