mass fractionation

Isotopic fractionation is the process where one isotope of an element becomes more concentrated than another during a chemical or physical change. While isotopes of an element have the same chemical properties, their differing masses cause subtle effects. These differences can lead to variations in equilibrium constants for chemical reactions, resulting in slightly different amounts of products formed from reactants with different isotopes.1

The extent of this fractionation is measured by a fractionation factor, alpha (\u03b1), which is the ratio of isotope concentrations in one compound compared to another. For example, during the precipitation of calcium carbonate, oxygen-18 is enriched by 2.5 percent compared to oxygen-16. This temperature-dependent fractionation can be used to determine past water temperatures. Similarly, during photosynthesis, carbon-12 is preferentially incorporated over carbon-13, enriching the resulting organic matter. Physical processes like evaporation and condensation also cause isotopic fractionation, with lighter isotopes often being enriched in evaporated substances.1