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Partition equilibrium is a special case of chemical equilibrium. The most common chemical equilibrium systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such as two liquids that do not mix (are immiscible).[1] Partition equilibria are described by Nernst's distribution law.

Example

For example, ammonia (NH3) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl3) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established:

Kc = [NH3 (CHCl3)]/[NH3 (aq)]        (where Kc is the equilibrium constant)

The equilibrium concentrations of ammonia in each layer can be established by titration with standard acid solution. It can thus be determined that Kc remains constant, with a value of 0.4 in this case.

Partition coefficient

Main article: Partition coefficient

This particular kind of equilibrium constant measures how a substance distributes or partitions itself between two immiscible solvents.[2] It is called the partition coefficient or distribution coefficient.

Partition equilibrium chromatography

Partition equilibrium chromatography is a type of chromatography that is typically used in gas chromatography (GC) and high performance liquid chromatography (HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas.

See also

References

  1. ^ Rudrapal, Mithun; Kothawade, Aniket P.; Ezzat, Shahira M.; Egbuna, Chukwuebuka (2022), "Bioanalysis: methods, techniques, and applications", Analytical Techniques in Biosciences, Elsevier, pp. 1–24, doi:10.1016/b978-0-12-822654-4.00002-6, ISBN 978-0-12-822654-4, retrieved 2024-02-01
  2. ^ Kwon Y (2001). "4.2.4: Partition and Distribution Coefficients". Handbook of Essential Pharmacokinetics, Pharmacodynamics and Drug Metabolism for Industrial Scientists. New York: Kluwer Academic/Plenum Publishers. p. 44. ISBN 978-1-4757-8693-4.
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