Partition coefficient
A partition coefficient indicates how a substance is distributed between two immiscible phases .
Classification
Liquid-liquid
In the case of immiscible substances, two, rarely several, liquid phases can occur in a liquid , which form a miscibility gap (liquid-liquid equilibrium). A third substance, which is added in small quantities, usually dissolves to a different extent in both phases.
With
- K: partition coefficient (often also referred to as P, P stands for Partition Coefficient )
- c L1 : concentration of the third substance in the first liquid phase (alternatively: in the upper phase)
- c L2 : concentration of the third substance in the second liquid phase (alternatively: in the lower phase)
The best-known liquid-liquid partition coefficient is the octanol-water partition coefficient (K OW ), which describes the distribution of a component between a water-rich phase and a low-octanol phase and an octanol-rich and low-water phase. This distribution is used in the liquid-liquid extraction .
Gas-liquid
The distribution between a gas and a liquid is described by Henry's Law .
Solid-liquid
This class includes soil-water or sediment-water partition coefficients (K SW , SW stands for Soil-Water). This coefficient determines which quantities of a substance are adsorbed on soil or sediment particles or are absorbed by them .
determination
The distribution coefficients can be determined by measuring the concentrations in the individual phases or can be calculated approximately using quantitative structure-activity relationships ( QSAR ).
meaning
Distribution coefficients are important wherever phase equilibria play a role in heterogeneous systems , e.g. B. technical extraction processes or when determining the distribution of chemical substances in biological systems in the context of pharmacokinetics .
literature
Edward J. Baum, "Chemical Property Estimation. Theory and Application. ", Lewis Publishers, 1998 ( ISBN 0-87371-938-7 )