Definition of partition coefficient in chromatography
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the physical sciences, a partition-coefficient (P) or distribution-coefficient (D) is the ratio of concentrations of a compoundin a mixture of two immiscible phases at equilibrium. This ratio is therefore a measure of the difference in solubility of the compound in these two phases. The partition-coefficient generally refers to the concentration ratio of un-ionized species of compound whereas the distribution-coefficient refers to the concentration ratio of all species of the compound (ionized plus un-ionized).[1]
In the chemical and pharmaceutical sciences, both phases usually are solvents.[2] Most commonly, one of the solvents is water while the second is hydrophobic such as 1-octanol.[3] Hence the partition coefficient measures how hydrophilic ("water-loving") or hydrophobic ("water-fearing") a chemical substance is. Partition coefficients are useful in estimating the distribution of drugs within the body. Hydrophobic drugs with high octanol/water partition coefficients are mainly distributed to hydrophobic areas such as lipid bilayers of cells. Conversely hydrophilic drugs (low octanol/water partition coefficients) are found primarily in aqueous regions such as blood serum.[4]
If one of the solvents is a gas and the other a liquid, a gas/liquid partition coefficient can be determined. For example, the blood/gas partition coefficient of a general anestheticmeasures how easily the anesthetic passes from gas to blood.[5] Partition coefficients can also be defined when one of the phases is solid, for instance, when one phase is a molten metal and the second is a solid metal,[6] or when both phases are solids.[7]The partitioning of a substance into a solid results in a solid solution.
Partition coefficients can be measured experimentally in various ways (by shake-flask, HPLC, etc.) or estimated via calculation based on a variety of methods (fragment-based, atom-based, etc.).
In the chemical and pharmaceutical sciences, both phases usually are solvents.[2] Most commonly, one of the solvents is water while the second is hydrophobic such as 1-octanol.[3] Hence the partition coefficient measures how hydrophilic ("water-loving") or hydrophobic ("water-fearing") a chemical substance is. Partition coefficients are useful in estimating the distribution of drugs within the body. Hydrophobic drugs with high octanol/water partition coefficients are mainly distributed to hydrophobic areas such as lipid bilayers of cells. Conversely hydrophilic drugs (low octanol/water partition coefficients) are found primarily in aqueous regions such as blood serum.[4]
If one of the solvents is a gas and the other a liquid, a gas/liquid partition coefficient can be determined. For example, the blood/gas partition coefficient of a general anestheticmeasures how easily the anesthetic passes from gas to blood.[5] Partition coefficients can also be defined when one of the phases is solid, for instance, when one phase is a molten metal and the second is a solid metal,[6] or when both phases are solids.[7]The partitioning of a substance into a solid results in a solid solution.
Partition coefficients can be measured experimentally in various ways (by shake-flask, HPLC, etc.) or estimated via calculation based on a variety of methods (fragment-based, atom-based, etc.).
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