The partition coefficient is a ratio of concentrations of un-ionized compound between the two solutions. To measure the partition coefficient of ionizable solutes, the pH of the aqueous phase is adjusted such that the predominant form of the compound is un-ionized. The logarithm of the ratio of the concentrations of the un-ionized solute in the solvents is called log P: The log P value is also known as a measure of lipophilicity.
Read more about Partition Coefficient: Distribution Coefficient and Log D, Prediction, Some Octanol-Water Partition Coefficient Data, Limitations