The key difference between partition coefficient and distribution coefficient is that the partition coefficient refers to the concentration of un-ionized chemical species of a compound whereas the distribution coefficient refers to the concentration of both ionized and un-ionized chemical species of a compound.
The two terms partition coefficient and distribution coefficient are usually used interchangeably because both these terms nearly express the same idea about the distribution of a chemical species between two mediums. However, these terms differ from each other depending on the chemical species we are considering in the calculation.
CONTENTS
1. Overview and Key Difference
2. What is Partition Coefficient
3. What is Distribution Coefficient
4. Side by Side Comparison – Partition Coefficient vs Distribution Coefficient in Tabular Form
5. Summary
What is Partition Coefficient?
The partition coefficient is the ratio of concentrations of un-ionized species of a compound in a mixture of two immiscible phases. We usually denote this phenomenon as “P”. The two different phases should be in equilibrium with each other to determine the partition coefficient of that two-phase system. This ratio represents the measure of the solubility of each un-ionized species in this mixture.
Figure 01: Determination of Partition Coefficient in a Diagram
Generally, the two immiscible phases we consider here are solvents. Mostly, it is a water-organic solvent system. Therefore, we often consider hydrophilic–hydrophobic systems when determining the partition coefficient. There, the partition coefficient is a measure of the lipophilicity or the hydrophobicity of the solute that we are interested at. This phenomenon is very important in determining drug distribution throughout our body.
What is Distribution Coefficient?
Distribution coefficient is the ratio of the concentration of both ionized and un-ionized species of a compound in a mixture of two immiscible phases. We can denote this phenomenon as “D”. Here, one of the two immiscible phases is essentially water or an aqueous solution. The other phase is usually a hydrophobic phase which is immiscible with water (or any other aqueous phase we use here). Usually, we give this value as a logarithmic value because it is a very small value.
What is the Difference Between Partition Coefficient and Distribution Coefficient?
Although we use the terms partition coefficient and distribution coefficient interchangeably, they are different from each other. The key difference between partition coefficient and distribution coefficient is that the term partition coefficient refers to the concentration of un-ionized chemical species of a compound whereas the term distribution coefficient refers to the concentration of both ionized and un-ionized chemical species of a compound.
When considering the two immiscible phases, in determining partition coefficient, we mostly use a combination of water and a hydrophobic phase while in determining the distribution coefficient we essentially use an aqueous phase with another suitable phase.
The following table summarizes the difference between partition coefficient and distribution coefficient.
Summary – Partition Coefficient vs Distribution Coefficient
Although we use the terms partition coefficient and distribution coefficient interchangeably, they are different from each other. These terms differ from each other depending on the chemical species we consider for each calculation. The key difference between partition coefficient and distribution coefficient is that the term partition coefficient refers to the concentration of un-ionized chemical species of a compound whereas the term distribution coefficient refers to the concentration of both ionized and un-ionized chemical species of a compound.
Reference:
1.“Partition Coefficient.” Wikipedia, Wikimedia Foundation, 23 Sept. 2019, Available here.
2. “Partition Coefficient.” ScienceDirect Topics, Available here.
3. Oscarson, Dennis W., and Harold B. Hume. “Effect of the Solid: Liquid Ratio on the Sorption of
Sr2 and Cs on Bentonite.” Adsorption of Metals by Geomedia, 1998, pp. 277–289.,
doi:10.1016/b978-012384245-9/50013-x.
Image Courtesy:
1. “Partitioning coefficient (Kd)” By Perdula – Own work (CC BY-SA 3.0) via Commons Wikimedia