Encyclopedia of Lipidomics

Living Edition
| Editors: Markus R. Wenk

Liquid Extraction: Partition Coefficient

Living reference work entry
DOI: https://doi.org/10.1007/978-94-007-7864-1_91-1

Keywords

Partition Coefficient Solvent System Extraction Efficiency Lipid Extraction Polar Solvent
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
The “partition coefficient, (K)” defines the solubility differences for a given compound between two immiscible solvents at equilibrium. It is also calculated as the ratio of the concentration of the compound in a mixture of two immiscible solvent systems, “solvent x” and “solvent y.” If the solute A is initially soluble in one single solvent (solvent y), then eventually dissolves in both immiscible solvents and partitions to the second solvent (solvent x), then the distribution of the solute reaches equilibrium, and then partition coefficient, K, of solute A is given by
$${\mathbf{K}}_{\left(\mathbf{solvent}\ \mathbf{x}/\mathbf{solvent}\ \mathbf{y}\right)} = \left[{\mathbf{A}}_{\mathbf{solvent}\ \mathbf{x}}\right]/\left[{\mathbf{A}}_{\mathbf{solvent}\ \mathbf{y}}\right]$$

Where, [Asolvent x] is the concentration of solute A in the solvent x, extract, and [Asolvent y] is the concentration of solute A in the solvent y, raffinate.

Partition coefficient of a compound in between two immiscible solvents depends on many factors, such as temperature, pH, viscosity, and polarity of solvents. When the volumes of solvent y and solvent x are identical and assumed to be unchanged by the extraction, the concentration of solute A in the raffinate is given by the difference between the extracted and unextracted concentrations of solute A in solvent y. Due to the ionized form of solute A, either acidic or basic, solute A is more hydrophilic than its neutral form. When the solute A is acidic, a lower partition coefficient is expected at high pH and if the solute A is basic, a lower partition coefficient is expected at low pH. However, if the solute A is not ionized in solvent y, the partition coefficient remains unchanged.

Lipids are made of long chains of hydrocarbons and tend to be nonpolar. This means that they have poor solubility in polar solvents such as water but are highly soluble in the nonpolar or weak polar organic solvents, including methanol, chloroform, benzene, and acetone. The solubility of lipids in nonpolar organic solvents provides a guide for the selection of a suitable extraction solvent for liquid extraction. Lipid extraction using either monophasic or biphasic liquid-liquid extraction improves the detection of lipid analysis. In a liquid-liquid extraction system with three components, i.e., two solvent systems and the solute that are in equilibrium, a phase diagram can be used to select the optimum solvent systems with the ratios of each solvent in the extraction process efficiently.

When considering extraction of lipids using a liquid-liquid solvent system, the partition coefficient plays an important role as discussed. Choosing the optimum solvent system along with additional factors contributing to increase the partition coefficient will improve the extraction efficiency of lipids.