Britannica Sources used in this answer

How does solvent extraction separate dissolved chemicals between two liquids?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Viking 1 on Mars — sample preparation Viking 1's sample scoop, poised to extract material from the surface of Mars.

Solvent extraction separates dissolved chemicals by leveraging their differing solubilities in two immiscible liquids. When a sample is introduced to these two liquids, the solutes distribute themselves between the phases until they reach an equilibrium state.123

The ratio of the concentrations of a solute in the two solvents is known as the distribution coefficient, which is characteristic of the specific compound and the solvent pair used. Because different substances have unique affinities for each solvent, they distribute unevenly, allowing for partial separation when the two liquid layers are physically separated.213

To achieve higher purity or complete separation, the process can be repeated through multiple equilibrations, often using a countercurrent approach. In this method, fresh solvent is used in successive stages to maximize the removal of the desired component from the original phase. This principle of repeated equilibration is fundamental to the efficiency of the process and is closely related to the mechanisms used in chromatography.412