Separations Based on a Partitioning Between Phases

The most important class of separation techniques is based on the selective partitioning of the analyte or interferent between two immiscible phases. When a phase containing a solute, S, is brought into contact with a second phase, the solute partitions itself between the two phases. 

An equilibrium constant describing the distribution of a solute between two phases only one form of the solute is used in defining the partition coefficient 

The process by which a solute is transferred from one phase to a new phase. 

Schematic of a liquid-liquid microextraction showing syringe needle with attached 1-pL droplet. 

Extraction Between Two Phases When the sample is initially present in one of the phases, the separation is known as an extraction. In a simple extraction the sample is extracted one or more times with portions of the second phase. Simple extractions are particularly useful for separations in which only one component has a favorable distribution ratio. Several important separation techniques are based on simple extractions, including liquid-liquid, liquid-solid, solid-liquid, and gas-solid extractions. 

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