Choosing and developing an extraction method

Liquid-liquid extraction (LLE)

Liquid-liquid extraction (LLE) is a technique dedicated to liquid matrices. The principle involves mixing two immiscible liquids, one being the sample matrix (in which the compound to be extracted is located) and the other the extractant phase (from which the compound is to be extracted).

Both liquids are put into a separating funnel (see diagram), which is vigorously and manually stirred to help with the extraction. Then the separating funnel is left to decant, allowing the two liquids to separate into two phases. The extractant phase is then recovered.

The extraction efficiency is limited: it depends on the partition coefficient (Kp) of the compound to be extracted between each phase.

Diagram of the separating funnel. It contains water at the top, and organic at the bottom. Kp = [Corganic]equilibrium / [Ceau]equilibrium

Several successive extractions are necessary to reach high extraction yields, resulting in large volumes of solvents.

This technique can be used for the extraction (by organic solvent) of a liquid sample or to purify (by aqueous phase) an organic extract. The relative position of each liquid in the separating funnel depends on the respective densities of the two immiscible phases present.