Liquid-Liquid extraction is a versatile and dependable separation technique wherein an aqueous solution is usually brought into contact with another organic solvent, exclusively immiscible with the former, so as to affect a legitimate and actual transfer of either one or more solutes into the latter. The normal-feasible separations which can thus be achieved are found to be rather easy, fast, convenient and effective resonably. Invariably such separations may be performed by shaking the two liquids in a separatory funnel for a few minutes ; and may be extended either to large quantities of pharmaceutical substances or trace levels.
In the case of pharmaceutical chemicals that are mostly ‘organic solutes’, the liquid-liquid extraction system may very often make use of two immiscible organic solvents (e.g., alcohol and ether) instead of the aqueous-organic type of extraction. On the contrary, the ‘inorganic solutes’ normally encountered are in-variably in aqueous solutions ; therefore, it has become absolutely necessary to produce such neutral sub-stances out of them, for instance ion-association complexes and metal-chelates (using organic-ligands) that may be extracted into an appropriate organic solvent.
In short, liquid-liquid extraction has been employed predominantly and effectively not only for the pre-concentration and isolation of a ‘single’ chemical entity just before its actual estimation, but also for the extraction of classes of organic compounds or groups of metals, just prior to their usual estimation either by chromatographic techniques or by atomic-absorption methods.