Solvent Extraction:

In the world of chemicals a substance is rarely found in a pure form. Also whatever may  be the method  of preparation,  a chemical  entity,  in the truest  sense,  is never obtained  free  of  impurities.  With the rapid growth of chemical technology, the chemists are called upon to devise methods to obtain substances in a pure form. There is another problem that if we look into the magic box of analytical techniques there is hardly a technique which is truly specific for the quantification of a constituent. Both these scenarios necessitate the development of effective methods of separations. The analytical   chemists   have   never   lagged   behind   in developing   new methods   of separations and bring ingenuity in the existing ones.

The general criteria for the selection of a separation technique have been discussed. In a broader sense, the technique to be adopted for affecting the separations depends upon the nature of the host matrix and the associated impurities. Needless to say, the amount to be handled is also important. But whatever may be the situation you always look for a technique which may be convenient, fast and economical. It should be one, which, if the need be, can be conveniently scaled up from the bench level to the plant scale. Liquid-liquid extraction, popularly known as solvent extraction, comes close to satisfying the above criteria. Besides this, it is a very versatile technique. It is as effective for organic as for inorganic compounds. Moreover, such a broad spectrum of extraction systems is available that any given set of impurities can be dealt with. One definite advantage that the extraction methods offer over the widely used precipitation technique is that much cleaner separation can be achieved by the former. In the precipitation methods, contamination by coprecipitation is a big limitation which is minimized with difficulty, whereas analog of coprecipitation i.e., coextraction (extraction of impurities which should not extract) is almost unknown in solvent extraction. Moreover, precipitation methods fail at micro concentrations because there has to be a sufficient amount of the substance to get precipitated.