Distribution ratios:
D1 and D2 are the distribution ratios of components 1 and 2, respectively. For a good separation, β should deviate from unity as largely as possible. The ingenuity and knowledge of a separation chemist is tested to find conditions where β should deviate from unity. With the available data and knowledge of chemistry, in most of the cases, it is not a problem. An elaboration of this will be taken up later in Unit 3, Sec. 3.4 where a detailed discussion on the different approaches adopted for metal ion separation are included. Although most of the separations involving solvent extraction are based on favourable separation factors, it is occasionally necessary to resort to separations where the distribution ratios of the components of the mixture may not be much different. In such situations, it is necessary to employ fractionation methods in which distribution, transfer and recombination of different fraction is advised to be performed a number of times to achieve a certain level of separation.