The method was discovered by Craig and Post. It is consists of 300-400 such chambers. The organic solvent and the aqueous solution is introduced to tube A and then it passes to B. It is shaken and is allowed to attain the equilibrium. Now, the apparatus is tilted so that the upper layer gets decanted through C and is collected in D. When the apparatus is again made vertical. The liquid passes through D into E in the next chamber of A and then to B. The process is repeated till the two liquids gets almost separated.
Application:
1. With the help of this method we can have accurate quantitative analysis of a single as well as the mixture of the components.
2. In this case apparatus required are very simple (separating funnel burette pipets conical flask etc.)
3. Time required for analysis is very small.
4. The method is very well used for detection of traces quantity of substance where precipitation method (Gravimetry) is not possible.
5. Fe+3 ferric ion can be easily extracted by ether from 6 molar HCl solution of the ferrous ally and iron ore.
6. The extraction can also be use in the extraction of metal as metal chelate where later has high solubility in an immiscible solvent such as chloroform and benzene.
7. In industrial and commercial field extraction by counter current extraction is frequently applied in the separation of components where the difference in the distribution coefficient are small.
8. The phenomenon is widely applied in drug analysis.
9. The solvent extraction is used in clinical laboratory.
10. Metal chelates are more soluble in non-polar solvents. Thus Ni(II) in its tetra co-ordinate complex with dimethyl glyoxime can be extracted into chloroform. In presence of citrate or tartrate the precipitation of Fe(III) and Cr(III) can be avoided.
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