Buffers for solvent extraction

Many natural products, pharmaceuticals and synthetic organic chemicals are weak acids or bases which, in their non-ionized forms can be extracted from aqueous solutions by suitable organic solvents whereas, if the pH is such that they are ionized, their retention in the aqueous phase is favoured. By using buffers to control the pH of the solution, and hence to govern the concentration ratio of ionized and neutral forms, it is frequently possible to improve the selectivity of such separation processes. The use of buffers for this purpose was very important in the separation of individual penicillins and in preparing synthetic antimalarials. 

Extraction of metal ions as complexes with organic 

In all cases, the buffer components should be readily soluble in the aqueous phase but be essentially insoluble in the organic phase. Nor should they form insoluble or complex species with the compounds that are to be extracted. This suggests that highly polar buffers such as citrate and phosphate would ordinarily be the buffers of choice. Acetate buffers are likely to be less suitable because of the possibility of extracting acetic acid into the organic phase. With amine buffers there is the possibility that both the neutral amine and its ion-pair with chloride ion will be extractable. 

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