Extractie: effect van pH

Consider a weak base,  B, with a partition coefficient, K, between the organic and aqueous phases.  

While organic bases are usually more soluble in the organic phase, changing the pH can convert them to their water-soluble salt form.

Here, the conjugate acid, BH⁺, has the acid dissociation constant K_a. 

If BH⁺ is soluble only in the aqueous phase, then the distribution coefficient, D,  can be calculated from the total concentration of B.

Substituting for K and K_a and rearranging gives the fraction of neutral base in the aqueous phase.

The pH-dependent distribution ratio implies that a base can be extracted into the aqueous phase as its conjugate acid within a suitable pH range.