Acid-base extraction

The idea behind this technique is that ionic salts tend to be water-soluble while neutral molecules tend not to be. If a compound has a functional group which can be used to form a salt, this process can be used to separate it from other compounds without such a functional group. In the example below, carboxylic acid is separated from an alkane:

Bases can be separated using the same principles, but with addition of an acid instead of a base.

For example consider a mixture of an amine and an alkane. Protonating the primary amine with HCl gives [R-NH₄]⁺[Cl]^- - which will drift into the aqueous layer while the alkane stays in the organic layer.