Limitations
The procedure works only for acids and bases with a large difference in solubility between their charged and their uncharged form. The procedure does not work for:
- Zwitterions with acidic and basic functional groups in the same molecule, e.g. glycine which tend to be water soluble at most pH.
- Very lipophilic amines that do not easily dissolve in the aqueous phase in their charged form, e.g. triphenylamine and trihexylamine.
- Very lipophilic acids that do not easily dissolve in the aqueous phase in their charged form, e.g. fatty acids.
- Lower amines like ammonia, methylamine, or triethanolamine which are miscible or significantly soluble in water at most pH.
- Hydrophilic acids like acetic acid, citric acid, and most inorganic acids like sulfuric acid or phosphoric acid.
Read more about this topic: Acid-base Extraction
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