3.3.2 Acid-Base Extractions

As mentioned in Section 3.3.1, the pH of the system has an effect on $k_{partition}$. Therefore, the analyst can 'move' some compounds between the phases.

• Neutral organic solutes can be extracted from water, aqueous base or aqueous acid using an appropriate organic solvent.
• For organic bases, such as amines,
  • the 'free base' is often more soluble in non-polar organic solvents than in polar organic solvents, water or aqueous base.
  • the quaternary ammonium salts of amines (formed by reaction with acids) are usually more soluble in polar or aqueous media than non-polar organic solvents. However, note that if the aqueous solvent is basic, amine compounds may be in the free base form.
• For organic acids,
  • the 'free acid' may be more soluble in an organic solvent than in water (or aqueous acid).
  • salts formed by the reaction with base are usually more soluble in aqueous media than in organic solvents. If the aqueous medium is acidic, however, the compound may be in the free acid form and hence be partitioned into the organic phase.