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Medical Definition of Anion exchange
1. The process by which an anion in a mobile (liquid) phase exchanges with another anion previously bound to a solid, positively charged phase, the latter being an anion exchanger. It takes place when Cl- is exchanged for OH- in desalting. The reaction is Cl- (in solution) + (OH- on anion exchanger+) → (Cl- on anion exchanger) + OH- (in solution); combined with cation exchange, NaCl is removed from solution. Anion exchange may also be used chromatographically, to separate anions, and medicinally, to remove an anion (e.g., Cl-) from gastric contents or bile acids in the intestine. (05 Mar 2000)