Chapter 7 Ion-exchange chromatography

Abstract

Publisher Summary This chapter focuses on ion-exchange chromatography. Ion exchange is the reversible interchange of ions of like sign between a solution and a solid, insoluble body. The solid must carry ions of its own, fixed ions that are attached by covalent bonds to the molecular framework, and exchangeable or mobile ions, held by electrostatic forces, that can move in and out of the solid and change places with ions from the solution, conserving electro-neutrality. Most of the mobile ions have charges opposite to the charges of the fixed ions and are called counterions. However, ions having the same charge sign as the fixed ions may also be present. They are called co-ions, and their concentration in the exchanger is regulated by the Donnan equilibrium that is discussed in the chapter. The solid exchanger must have an open molecular framework that allows the mobile ions to move freely in and out. Some solid exchangers have an extensive surface that carries fixed ions and an electrical double layer; clay minerals are of this type. Conventional ion exchangers have a three-dimensional structure that is porous on the molecular scale.