ABSTRACT
Equilibria between ion exchangers (ion-exchange resins) and
solutions are one of the most important factors in ion-exchange
chromatography. The equilibrium relationship determines the
distribution of solutes (proteins) between gel phase (stationary
phase) and outer solution (mobile phase). It is influenced by
various factors, such as ionic strength of the solution, protein
concentration, pH, and types of ion exchangers. The depend-
ency of the distribution coefficient of protein on ionic strength
and pH is closely related to the elution pattern, that is, peak
position, peak width, and so on (see Chap. 2). Thus, equi-
librium should be expressed in a quantitative fashion as a func-
tion of the system variables in order to predict the elution pro-
file in column operations. However, experimental as well as
theoretical approaches to equilibria with proteins are considerably
hindered in comparison with those for low-molecular-weight in-
organic ions (e.g., Helfferich, 1962), since the ion-exchange
chromatography of proteins is a relatively new technology and
equilibria with macromolecules, such as proteins, are much more
complicated than those with inorganic ions. Special regard
should be paid to the properties of proteins. Although proteins
are biopolymers composed of distinct monomer units, that is,
amino acids linked by peptide bonds, their physical properties
are usually much different from those of the simple assembly of
individual amino acids. In an extreme case, those proteins with
the same net charge and molecular weight but with different
configurations exhibit different behaviors against ion exchangers.
