Excluded Cosolvent in Chromatography

The concept of cosolvent exclusion was developed by a group of Timasheff's laboratory in 1970-1990 and is currently used widely to explain the effects of a variety of cosolvents on the stability and solubility of macromolecules. Not surprisingly, these concepts have had substantial influence in the fields of formulation, protein folding and unfolding, but they have perhaps more surprisingly found their way into the field of chromatography. A variety of excluded cosolvents have been used to enhance binding and resolution of proteins and other macromolecules in ion exchange, hydroxyapatite, affinity, and hydrophobic interaction chromatography. These cosolvents include salting-out salts, amino acids and polymers, and frequently polyethylene glycol (PEG). A new mode of chromatography, termed "steric exclusion chromatography," was recently introduced. It employs hydroxylated solid phase surfaces. Steric exclusion of the PEG stabilizes the association of macromolecules with the solid phase. Elution is achieved by reducing the PEG concentration. Magnetic particles are also used in this chromatography. This review summarizes the concepts of preferential cosolvent exclusion and its applications in column chromatography.