ABSTRACT
This chapter addresses three types of chromatographic modes used in protein separations with kosmotropic additives: conventional reversed-phase liquid chromatography, hydrophobic interaction chromatography and ion-pairing chromatography. Kosmotropic chromatography, originally referred to as “salting out chromatography,” is based on a decreased solubility of an analyte in the mobile phase caused by the presence of salts of specific types. The effect of kosmotropic salts on the salting out of proteins from the mobile phase in reversed-phase liquid chromatography follows the Hofmeister series. A classification between chaotropic and kosmotropic ions arose initially according to an erroneous belief that anions have no hydration layer. Kosmotropic ions are supposed to induce local water structuring through hydration. The addition of kosmotropic salts has a small effect of increasing resolution, while also improving peak shape and selectivity. The use of mobile phases containing kosmotropic salts, such as ammonium sulfate, has been suggested.
