The influence of mixed salts on the capacity of HIC adsorbers: A predictive correlation to the surface tension and the aggregation temperature

Hydrophobic interaction chromatography (HIC) is one of the most frequently used purification methods in downstream processing of biopharmaceuticals. During HIC, salts are the governing additives contributing to binding strength, binding capacity, and protein solubility in the liquid phase. A relatively recent approach to increase the dynamic binding capacity (DBC) of HIC adsorbers is the use of salt mixtures. By mixing chaotropic with kosmotropic salts, the DBC can strongly be influenced. For salt mixtures with a higher proportion of chaotropic than kosmotropic salt, higher DBCs were achieved compared with single salt approaches. By measuring the surface tensions of the protein salt solutions, the cavity theory—proposed by Melander and Horváth—that higher surface tensions lead to higher DBCs, was found to be invalid for salt mixtures. Aggregation temperatures of lysozyme in the salt mixtures, as a degree of hydrophobic forces, were correlated to the DBCs. Measuring the aggregation temperatures has proven to be a fast analytical methodology to estimate the hydrophobic interactions and thus can be used as a measure for an increase or decrease in the DBCs. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:346–354, 2016