Investigation of salt properties with electro-acoustic measurements and their effect on dynamic binding capacity in hydrophobic interaction chromatography

• Published in: Journal of Chromatography A Vol. 1177; no. 2; pp. 215 - 225
• Main Authors: Müller, Egbert, Faude, Alexander
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 11.01.2008; Amsterdam; New York: Elsevier; Elsevier
• Subjects: Acoustics; Ammonium Sulfate - chemistry; Analytical, structural and metabolic biochemistry; Biological and medical sciences; Chromatography, Liquid - instrumentation; Chromatography, Liquid - methods; Citrates - chemistry; Dynamic binding capacity in HIC; Electro-acoustic measurements for salt characterization in HIC; Extended scaling theory in HIC; Fundamental and applied biological sciences. Psychology; General aspects, investigation methods; Hydrogen-Ion Concentration; Hydrophobic and Hydrophilic Interactions; Ion association ion hydration in HIC; Ions - chemistry; Models, Chemical; Molecular Weight; Osmolar Concentration; PH dependency of HIC; Protein Binding; Proteins; Proteins - chemistry; Salts - chemistry; Sodium Chloride - chemistry; Vibration; Water - chemistry; PH dependency of HIC; Ion association ion hydration in HIC; Extended scaling theory in HIC; Dynamic binding capacity in HIC; Electro-acoustic measurements for salt characterization in HIC; Electroacoustics; Hydration; Ion pair; Theoretical study; Mobile phase; Protein; Characterization; Binding capacity; Salt effect; Hydrophobic chromatography; Medium effect; pH
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2007.11.008

The pH dependence in hydrophobic interaction chromatography (HIC) is usually discussed exclusively in terms of protein dependence and there are no clear defined trends. Many of the deviations from an ideal solution are caused solely by the high salt concentration, as protein concentration is usually negligible. So pH dependency in hydrophobic interaction chromatography could also be the result of pH dependent changes of ion properties from the salt solution. The possibility that pH dependent ion hydration or ion association in highly concentrated salt solutions may influence the dynamic protein binding capacity onto HIC resins was investigated. In buffer solutions commonly used in HIC e.g. sodium chloride, ammonium sulphate and sodium citrate pH dependent maxima in the electro-acoustic signals were found. These maxima are related to an increase of the ion sizes by hydration or ion association. At low ionic strength the maxima are in the range between 4.5 and 6 and they increased in concentrated electrolyte solutions to values between 6 and 8. The range of these maxima is in the same region as dynamic protein binding capacity maxima often observed in HIC. For a qualitative interpretation of this phenomenon of increased protein stabilization by volume exclusion effect extended scaling theory can be used. This theory predicts a maximum of protein stabilization if the ratio of salt ion diameter to water is 1.8. According to the hypothesis raised here, if the pH dependent ratio of salt ion diameter to water approaches this value the transport of the protein in the pore system is less restricted and an increase in binding capacity can be produced.