Monovalent ion-mediated fouling propensity of model proteins during low-pressure membrane filtration

Abstract

In this study, we explored the response of membrane filtration behavior of bovine serum albumin (BSA) to various monovalent salts (i.e., NaCl, KCl, CsCl, NaBr, NaI) at 15 mM and 150 mM ionic strengths. The results demonstrated that the charge of BSA tended to be less negative with an increase in ionic strength. The presence of monovalent ions also resulted in the increased size of BSA. However, little change was observed in the viscosity of BSA with the involvement of monovalent ions (with the exception of 150 mM CsCl). The changes in the characteristics of BSA were primarily caused by their interaction with cations, and the greater specific interaction between Cs+ and BSA led to a significant increase in the size and viscosity of BSA. In spite of the substantial dependence of the characteristics of BSA (i.e., size, zeta potential) on cations, the fouling behaviors of BSA were primarily determined by anion identity. Specifically, the order of the ability of anion identity to reduce the flux decline rate seemed to be I- > Br- ∼ or > Cl-, which seemed to be ascribed to the changes in electrostatic repulsion between BSA and the membranes caused by anions. © 2015 Elsevier B.V. All rights reserved.