Electrostatic effects on protein partitioning in size-exclusion chromatography and membrane ultrafiltration

Although size-exclusion chromatography and membrane ultrafiltration are generally viewed as size-based separation processes, there is considerable evidence for the importance of electrostatic interactions. Experimental studies of size-exclusion chromatography and membrane ultrafiltration were performed in parallel using both neutral dextrans and charged proteins. Data for protein retention time and membrane sieving clearly indicate that the effective protein size increases with decreasing ionic strength due to the reduction in electrostatic shielding. These results were quantified using available theoretical models for the partitioning of charged solutes. The data clearly demonstrate the similarity of the electrostatic interactions and partitioning effects in size-exclusion chromatography and membrane ultrafiltration.