Effects of pH and Ionic Strength on Ultrafiltration of Bovine Serum Albumin by Zirconia Membrane

Abstract

This research elucidated the effects of pH and ionic strength on an ultrafiltration of the bovine serum albumin (BSA) solution through a zirconia membrane (Carbosep M2, Tech-Sep).The result showed that the rejections of BSA at pH 3.0-8.5 were not significantly different (in the range of 81-89%). The lowest permeate flux (F_BSA/ F_DI,) was obtained at pH 5.0, the value near the isoeletric point (iep) of BSA. At this pH, the net charge of BSA approached zero and BSA was least soluble. Therefore, the suitable pH of BSA solution should be far from the iep of BSA but not close to the denaturing pH of BSA. That is, pH 6.5-7.5 should be used. The membrane was found to be able to retain sodium chloride with rejection of 2.16-16.01%. The investigation on the effect of ionic strength revealed that the sodium chloride in BSA solution had no significant effect on rejection. Adding sodium chloride into the BSA solution had a benefit of increasing the solubility of BSA, consequently, reduced the adsorption of protein on membrane.However, the flux was lowered when the sodium chloride was added since the increasing of osmotic pressure difference across the membrane caused by rejected sodium chloride. Therefore,the ionic strength should be as low as possible in order to minimize the rejection of sodium chloride as well as the osmotic pressure difference across the membrane. These lead to the highest permeate flux.

Keywords : BSA Solution/pH/Ionic Strength/Zirconia Membrane/Ultrafiltration