Role of pH and Ionic strength on weak cation exchange macroporous Hydrogel membranes and IgG capture

• Characterization of weak cation exchange macroporous hydrogel membrane.
• pH and ionic strength affected membrane charge, swelling and pore size profiles.
• Correlations for IgG binding/elution, pH and membrane characteristics were developed.

The surface charge of weak cation exchange membranes, consisting of functionalized macroporous hydrogel coated nonwoven support material, was related to its global swelling. Pore size visualization and analysis by Field Emission Scanning Electron Microscopy (FESEM) of hydrated membranes subjected to freeze drying preserved the hydrogel macroporous structure and showed pores generally an order of magnitude larger than immunoglobulin G (IgG). At pH 6 and higher, the membrane average pore size was high reflecting the strong negative charge of the carboxylic acid groups. At pH below 5.5, the membrane average pore size was lower reflecting the nearly zero surface charge of the membrane material. The charge of IgG was the predominant factor responsible for IgG binding and elution. Maximum IgG binding capacity was observed at pH 4.8 and 0 M KCl, whereas highest IgG elution was obtained at pH 7 and 0 M KCl. The presence of KCl at pH 4.8 decreased IgG binding capacity while KCl addition at pH 7 did not affect IgG recovery but KCl addition was required for IgG elution at pH 4.5. Convective transport limitations, which were investigated in a dynamic flow through system, were reduced while strong asymmetry of the breakthrough curve remained when the feed flow rate was increased. Protein accumulation at the membrane surface and in the membrane pores may exist during dynamic operation. Further work should be devoted to the investigation of protein accumulation and its distinction from protein binding.

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