Preparation of inorganic–organic anion-exchange membranes and their application in plasmid DNA and RNA separation

Inorganic–organic anion-exchange membranes were prepared in this study by coating a precursor, the product of N-[3-(trimethoxysilyl)propyl] ethylene diamine reacted with 3-(triethoxysilyl)propyl isocyanate, on macroporous glass fiber and alumina membranes, followed by bromoethane treatment. The FTIR results demonstrated the successful membrane modification, and the resulted anion-exchange capacities were 6.2 and 1.5 μequiv./cm2, respectively, for modified glass fiber membrane and modified alumina membrane. In batch adsorption process, the corresponding adsorption capacity for plasmid DNA could be sorted by: commercial polymeric SB6407 > modified glass fiber > modified alumina membrane; while for RNA adsorption, the order became: modified glass fiber ≈ SB6407 > modified alumina membrane. The optimal elution condition found from batch desorption performance was: 2 M NaCl in 50 mM Tris–HCl, pH 8 for RNA elution, followed by 1 M NaCl and 20% ethanol in 50 mM Tris–HCl, pH 8 for plasmid DNA elution. In membrane chromatography process, plasmid DNA and RNA could be clearly separated from the feed of 10 μg plasmid DNA + 10 μg RNA mixture or cell lysate by one piece of 47 mm modified glass fiber or SB6407 membrane, but not by the stacked 13 mm modified alumina membranes. The overall plasmid DNA recovery for the modified glass fiber membrane was 98–106%, higher than that of SB6407 membrane (91–96%).