Mass transfer characteristics of plasmids in monoliths

The hydrodynamic properties and pore-structure of monoliths based on functionalized poly(glycidyl methacrylate-ethylene dimethacrylate) were characterised by pulse response experiments using different probes representing a wide range of molecular mass. On a small scale, band spreading was found to be caused to the extent of more than 90% by extra-column effects. These monoliths have large channel diameters, providing a suitable chromatography adsorbent for processing of large molecules. Dynamic and static binding capacity for plasmid DNA was investigated. For our model plasmid, consisting of 4.9 kbp, a capacity of 7 mg/mL was observed in comparison to 0.3 mg/mL for a conventional medium designed for protein separation. When plasmids were loaded on the monolith a gradual increase in pressure drop was observed. The channels filled up and the cross-sectional area available for liquid flow decreased. Therefore, a higher pressure drop was observed during elution. This is caused by (i) shrinking of the channels as effect of the high salt concentration, (ii) high viscosity of the mobile phase due to high concentration of plasmids, and (iii) an increase of the hydrodynamic radius of the plasmid with salt concentration from 45 nm at 150 mM to 70 nm at 2 M NaCl, as measured by dynamic light scattering. These types of monoliths are considered to be the preferred adsorbents for plasmid separation.