Characterization of polymer-based monolithic capillary columns by inverse size-exclusion chromatography and mercury-intrusion porosimetry

Organic-polymer monolithic capillary columns were prepared in fused-silica capillaries by a radical copolymerization reaction of butyl methacrylate and ethylene dimethacrylate monomers in the presence of 1,4-butanediol and 1-propanol as porogen solvents and azobisisobutyronitrile as the initiator. The porous properties could be influenced by changing the ratio of porogen solvents, while keeping the monomer content constant, or by changing the ratio of monomers to porogen in the polymerization mixture. The resulting chromatographic properties, such as porosity, permeability were determined under high-pressure liquid chromatography (HPLC) conditions. The mesopore size distributions of the monolithic materials determined with inverse size-exclusion chromatography (ISEC) were compared with those measured by mercury-intrusion porosimetry. Both techniques are complementary. While mercury-porosimetry measures the entire range of pore sizes and provides more physical information on the monoliths, ISEC is very suitable for determining the size of mesopores in the swollen monoliths.