New formats of polymeric stationary phases for HPLC separations: molded macroporous disks and rods

A molding process has been used for the preparation of separation media in different shapes such as rods and flat membrane-like disks. The polymerization is carried out using a mixture of monomers, porogenic solvent and free-radical initiator under conditions that afford macroporous materials with through-pores or channels large enough to provide the high flow characteristics required for applications in chromatography. In contrast to classical suspension polymerization, the solubility of monomers in water does not restrict their use. The versatility of the preparation technique is demonstrated in polymerizations involving both hydrophobic and hydrophilic monomers such as styrene, chloromethylstyrene, glycidyl methacrylate, alkyl methacrylates and acrylamide. Techniques have been developed that allow fine control of the porous properties of the polymers. These, in turn, determine the hydrodynamic properties of the separation devices that contain the molded media. Since all the mobile phase must flow through the separation medium, the mass transport within the molded media is accelerated considerably by convection. Therefore, the separations can be performed at much higher flow rates than in packed columns. This is particularly important for separations of large molecules such as proteins for which diffusion is a serious problem that significantly slows down the separation processes. The molded separation media have been used for the separation of biological compounds using gentle chromatographic modes such as hydrophobic interaction, ion-exchange and affinity chromatography during which the biological activity of the separated compounds is completely retained.