Towards stationary phases for chromatography on a microchip: Molded porous polymer monoliths prepared in capillaries by photoinitiatedin situ polymerization as separation media for electrochromatography

Abstract

Photoinitiated free radical polymerization has been used for the preparation of porous polymer monoliths within UV transparent fused silica capillaries and quartz tubes. These formats were used as models for the preparation of the separation media within channels of microfabricated devices. A mixture of ethylene dimethacrylate, butyl methacrylate, and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid was polymerized in the presence of a porogenic solvent consisting of 1‐propanol, 1,4‐butanediol, and water at room temperature under UV irradiation. Modification of the porogen composition enables the tailoring of pore size within the broad range from ca. 100 to 4000 nm. Scanning electron micrographs confirmed the homogeneity of the porous structure of the materials prepared, even in a quartz tube with a diameter as large as 4 mm. Separation properties of the resulting capillary columns were tested in capillary electrochromatography (CEC) mode using a mixture of thiourea and eight aromatic compounds. Plate number as high as 210 000 plates/m were found for a capillary column with optimized porous properties. The monolithic columns were also able to separate mixtures of peptides.

New advances in microchip fabrication for electrochromatography

“…To overcome the difficulties of stationary phase packing and anchoring problems, rigid macroporous polymer monoliths were introduced in the early 1990s [96]. Different kinds of chemistries were developed to form monolithic rods: polymethacrylate [97], polyacrylamide [98], photo-initiated free radical polymerization of polymethacrylate-based stationary phase [99], polystyrene-based stationary phase for RP chromatogra- phy [100], and molecularly imprinted polymers [101]. Monolithic stationary phases, particle-packed columns, preparation technologies along with their most important applications are summarized and compared in [102].…”

Methacrylate-ester-based Reversed Phase Monolithic Columns for High Speed Separation Prepared by Low Temperature UV Photo-polymerization

“…This advantage is essential to prepare polymer-based monolith in micro fluidic devices. 38,39 In addition, the radical generation rate in the photo-polymerization is able to be controlled independently of the polymerization temperature by varying the light source intensity. In other words, the polymerization temperature can also be changed without considering the radical generation rate.…”

Monolithic stationary phases for fast ion chromatography and capillary electrochromatography of inorganic ions

“…Furthermore, these porous polymer monoliths are ideal for preparation in microfluidic channels and can be confined to specific locations in the channel or a capillary by using UV-initiated polymerisation with a suitable photomask [55]. A further significant advantage of polymer monoliths is their resistance to high pH and temperature [25], so that they are more readily applicable for use as IC columns used in commercial IC instrumentation employing continuously generated hydroxide eluent.…”

“…The deoxygenated polymerisation mixture containing the required ratios of monomers and porogens is introduced into a mould (such as a silica capillary or a polymeric HPLC column body) and exposed either to heat [59], UV light [55] or c-radiation [60] to initiate and maintain the radical polymerisation process over a certain period of time.…”