Standard and capillary chromatography, including electrochromatography, on continuous polymer beds (monoliths), based on water-soluble monomers

Continuous polymer beds (acrylic-based beds) have the following advantages over beds packed with beads: (1) For most chromatographic modes they can be synthesized in one step by sucking a solution of appropriate monomers into a chromatographic tube and polymerizing it under such conditions that a polymer rod forms containing channels which permit hydrodynamic flow of the mobile phase at a relatively low back pressure. The expensive and time-consuming preparation of beads by the conventional suspension-polymerization procedure is thus omitted, as well as the packing step. (2) The monomers are water-soluble, which means that the polymer bed is biocompatible and that no organic solvents are required for the synthesis, which is attractive from an environmental and economical point of view (the destruction or regeneration of organic solvents often costs more than the purchase). (3) The bed can be prepared in situ as described above or, alternatively, by simple packing with bed material synthesized separately by the same procedure. The latter alternative permits a great number of columns to be packed from the same batch. (4) The rate of success of the preparation of beds is close to 100%. (5) The gel particles constituting the bed are nonporous to increase the mass transfer. Yet, the binding capacity of proteins is high because the area of the particles is large because of their rough surface and small diameters. (6) The gel particles are covalently linked, which gives a low flow resistance, notwithstanding that the gel particles are small (0.2-0.5 mu m). (7) The bed can be compressed to decrease the distance between the gel particles and thereby increase the resolution (the method is not suitable for capillary columns, for which the monomer concentration is increased instead). The back pressure is low (often below 50 bar) even at high flow rates (100 cm/min). (8) Following compression of the bed, the resolution often is constant or even increases with an increase in flow rate, contrary to classical chromatographic theory. (9) No frit to support the bed is required in capillary chromatography, including electrochromatography, because the bed can be covalently attached to the capillary wall (a frit often disturbs the separation). (10) The recently introduced completely homogeneous continuous gel beds have the advantage that zone broadening caused by Eddy diffusion is eliminated.