Capillary electrochromatography with macroporous particles

The performance of macro-porous particles in capillary electrochromatograph y is studied. Three reversed-phase stationary phases with pore diameters be tween 500 Angstrom and 4000 Angstrom have been tested for separation effici ency and mobile phase velocity. With these stationary phases, a large porti on of the total flow appears to be through the pores of particles, thereby increasing the separation efficiency through a further decrease of the how inhomogeneity and through enhancement of the mass transfer kinetics. The effects of pore size and mobile phase composition on the plate height a nd mobile phase velocity have been studied. With increasing buffer concentr ations and larger pore diameters, higher mobile phase velocities and higher separation efficiencies have been obtained. Columns packed with 7 mu m particles containing pores with a diameter of 40 00 Angstrom generated up to 430 000 theoretical plates/m for retained compo unds. Reduced plate heights as low as 0.34 have been observed, clearly demo nstrating that a significant portion of the flow is through the pores. For the particles containing 4000 Angstrom pores no minimum was observed in the H-u plot up to linear velocities of 3.3 mm/s, suggesting that the separati on efficiency is dominated by axial diffusion. On relatively long (72 cm) c olumns, efficiencies of up to 230 000 theoretical plates/column have been o btained under non-optimal running conditions. On short (8.3 cm) columns fas t separations could be performed with approximately 15 000 theoretical plat es generated in less than 30 s. (C) 1999 Elsevier Science B.V. All rights r eserved.