Optimization of Particle Dimensions for High Efficiency in Capillary Electrochromatography

An experimental study has been performed on electroosmotic flow (EOF) development in packed columns for CEC. The intraparticle EOF velocities have been measured, relative to the interstitial fluid velocity, with particles of various pore size and solutions of various ionic strength. Based on the experimental findings, the optimal particle diameter and pore size have been predicted for CEC with respect to speed (EOF velocity) and separation efficiency.Suitable EOF may be created through columns packed with particles as small as 20 nm in diameter. However, to take advantage of the flat flow profile, particles of 80 nm in diameter or larger can be used. A high perfusive EOF may be generated with pore sizes as small as 5 nm, although a pore size of 30 nm may be optimal with respect to pore-to-interstitial flow ratio, required ionic strength, and separation efficiency. It is argued that this pore diameter may also be optimal for the flow channels in monolithic/continuous columns in CEC with respect to separation efficiency. However, when axial diffusion and thermal effects are taken into account, the optimal particle diameter for CEC may be much larger than that following from just considering the EOF development. To limit axial diffusion in columns with 80-nm-diameter particles, the electrical field strength should be >106 V/m, which is much higher than can be applied with commercial equipment. When considering field strengths that may be applied with present instrumentation, the optimal particle diameter for CEC is in the order of 0.5-1.0 (mu)m. The combination of the required high field strengths and high ionic strengths sets limits to the column diameter in order to prevent significant band broadening due to thermal effects. When columns packed with particles of the specified dimensions can be effectively operated in CEC, plate numbers well over 106 may be generated in short times.