Characterisation of electroosmotic flow in capillary electrochromatography columns

Currently available capillary electrochromatography (CEC) instrumentation using UV-Vis detection dictates the use of duplex columns. Due to discontinuities (electric field strength and conductivity) that arise at the boundary between the packed and open sections in these columns, the determination of the electroosmotic flow (EOF) is complicated. Thiourea has been found to be an accurate EOF marker under the conditions employed in this study. By injecting this compound onto a fully packed column and comparing the obtained mobilities with those calculated from measured zeta potential values a value for tortuosity has been obtained. The use of laser Doppler velocimetry (LDV) for the measurement of zeta potential has been found to be the most direct and rapid method of characterising silica support materials in terms of electroosmotic mobility. The open section in duplex CEC columns has been shown to influence the actual column flow-rate. The EOF measured using duplex columns of varying packed and open section lengths have been compared with those obtained for a fully packed column.