DYNAMICS OF CAPILLARY ELECTROCHROMATOGRAPHY - EXPERIMENTAL-STUDY ON THE ELECTROSMOTIC FLOW AND CONDUCTANCE IN OPEN AND PACKED CAPILLARIES

For capillary electrochromatography (CEC) to become an analytical sepa ration technique of high speed and resolution the factors determining the conductivity of the column as well as the generation and control o f electroosmotic flow (EOF) in porous media have to be understood. In the present study the conductance of capillaries packed with a variety of stationary phases was evaluated with respect to the conductance of the open capillary and the data were interpreted in the light of the Tobias equation. However, the consistently observed reduction of the E OF when a capillary having a charged inner wall is packed with particl es having charges of the same sign and the dependence of the EOF veloc ity on the particle size needs further explanation. The data suggests that, due to the employment of relatively long columns packed with sma ll particles, CEC may offer peak capacities much higher than HPLC or m icro-HPLC. The CEC columns are unique as they consist of a packed and an open capillary segment having different conductances and consequent ly different voltage gradients and electrical field strengths. Therefo re, any sufficiently detailed study on CEC systems requires also the c haracterization of the individual column segments. EOF velocities of 6 -7 mm/s could be realized at 60 kV applied voltage with a 23/32 cm x 5 0 mu m raw fused-silica capillary packed with 6-mu m Zorbax ODS partic les. The current was a linear function of the field strength up to 1.8 kV/cm, but at high field strengths the EOF increased with squared hel d strength. Data on band spreading indicate that with a given column t he plate height at high EOF velocities is smaller in CEC than in micro -HPLC and it is weakly dependent on the velocity. (C) 1997 Elsevier Sc ience B.V.