Some considerations concerning the composition of the mobile phase in capillary electrochromatography

In capillary electrochromatography (CEC) the propulsion of the mobile phase is effected by electroosmosis. The velocity of the electroosmotic dow is d ependent on surface properties of the stationary phase and on bulk properti es of the mobile phase. Therefore, in CEC the optimization of the mobile ph ase composition must take more factors into account than in pressure-driven LC. In this paper, the impact of the electrolyte concentration in the mobi le phase and of the volume fraction of the organic mobile phase constituent on the velocity of the electroosmotic how and on the chromatographic effic iency is investigated for CEC with capillaries packed with octadecylsilica gel. Bias of the data by an open section of the capillary has been excluded by employing completely packed capillaries and detection in a packed secti on. Acetonitrile as organic constituent of the mobile phase is compared to other possible organic modifiers (polar organic solvents) concerning influe nce on velocity of the electroosmotic flow and retention of solutes. (C) 20 00 Elsevier Science B.V. All rights reserved.