CAPILLARY ELECTROCHROMATOGRAPHY - EFFECT OF ELECTROLYTE CONCENTRATIONON ELECTROOSMOTIC FLOW AND COLUMN EFFICIENCY

In current practice of capillary electrochromatography it is commonly assumed that the electroosmotic flow profile in a packed column is ide ntical to that in an open tube. However, this assumption may not be va lid in many cases due to thermal and double layer overlap effects. In this work, the dependence of electroosmotic mobility and plate height upon electrolyte concentration was determined for open tubular and pac ked column electrochromatography. As the electrolyte concentration inc reases over the range 0.04-1 mM, the electroosmotic mobility falls off steadily and the plate height shows a slight improvement, in the open tube. In the packed column, by contrast, the electroosmotic mobility is almost unchanged and the plate height improves dramatically with in creasing electrolyte concentration. The anomalous behavior of the pack ed column is interpreted as showing the thermal and double layer overl ap effects, probably occurring in the densely packed segments of the c olumn. (C) 1997 Elsevier Science B.V.