Revisiting electroosmotic flow: An important parameter affecting separation in capillary and microchip electrophoresis

Electroosmotic flow mobility (EOF) is the movement of bulk liquid that provides an opportunity to separate charged molecules, either positive or negative, and transport all neutral molecules to the detector as a single peak. EOF originates on the silanol groups of the fused-silica capillary wall and is usually responsible for ions moving in the opposite direction of the electrostatic attraction. The interaction of the silanol groups with the electrolyte buffer leads to the formation of an electric double layer. Understanding double-layer theory and EOF is the first necessary step towards understanding many of the experimental observations in capillary and microchip electrophoresis. In this work, we introduce and validate a method to measure the EOF on both coated and uncoated capillaries by measuring the current time history, which has led to enhanced precision of the EOF measurement. We have also used the introduced method to study the fundamental parameters, such as the effect of electric field, temperature, buffer ionic strength, and pH on electroosmotic flow.