Computer simulations using the method of molecular dynamics have been carried out to study electro-osmosis in polar and ionic solutions. The overall objective was to model and study the separation of a variety of fluid mixtures, by electro-osmosis through semi-permeable membranes at the molecular level. The effects of direction of the external electric field on the extent of separation have been investigated. The density profiles of the components of the fluid mixtures have been reported to show adsorption near the membrane. Our results have shown the feasibility of using uniform external electric fields to enhance separation processes, such as osmosis and reverse osmosis, in polar solutions. In the past, it was generally believed that these solutions do not undergo electro-osmosis. In the case of ionic solutions, we find a similar increase, but only if the direction of the field is reversed periodically. We also show that computer simulation techniques can be a unique tool to improve our understanding of important separation processes such as electro-osmosis, which at present are not well understood. (C) 1998 Elsevier Science B.V. All rights reserved.