Abstract: A method of making a capillary tube for providing increased control of electroosmotic flow in electrophoretic separation. A resistive coating solution is formed so that a tube coating having a high electrical resistivity may be achieved. An electrically conductive material, such as carbon black, is homogeneously mixed with a polymer, such as polyimide, in a solvent. The content by weight of the electrically conductive material is less than 20 percent and is preferably within 7 percent to 8 percent, relative to the content by weight of the polymer. The resistive coating solution is applied to the exterior of the tube until a thickness is reached which achieves a desired resistance across the coated exterior surface. Typically, a multi-layered coating is formed. The coating solution may be applied while rotating the capillary tube or, alternatively, while the capillary tube is drawn past an applicator.