THEORETICAL ASPECTS ON THE REGULATION OF ELECTROOSMOTIC FLOW IN CAPILLARY ELECTROPHORESIS BY ADDING CHARGED AMPHIPHILES

The regulation of electroosmotic flow (EOF) in capillary electrophores is is of great importance in many analytical applications. In this pap er, the variation of EOF with the concentration of amphiphile is studi ed by adding a charged amphiphile to the background electrolyte (BGE) when using a C-8-coated capillary. A theory relating the change in con centration of amphiphile in the BGE to the variation in observed EOF i s presented, The basis of the theory is that the adsorbed amphiphile c reates an electrostatic surface potential that is calculated from the linearised Poisson-Boltzmann equation, The adsorption isotherm of the amphiphile to the capillary surface is described by an electrostatic s urface potential modified linear isotherm. By assuming that the zeta-p otential in the Smoluchowski equation is proportional to the electrost atic surface potential, an equation describing the EOF as a function o f amphiphile concentration is obtained. The proposed theory is experim entally tested by adding octane sulfonate, tetrabutylammonium or tetra pentylammonium ion to the BGE. It is shown that, in these cases, the p roposed theory describes the EOF as a function of amphiphile concentra tion well and that, as expected, the proportionality constant between the electrostatic surface potential and the zeta-potential is less tha n one. Some practical aspects and problems that occur with this type o f measurement are also discussed. (C) 1997 Elsevier Science B.V.