Abstract: | The free solution electrophoretic mobility of a charged oligomer in an ionic solvent that approximately takes into account relaxation field effects, screening of the velocity field, and the hydrodynamic interactions resulting from motions of the charges due to an electric field is described. For double‐stranded DNA, the free solution electrophoretic mobility under ionic strengths determined by the buffer and pH conditions relevant to capillary electrophoresis increases with increasing molecular weight up to few hundred base pairs. © 1999 John Wiley & Sons, Inc. Biopoly 49: 209–214, 1999 |