In order to obtain high separation efficiencies in capillary electroph
oresis, electromigration dispersion has to be minimized either by usin
g very dilute samples in concentrated background electrolytes or by ma
tching the mobilities of the analyte and the co-ion of the background
electrolyte. A dynamic mobility matching method is presented here that
can be used advantageously in cyclodextrin-containing zwitterionic ba
ckground electrolytes. A rigorous equilibrium model has been developed
to describe the effective electrophoretic mobility of the co-ion of t
he background electrolyte as a function of the analytical concentratio
ns of the cyclodextrin, the zwitterionic buffer, and the hydronium ion
. With adjustment of these parameters, either simultaneously or indivi
dually, the co-ion mobilities can be easily varied over a 10-fold rang
e. Using fenoprofen as an example, predictions of the model have been
verified experimentally. The separation efficiency has been maximized
by varying the analytical concentration of the zwitterionic buffer whi
le the pH and the cyclodextrin concentration of the background electro
lyte were kept constant to maintain the separation selectivity. The dy
namically matched mobilities resulted in symmetric enantiomer peaks an
d good separations.