The applicability of the classical semiempirical relationships between the electrophoretic mobility and charge-to-mass ratio (m, versus q/M-alpha) has been investigated to describe migration behavior of a series of quinolones in aqueous and hydroorganic media The Stoke's law (alpha = 1/3), the classical polymer model (alpha = 1/2) and the Offord's surface law (alpha = 2/3) were evaluated in the pH range comprised between 2 and 11 in ACN-water mixtures of 0, 10 and 30% m/m. ACN As accurate acidity constant values were available for charge calculations, correlations were excellent The results obtained using the Offord's surface law were slightly better and the plots of q/M-2/3 against the separation electrolyte pH were used to select the optimum pH valises for separation of a quinolone mixture. The electropherograms simulated considering the accurate charge-to-mass ratio of each quinolone at the selected pH values were in good agreement with the experimental results. The ability of these relationships to predict the separation of the studied quinolones at a certain pH value in methanol-water and THF-water mixtures was also demonstrated.