Binding constants for the enantiomers of modafinil with the negatively charged chiral selector sulfated-beta-CD (S-beta-CD) using CE technique is presented. The calculations of the binding constants employing three different linearization plots (double reciprocal, X-reciprocal and Y-reciprocal) were performed from the electrophoretic mobility values of modafinil enantiomers at different concentrations of S-beta-CD in the BGE. The highest inclusion affinity of the modafinil enantiomers were observed for the S-enantiomer-S-beta-CD complex, in agreement with the computational calculations performed previously. Binding constants for each enantiomer-S-beta-CD complex at different temperatures, as well as thermodynamic parameters for binding, were calculated. Host-guest binding constants using the double reciprocal fit showed better linearity (r(2) > 40.99) at all temperatures studied (15-30 degrees C) and compared with the other two fit methods. The linear van't Hoff (15-30 degrees C) plot obtained indicated that the thermodynamic parameters of complexation were temperature dependent for the enantiomers.