Capillary zone electrophoresis (CZE) was used for the enantiomeric separation of (R,S)-tiaprofenic acid ([R,S]-Tia) in a pharmaceutical formulation employing an acetate buffer at pH 4.5 and 2,3,6-tri-O-methyl-beta-cyclodextrin (tri-OMe-beta-CD) as the chiral selector. The effect of the concentration of trimethylated-beta-cyclodextrin in the presence of carboxymethylated-beta-cyclodextrin (CM-beta-CD) on enantiomeric resolution of (R,S)-Tia and (R,S)-5-benzoyl-alpha-methyl-3-thiopheneacetic acid (3-isomer of tiaprofenic acid, 3-Tia) was investigated at pH 4, 4.5, and 5.