Pseudo-stationary phases with sodium dodecyl sulfate (SDS) as an anionic surfactant, Tween 20 as a nonionic surfactant or SDS-Tween 20 mixed micelles were examined to control the separation and migration behavior of four acidic compounds similar in structure, including ketoprofen, naproxen, sulindac and indometacin in micellar electrokinetic capillary chromatography ( MECC). Various parameters such as type of micelles, surfactant concentration, buffer pH and ethanol as organic modifier that affect the separation were studied. Complete separations of these acidic drugs were respectively achieved in SDS, Tween 20 or mixed micelle system. The retention time of solutes was the longest in SDS system and the shortest in Tween 20 system, and the elution order was reversed each other. The retention time of analytes increased with increasing surfactant concentration in the SDS or Tween 20 system. In the mixed micelle system, the total surfactant concentration was kept constant and large differences in selectivity were achieved by changing the micellar mole fractions. The resolution of analytes became worse as the buffer pH increased from 6. 2 to 7.6. The addition of ethanol exerted a strong effect not only on flowing phase but also on micellar phase, so the capacity factors of the analytes changed differently with the increase of the ethanol concentration. The hydrophobicity of analytes played a significant role in the influence on the separation behaviors in the MECC systems. At last, in the two systems of SDS-MECC and Tween 20-MECC, the contents of sulindac and indometacin in tablets were determined and satisfactory results were obtained.

Key words: electrokinetic chromatography, MICELLE, STATIONARY PHASE, SDS, TWEEN 20