Characterization of a microemulsion system with AOT as pseudostationary phase in MEEKC for the analysis of estrogens

Abstract

Microemulsion electrokinetic chromatography (MEEKC) is an electrodriven separation technique, which employs a microemulsion (ME) as pseudostationary phase (PSP) in capillary electrophoresis. In recent years, MEEKC has become an important tool for achieving the separation of a diverse range of solutes. Microemulsions are composed of nanometer-sized oil droplets suspended in aqueous buffer, which is commonly referred to as oil-in-water ME. The aim of this work was the characterization of a ME based on sodium bis(2-ethylhexyl)sulfosuccinate (AOT) as pseudostationary phase, developed for the simultaneous determination of natural and synthetic estrogens by MEEKC. The ME system consisted of 1.4% w/w AOT,1.0% w/w octane, 7.0% w/w 1-butanol and 90.6% w/w 20 mM sodium salt of 3(cyclohexylamino)-2-hydroxy-1-propanesulfonic acid (CAPSO) and 10 mM phosphate buffer at pH 12.5. The AOT MEEKC system was characterized electrophoretically, physicochemically and morphologically and parameters such as microdroplets phase residence times (tmic) and microdroplets proportion (tprop,mic) were calculated for the first time in order to study the interaction between the solutes and the PSP. In order to characterize the AOT microemulsion regions, a phase diagram was constructed, and two regions, a W/O and another O/W were determined. Dynamic viscosity was determined and dynamic light scattering and transmission electron microscopy were performed to complete the characterization of the PSP.