Characterization of polymeric-mixed micelles applied as pseudo-stationary phase in MEKC

Abstract

The characterization of a polymeric mixed-micelle system applied as pseudostationary phase in micellar electrokinetic chromatography (MEKC) is presented. This system consists of sodium dodecyl sulfate (SDS), cholic acid and a polymeric tensioactive, Tetronic 1107®. This combination of the three tensioactive agents has been previously applied in a MEKC system to resolve nine steroid hormones in urine samples. In a physicochemical study of a set of test molecules and nine steroid hormones, different parameters have been calculated not only for the polymeric mixed-micelles system but also for SDS and cholic acid as single tensioactive agents and in combination. The parameters presented were micellar phase residence times, tmic, micellar proportion, tprop,mic, CLogP50 and methylene selectivity. A comparison of each parameter in the different micellar systems allowed to demonstrate that the retention and selectivity of each micellar system applied as PSP is related to the hydrophobicity of the test molecules. An exception was found in the steroid groups, where only the polymeric mixed-micelle system showed different tprop,mic values specially for intermediate and high hydrophobic steroids. The order of capability for interaction with the analytes of the studied pseudostationary phases was demonstrated by the CLogP50 values and the comparison of methylene selectivity. Moreover, cloud point and the CMC values for Tetronic were presented to complete the characterization of the polymeric mixed-micelle system. In addition, dynamic light scattering analysis and transmission electron microscopy demonstrated that the combination of SDS, cholic acid and Tetronic constitutes a polymeric mixed-micelle system.