Optimization of selectivity and resolution in micellar electrokinetic capillary chromatography with a mixed micellar system of sodium dodecyl sulfate and sodium cholate

Abstract

Selectivity and resolution were studied for the separation of seven corticosteroids by micellar electrokinetic capillary chromatography (MEKC) using a mixed micellar solution of sodium dodecyl sulfate (SDS) and sodium cholate (SC), buffered with 3-(N-morpholino)propanesulfonic acid (MOPS) or 3-[(1,1-dimethyl-2-hydroxyethyl)amino]-2-hydroxypropane sulfonic acid (AMPSO). The changes in selectivity were compared for the AMPSO-SDS-SC system by varying the pH and the concentrations of AMPSO, SDS and SC. The experimental design started with the central composite design and continued in a sequential manner. The optimum selectivity for the separation of the corticosteroids was calculated from the analyte migration times and the analyte velocities, by using empirical quadratic regression models. Satisfactory regression fits and coefficients of determination for prediction were obtained with cross-validated models. To optimize the resolution, the physical parameters of capillary length and analysis time were varied under the conditions optimal for the selectivity. In both the selectivity and the resolution, optimization the overall optimum was determined by using the desirability function technique. Analysis times were controlled by using 1,3-diaminopropane to influence the electroosmotic flow velocity (veo). The voltage was kept constant, which resulted in higher electric field strength in shorter capillaries. No changes in the selectivity were observed when 1,3-diaminopropane was used to control the electroosmotic flow velocity. Such an optimization technique, where the chemical and physical factors affecting the separation are treated independently, seemed to be effective for finding the best possible resolution for the corticosteroids.

Hydrophilic Monomethyl Auristatin E Derivatives as Novel Candidates for the Design of Antibody-Drug Conjugates

“…SDS is a well-established anionic surfactant forming spherical micelles with a hydrophobic interior and a negatively charged hydrophilic exterior. These micelles are highly hydrophobic and, thus, the selectivity for neutral, highly hydrophobic, and fairly large compounds can be poor due to their nearly complete solubilization into the SDS micelles, resulting in co-migration of compounds [20,[23][24][25]. In addition, SDS micelles are stronger hydrogen bond donors than 1-octanol and therefore they are expected to have strong interactions with hydrogen bond acceptor solutes like MMAE and its derivatives.…”

Mixed micellar electrokinetic capillary chromatography separation of depolymerized grape procyanidins

“…Mixing surfactants with different structural and polar properties to generate mixed micelles has the potential to provide variable micellar phases. Thus, by tailoring the micellar environment in this way, solute-micelle interactions can be manipulated to generate the desired selectivity [33][34][35][36]. In the current study, we develop a method that uses mixed MEKC for the fast separation of the monomeric catechins and their aminoethylthio derivatives from grape samples.…”

Modified micellar electrokinetic chromatography in the analysis of catechins and xanthines in chocolate

“…The influence of bile salts in the micellation of SDS is well documented; in particular, as shown by Wiedmer et al [30,31], bile salts provide mixed micelles in the presence of SDS. The concentration ratio between SDS and bile salt affects the hydrophobicity of the micelles and, consequently, the separation selectivity.…”

“…Applications of SDS/bile salts mixed micelles are well documented [30,31]; due to the pK a of the carboxylic group of the bile salts, their use is restricted to alkaline conditions in MEKC. In the present study, in order to evaluate the effect of incorporation of bile salts in SDS systems under acidic media, TDC, bearing a sulfate group, was considered as anionic additive in mixed SDSbased MEKC in the separation of the studied analytes.…”