Capillary electrophoretic studies on the migration behavior of cationic solutes and the influence of interactions of cationic solutes with sodium dodecyl sulfate on the formation of micelles and critical micelle concentration

Abstract

The migration behavior of cationic solutes and influences of the interactions of cationic solutes with sodium dodecyl sulfate (SDS) on the formation of micelles and its critical micelle concentration (CMC) were investigated by capillary electrophoresis at neutral pH. Catecholamines and structurally related compounds, including epinephrine, norepinephrine, dopamine, norephedrine, and tyramine, which involve different extents of hydrophobic, ionic and hydrogen-bonding interactions with SDS surfactant, are selected as cationic solutes. The dependence of the effective electrophoretic mobility of cationic solutes on the concentration of surfactant monomers in the premicellar region provides direct evidence of the formation of ion-pairs between cationic solutes and anionic dodecyl sulfate monomers. Three different approaches, based on the variations of either the effective electrophoretic mobility or the retention factor as a function of surfactant concentration in the premicellar and micellar regions, and the linear relationship between the retention factor and the product of a distribution coefficient and the phase ratio, were considered to determine the CMC value of SDS micelles. The suitability of the methods used for the determination of the CMC of SDS with these cationic solutes was discussed. Depending on the structures of cationic solutes and electrophoretic conditions, the CMC value of SDS determined varies in a wide concentration range. The results indicate that, in addition to hydrophobic interaction, both ionic and hydrogen-bonding interactions have pronounced effects on the formation of SDS micelles. Ionic interaction between cationic solutes and SDS surfactant stabilizes the SDS micelles, whereas hydrogen-bonding interactions weakens the solubilization of the attractive ionic interaction. The elevation of the CMC of SDS depends heavily on hydrogen-bonding interactions between cationic solutes and SDS surfactant. Thus, the CMC value of SDS is remarkably elevated with catecholamines, such as epinephrine and norepinephrine, as compared with norephedrine. In addition, the effect of methanol content in the sample solution of these cationic solutes on the CMC of SDS was also examined.

Voltammetric analysis of epinephrine using glassy carbon electrode modified with nanocomposite prepared from Co-Nd bimetallic nanoparticles, alumina nanoparticles and functionalized multiwalled carbon nanotubes

“…Hence, there is a requirement to develop an efficient technique for EP detection in different biological fluids (Oruch et al 2014 ). Several conventional methods have been used for EP determination and were based on high performance liquid chromatography (Sabbioni et al 2004 ), fluorimetry (Cañizares and de Castro 1995 ), capillary electrophoresis (Lin et al 2004 ), chemiluminescence (Michałowski and Hałaburda 2001 ) and electrochemical analysis (Garrido et al 1997 ; Ni et al 1999 ).…”

Comparison of the retention of basic compounds in anionic and cationic microemulsion electrokinetic chromatographic systems

“…In the case of basic compounds, the retention mechanism into the SDS microemulsion can be more complex. The literature reports some studies based on micellar electrokinetic chromatography (MEKC) where an electrostatic interaction is observed when compounds and surfactant present opposite charges [11,13,[20][21][22]. Indeed, Quang et al obtained higher retention factors (k) for the ionized bases than for the neutral compounds, meaning that apart from hydrophobicity other equilibria, such as ion pairing, must exist, enhancing retention of cationic ionized bases [13].…”