Kinetic Study of Solute Permeation across Surfactant Micelle/Bulk Solvent Interface by Moment Analysis - Chromatographic Capillary Electrophoresis (MA-CCE)

Abstract

We applied moment analysis (MA) with chromatographic capillary electrophoresis (CCE) to the analytical determination of rate constants (kin and kout) of solute permeation at the interface between a bulk solvent and surfactant micelles. CE experiments were carried out in the MEKC system using thymol and sodium dodecylsulfate (SDS) as the solute and surfactant, respectively, under CCE conditions. In CCE mode, experimental conditions are controlled so that the migration of micelles, which dissolve single or plural solute molecules, is stopped in the axial direction of a capillary. Only solute molecules migrate in the capillary and are detected to record elution peak profiles. The mass-transfer kinetics of solute molecules in the capillary are determined from the elution peak profiles by the MA theory. The values of kin and kout were respectively determined as 1.5 × 10−6 and 2.6 × 10−9 m s−1 for the permeation of thymol molecules at the interfacial boundary of SDS micelle. It was demonstrated that MA-CCE was effective for the kinetic study of solute permeation across the interface between a bulk solvent and spherical molecular aggregates, e.g., surfactant micelles.

Moment Analysis of Mass Transfer Kinetics in Micellar Electrokinetic Chromatography Systems

“…As reported in a previous paper, 7 the following moment equations were developed for μ1 and μ2′ of the elution peaks of a solute, which were experimentally measured under CCE conditions in a CE system using spherical molecular aggregates, e.g., surfactant micelles. The derivation procedure of the moment equations is explained in detail in Supporting Information.…”

“…However, as explained earlier, we have practically measured CE data while changing the applied pressure to the capillary, because it was hard to actually conduct MEKC experiments under the CCE conditions. 7,21,22 The values of μ1 and μ2′ of the elution peaks, which had to be measured under the CCE conditions, were estimated by analyzing the CE data by a successive approximation method. An appropriate applied pressure, of which direction is opposite to that of electroosmotic flow (EOF), must be added to the capillary under the CCE conditions.…”

“…Only the representation of the axial diffusion coefficient, i.e., DL, is different between them. In a previous study, 7 the value of DL was practically derived from experimental data. In conclusion, Eqs.…”

“…In a previous paper, 7 we measured the rate constants of solute permeation at the interfacial boundary of surfactant micelles by introducing a chromatographic capillary electrophoresis (CCE) as an experimental procedure.…”

“…In a previous paper, 7 we applied the MA-CCE method for the kinetic study of permeation of thymol molecules across the interface between a bulk running buffer and sodium dodecylsulfate (SDS) micelles. It was demonstrated that the MA-CCE method was effective for an analytical determination of the permeation rate constants from a bulk solvent phase into micelles (kin) and that inversely from micelles to the bulk solvent phase (kout) at the interface of surfactant micelles.…”