Moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model to analytically determine the rate constant for the interfacial solute permeation from a bulk solvent into molecular aggregates (kin) and the inverse rate constant from the molecular aggregates to the bulk solvent (kout). The moment equations were in good agreement with those derived in a different manner. To demonstrate their effectiveness in one concrete example, the moment equations were used to analytically determine the values of kin and kout of three electrically neutral solutes, i.e. resorcinol, phenol, and nitrobenzene, from the first absolute (μ1A) and second central (μ2C) moments of their elution peaks, as measured by electrokinetic chromatography (EKC), in which the sodium dodecyl sulfate (SDS) micelles were used as a pseudostationary phase. The values of kin and kout should be determined with no chemical modifications and no physical action with the molecular aggregates because they are dynamic systems formed through weak interactions between the components. The moment analysis of the elution peak profiles measured by EKC is effective to unambiguously determine kin, kout, and the partition equilibrium constant (kin/kout) under appropriate experimental conditions.

DOI: https://doi.org/10.1002/elps.201900182 The cover picture shows the schematic illustration of the kinetic study on solute permeation at the interface of spherical molecular aggregates. Moment theory was used to analytically determine the rate constants of the interfacial solute permeation (kin and kout) and partition equilibrium constant (Kp) from the first absolute and second central moments of elution peaks measured by electrokinetic chromatography (EKC). The moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model. The values of kin and kout of electrically neutral solutes were simultaneously determined in the EKC system, in which sodium dodecylsulfate micelles were used as one example of spherical molecular aggregates.