Towards biomimetic electrochromatography: Fast method for the Abraham's characterization of solute-solvent interactions in micellar and microemulsion electrokinetic systems

Abstract

This study presents a fast method for the characterization of solute-solvent interactions in micellar and microemulsion electrokinetic chromatography based on the linear solvation energy relationships proposed by Abraham. The magnitude of the different types of interactions between solutes and chromatographic phases is determined from the differences in migration observed for pairs of solutes, and the effect of the different cohesion of the dispersed phase and the dispersive medium is determined from the injection of a mixture of homologous compounds, using in all injections nonanophenone as dispersed phase marker. For excess polarizability interactions (e), the compounds 8-hydroxyquinoline and 1,2-dimethoxybenzene are used. The dipolarity/polarizability coefficient (s) is assessed with 1,4- or 1,2-dicyanobenzene and 2-methylbenzaldehyde. To evaluate the solute hydrogen bond acceptor capacity (a), 3-ethoxyphenol and 2-chloroacetophenone are employed, and the hydrogen bond donor capacity (b) is characterized using 2,3,5,6-tetramethylpyrazine and 2,6-dimethylanisole. Finally, the cavity term (v) is determined using a mixture of n-alkyl phenone homologues in the range of acetophenone to heptanophenone, depending on the nature of the electrokinetic system. This fast approach allows for results comparable to the conventional methodology, which is based on the injection of a relatively large number of solutes and subsequent analysis using multiple linear regressions, but significantly reducing the time and resources invested in the characterization of electrokinetic chromatography systems. This novel method was assayed with micellar solutions prepared from bile salts (SC, SDC), anionic surfactants (SDS, LDS), and cationic surfactants (CTAB, TTAB), and microemulsions consisting of heptane, 1-butanol, and surfactants (SDS, SC, and TTAB) at different concentrations and pH values. Provided that electrokinetic chromatography has a high potential mimicking biological systems due to the availability of surfactants and cosurfactants of different natures and the wide operational pH range, this study aims to contribute to the development of biomimetic chromatography by proposing a screening method based on the Abraham's solvation parameter model, widely used in the characterization of biological systems.

Keywords: Abraham solvation parameter model; Biomimetic chromatography; Chromatographic selectivity; EKC; Electrokinetic chromatography; Linear solvation energy relationships; MEEKC; MEKC.