Micellar electrokinetic capillary chromatography with in situ charged micelles: II. Evaluation and comparison of octylmaltoside and octylsucrose surfactants as anionic borate complexes in the separation of herbicides

This report is an extension of our previous work involving the development of in situ charged micellar phases with adjustable surface charge density for micellar electrokinetic capillary chromatography (MECC) of neutral and charged herbicides. The micelles evaluated here are basically alkyldisaccharide‐borate complexes in which the surface charge density can be conveniently varied by changing the operating parameters such as borate concentration and/or pH of the running electrolyte. The two alkyldisaccharide surfactants (i.e., octyl‐β‐D‐maltopyranoside and octylsucrose), having the same alkyl tail but differing in the nature of the sugar polar head group, were compared and characterized over a wide range of conditions using neutral and acidic herbicides as model solutes. The effects of the operating parameters are discussed in terms of mobility, elution range parameter, capacity factor, peak capacity, and separation efficiency. The retention energetics of the micellar phases were studied using two homologous series, alkylphenylketones and alkylbenzenes. At constant micellized surfactant concentration, the two in situ charged micellar phases exhibited homoenergetic retention behavior toward the homologous solutes. On the other hand, even though the two surfactants differed by the nature of one sugar residue in their polar head groups, the micelles exhibited different hydrophobic character, with octylmaltoside yielding higher retention.