Micellar electrok1netic capillary chromatography with in situ charged micelles. vii. expanding the utility of alkylglycoside-borate micelles to acidic and neutral ph for capillary electrophoresis of dansyl amino acids and herbicides¹

Micellar electrokinetic capillary chromatography (MECC) using micelles based on alkylglycoside-borate complexes, i.e., in situ charged micelles, was demonstrated over a wide range of pH including acidic media. The surfactants used in this study were of the alkyl-jV-methylglucamide (MEGA) types that possess a linear sugar moiety as the polar head group. These surfactants showed the ability to complex with borate even at acidic pH, thus expanding the pH range over which in situ charged micelles can be used in MECC. The electrokinetic behavior of the MEGA-borate micelle at acidic and neutral pH using relatively high borate concentration was different than that observed at alkaline pH using lower borate concentration. These studies which were performed at high borate concentration suggested the formation of polyborates which increased the ionic strength and viscosity of the running electrolyte without further increasing the surface charge density of the micelle. This led to decreasing the electrophoretic mobility of the micelle and the electroosmotic flow with increasing borate concentration. The net result was an increase in the migration time window at increasing borate concentration. Moreover, the magnitude of the migration time window could be adjusted by varying the pH of the running electrolyte over the pH range from 3.5 to 9.0. The MEGA-borate systems proved useful for the separation of phenoxy acid herbicides and their esters, urea herbicides, dansyl amino acids and aromatics.