MICELLAR ELECTROKINETIC CAPILLARY CHROMATOGRAPHY WITH IN-SITU CHARGED MICELLES .1. EVALUATION OF N-D-GLUCO-N-METHYLALKANAMIDE SURFACTANTS AS ANIONIC BORATE COMPLEXES

A series of N-D-gluco-N-methylalkanamide (MEGA) surfactants was evaluated in micellar electrokinetic capillary chromatography (MECC) of neutral and charged species. The nonionic MEGA surfactants are readily converted in situ to anionic borate complexes through the association between their polyhydroxy bead groups and borate ions at alkaline pH. The MEGA-borate complex surfactants yielded micelles with adjustable surface charge density, and consequently, the magnitude of the retention window was readily altered by the pH and the concentration of borate in the running electrolyte. Studies by B-11 NMR and liquid secondary ion mass spectrometry on the borate complex formation with MEGA surfactants permitted the quantitative and qualitative determination of the various MEGA-borate complexes, respectively, and allowed the comparison of the MEGA-borate micelles to other in situ charged micelles recently introduced by this laboratory, i.e., the alkyl glucopyranoside-borate micelles. The bulky polyhydroxy head group of the MEGA-borate surfactants yielded MECC systems with unique retention properties toward neutral and charged species. At constant micellized surfactant concentration, the methylene group selectivity of various homologous series, e.g., alkylbenzenes, phenylalkyl alcohols, and phenyl alkyl ketones, was largely unaffected by the length of the alkyl tail of the surfactant, indicating a similar physicochemical basis for retention on the various MEGA-borate micellar phases. Also, when the micellized surfactant concentration was held constant, the homologous solutes exhibited homoenergetic retention with the various in situ charged micellar phases. Under the same conditions, the capacity factors of neutral solutes increased linearly with the alkyl chain length of the MEGA surfactants, indicating an increase in the hydrophobic phase ratio of the MECC systems. The MEGA-borate micellar phases were useful in the separation of a number of herbicides, polyaromatics, barbiturates, and dansyl amino acids. In addition, in the presence of small amounts of gamma-cyclodextrin, the MEGA-borate micelles allowed for the high resolution chiral separation of D,L dansyl amino acids.