Nonionic surfactants for improving resolution of the priority pollutant phenols by micelle-modified capillary electrophoresis

Abstract

Nonionic surfactants used as buffer additives in capillary electrophoresis improve the separation of the eleven US EPA priority pollutant phenols. A borate/phosphate buffer (pH 9.8) containing 05–2% (w/v) Tween 40 or Brij 35 surfactant gives better separation of the phenols than the same buffer with no surfactant, especially for the solution pairs 2,4-dichlorophenol/2-methyl-4,6-dinitrophenol; 2-chlorophenol/2,4-dinitrophenol; and 4-nitrophenol/2-nitrophenol. Pentachlorophenol behaves anomalously with increasing concentration of surfactant in the 0 to 0.5% range. Its net mobility is sharply reduced, and peak shape changes from the typically narrow and symmetrical CE peak to a broad, electrophoretically tailing band at a surfactant concentration near the critical micelle concentration (CMC), and then reverts to normal shape at concentrations above the CMC. Compared with CE with buffer only, the small concentrations of surfactant required to produce significant changes in selectivity have little effect on the magnitude of the electroosmotic flow or the runtime. Nonionic surfactants neither increase conductivity nor contribute to Joule heating.