USE OF NEUTRAL SURFACTANTS FOR THE CAPILLARY ELECTROPHORETIC SEPARATION OF HYDROPHOBICALLY-MODIFIED POLY(ACRYLIC ACIDS)

Hydrophobically modified poly(acrylic acids) (HMPAs) are random copoly mers of sodium acrylate and dodecyl acrylamide, containing 0-10% mol/m ol of dodecyl grafts. The hydrophobic character of different HMPAs of average molecular weight 150 000 was studied by capillary electrophore sis (CE), using neutral surfactants as buffer additives. The different iation of the electrophoretic mobilities of HMPAs with their hydrophob icity was achieved through the use of nonionic Brij 35 and zwitterioni c DAPS surfactants. A nearly baseline separation of the precursor and three HMPAs derivatives was obtained in a poly(ethylene glycol)-coated capillary with a background electrolyte containing 10 mM -dodecyl-N,N -dimethyl-3-ammonio-1-propanesulfonate (DAPS) and 10 mM borax (pH 9.2) . In addition to CE experiments, the polymer-surfactant interactions w ere also investigated by means of quasi-elastic light scattering (QELS ) and viscosimetric measurements. According to the latter results, the separation mechanism was interpreted as an expansion of the polymer c oil in the presence of micelles and subsequent change of its frictiona l properties. A true micellar electrokinetic capillary chromatography (MEKC) partitioning model was discarded on the basis of the relative s izes of the macromolecule and the micelles.