Separation of Neutral Compounds and Basic Drugs by Capillary Electrophoresis in Acidic Solution Using...

Working at pH 2.4 with uncoated silica capillaries has the advantage that electroosmotic flow is virtually eliminated. Excellent separations of protonated organic bases were obtained when ethanesulfonic acid was added to the running electrolyte to coat the capillary surface by a dynamic equilibrium. The effect of adding a new surfactant, sulfonated Brij-30, to the acidic electrolyte was also investigated. Use of this surfactant in acidic organic-aqueous solutions changes the elution order of many organic cations and also permits the separation of neutral organic compounds. Excellent resolution of a mixture of 19 PAHs and similar compounds was obtained in 40% organic solvent in only 20 min. The largest organic compounds form the most stable association complexes with the sulfonated Brij-30 and, thus, have the shortest migration times. It is shown that the type and concentration of surfactant, as well as the composition of the aqueous-organic solution, are conditions that can be varied over a broad range to obtain superior separations of both neutral and cationic organic compounds. The type of organic solvent is yet another condition that can be manipulated advantageously. For example, the use of equal volumes of acetonitrile and 2-propanol in water-organic solutions can give better resolution of neutral organic analytes than either solvent used alone.