Preparation and evaluation of an imidazole-coated capillary column for theelectrophoretic separation of aromatic acids

An imidazole-coated capillary column for electrophoresis has been prepared by means of organosilanization. With mesityl oxide as neutral marker, the r esults indicated that the electroosmotic flow of the bonded phase displays a dramatic difference in pH dependence in comparison with that of the bare fused-silica column. The presence of positive charges on the coating surfac e and the anionic exchange property, due to the cationic property of the im idazole group at pH values below 6, allows the separation of geometric isom ers that are very similar in ionic mobility. Separation parameters includin g buffer composition and concentration, pH, applied voltage, and the influe nce of other additives were investigated. By using acetate buffer (100 mM, pH 5.2) and an applied voltage of -15 kV with UV detection at 212 nm, the s eparation of 11 aromatic acids including mono-, di-, tri- and tetra-carboxy lic acids could be achieved in less than 14 min. The average plate number w as 3x10(5)/m. With acetate buffer (25 mM,pH 5.5) and an applied voltage of -25 kV, the addition of silver nitrate or P-cyclodextrin significantly impr oved the resolution of some more highly charged carboxylic acids. (C) 2000 Elsevier Science B.V. All rights reserved.