Separation and Preconcentration of Biologically Active Compounds by Capillary Electrophoresis Using Imidazolium-Based Modifiers

A cationic covalent coating based on an imidazolium cation is synthesized for the inner walls of a fused silica capillary. The electroosmotic flow reproducibility, determined using dimethylformamide as a marker, was as high as 99%. The separation conditions for model systems of phenyl- and indolecarboxylic acids—phenylactic, phenylsuccinic, phenylbutanoic, indolelactic, indolepropionic, indoleacrylic, hydroxyindalmic, homogentisic, homovanillic, and hydroxyindoleacetic acids—were optimized for capillary electrophoresis. The optimal background electrolyte consisted of a 10 mM phosphate buffer solution of pH 4.2 with a 10 vol % acetonitrile additive. The resolution factors for adjacent analyte pairs ranged from 1.7 to 18.9. The synthesized coating enabled the in-capillary preconcentration of phenyl- and indolecarboxylic acids. Electrostacking increased analyte concentration factors to 106 to 512 and brought the limits of detection to 4 to 72 ng/mL.