SEPARATION OF DIVALENT AROMATIC ANIONS BY CAPILLARY-ZONE-ELECTROPHORESIS USING MULTIPOINT ION ASSOCIATION WITH DIVALENT QUATERNARY AMMONIUM-IONS

Positional isomers of naphthalenedisulfonate (NDS), naphthalenedicarbo xylate (NDC) and phthalate were separated using an ion association rea ction in aqueous solution followed by capillary zone electrophoresis w ith a polymer coated capillary, By using divalent quaternary ammonium ions, four NDS isomers and three NDC isomers were completely resolved, although some of the isomers were not resolved with tetrabutylammoniu m ion. Ion association constants, K-ass, between the anions and the di valent quaternary ammonium cations were also determined by analyzing t he change in electrophoretic mobility using a non-linear least-squares method. The K-ass values of the anions obtained with the divalent cat ions were larger than those with tetrabutylammonium ion because of an increased electrostatic interaction, The ion associability was also ex plained on the basis of a distance-fitting concept and the hydrophobic ity concept of the pairing cations. Ion associability was also improve d by using a better distance-fitting pairing ion. From the results obt ained, it was suggested that the charge-charge distance in cationic an d anionic molecules must be close, and the charge-charge distance of t he divalent cations was about 0.2 nm longer than that of divalent anio ns for good ion associability (a distance-fitting concept).