ELECTROPHORETIC MOBILITY STUDY OF ION ASSOCIATION BETWEEN AROMATIC ANIONS AND QUATERNARY AMMONIUM-IONS IN AQUEOUS-SOLUTION

The ion association reaction between aromatic anions and quaternary am monium ions in aqueous solutions was investigated through mobility cha nges in capillary electrophoresis. The electrophoretic mobility of aro matic anions decreased with increasing amount of quaternary ammonium s alt added to the migrating solutions. The change in mobility of anions due to the ion association was found and was treated with a least-squ ares method, giving ion association constants. The ion associability o rder of the isomers of aromatic anions was found to be naphthalene-2,6 -dicarboxylate > naphthalene-2,3-dicarboxylate, naphthalene-2-sulfonat e > naphthalene-1-sulfonate and terephthalate > isophthalate > phthala te. The order of the ion associability of naphthalene-1,5- and -2,6-di sulfonate reversed depending on the alkyl chain length of the pairing cation. The order of ion associability of quaternary ammonium ions was found to be tetraamylammonium > tetrabutylammonium > tetrapropylammon ium approximate to octyltrimethylammonium approximate to hexyltrimethy lammonium > tetraethylammonium > tetramethylammonium, and suggested th at ion association in aqueous solution was governed by the hydrophobic ity of the pairing cation.