Analytical Sciences

Abstract − Analytical Sciences, 30(9), 919 (2014).

Analysis of Ion-association Equilibrium of Precipitable Dipicrylaminate Ion in Aqueous Solution by Capillary Zone Electrophoresis
Toshio TAKAYANAGI,* Kinuyo OGURA,** and Tomoki YABUTANI*
*Department of Life System, Institute of Technology and Science, The University of Tokushima, 2-1 Minami-josanjima, Tokushima 770-8506, Japan
**Faculty of Engineering, The University of Tokushima, 2-1 Minami-josanjima, Tokushima 770-8506, Japan
The ion-association equilibrium of the dipicrylaminate ion (DPA) was investigated in an aqueous solution with alkali metal ions and with its 18-crown-6 ether complexes as pairing cations by capillary zone electrophoresis (CZE). Although DPA is precipitable with the pairing cations of K+ and Cs+ in a homogenous aqueous solution, a low concentration of DPA below its solubility suppressed the formation of the precipitates, and DPA was detected as a usual CZE signal. Changes in the electrophoretic mobility of DPA was analyzed for its ion-association equilibrium. The ion association constants determined were almost comparable among alkali metal ions, while the ion association constants were meaningfully large with a hydrophobic 18-crown-6 ether complex of K+. The CZE separation was also proved to be useful for the equilibrium analysis under precipitating conditions. It was suggested that the precipitable property of DPA with K+ and Cs+ could not be attributed to the ion-association process in an aqueous solution, but to the condensation process concerning the intermolecular CH···O bond in the precipitate crystals, as reported.