Analytical Sciences

Relation between Electrophoretic Behavior and Molecular Shapes of Aromatic Anions

Takashi YOKOYAMA, Hirokazu TSUJI, Takaomi AKAMATSU, and Michio ZENKI

Department of Chemistry, Faculty of Science, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan

The capillary electrophoretic behavior of 44 aromatic organic ions was investigated. The observed ionic radii (r_obs0) for the aromatic organic ions were obtained from the electrophoretic mobilities of sodium tetraborate (pH 9.2), potassium tetraborate (pH 9.2), ammonium borate (pH 9.2), and trisodium phosphate (pH 11.7) buffers with zero ionic strength. The linear relationships between the r_obs0 values and the ionic radii (r_calc), calculated by either the AM1 or PM3 method, were determined for benzyltrialkylammonium and aromatic sulfonate ions. However, the r_obs0 values were constant for the aromatic carboxylate ions in buffers, in spite of the different rcalc values. This indicates that aromatic carboxylate ions, such as benzenecarboxylate, pyridinecarboxylate, naphthalenecarboxylate, and anthracenecarboxylate ions, migrate as planar ions in buffers, whereas aromatic sulfonate ions could migrate as approximately spherical ions.

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