Analytical Sciences

Effects of the Molecular Properties of Mixed Solvents on the Elution of Alkyl Benzoates in RPLC

Midori YASUDA,*  Tamiyoshi SONDA,* Tomoko HIRAOKA,* Aki HORITA,** and Masaaki TABATA**

*Department of Health and Nutrition Science, Faculty of Health and Social Welfare Science, Nishikyushu University, Kanzaki-machi, Saga 842-8585, Japan
**Department of Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi, Saga 840-8502, Japan

The retention behavior and mechanism of methyl, ethyl, propyl, isopropyl, buthyl and isobuthyl benzoates have been studied at different eluent compositions of aqueous mixtures with water-soluble organic solvents (methanol, ethanol, 1-propanol, 2-propanol, acetonitrile (AN), 1,4-dioxane and tetrahydrofuran (THF)) in RPLC. The retention of the solutes is discussed based on the solvent composition, solvent polarity (E_T^N value), preferential solvation, hydrogen bonding and solvent clusters of the eluents. The smaller E_T^N values and the larger preferential solvation of the mixed solvent eluted the solutes faster. The IR spectra of HDO suggested that the solvents, except for methanol and ethanol, break the hydrogen bonding between water molecules, resulting in fast elution of the solutes. Based upon the results, we chose an optimum solvent composition for the separation of benzoates and applied it to the determination of the benzoates in clove.

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