Analytical Sciences

Use of a Polystyrene-divinylbenzene-based Weakly Acidic Cation-Exchange Resin Column and Propionic Acid as an Eluent in Ion-Exclusion/Adsorption Chromatography of Aliphatic Carboxylic Acids and Ethanol in Food Samples

Masanobu MORI,* Takahiro HIRONAGA,* Hiroe KAJIWARA,* Nobutake NAKATANI,** Daisuke KOZAKI,*** Hideyuki ITABASHI,* and Kazuhiko TANAKA***

*Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan
**Department of Biosphere and Environmental Sciences, Faculty of Environment System, Rakuno Gakuen University, 583 Midorimachi, Bunkyodai, Ebetsu, Hokkaido 069-8501, Japan
***Graduate School for International Development and Cooperation, Hiroshima University, 1-5-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8529, Japan

We developed an ion-exclusion/adsorption chromatography (IEAC) method employing a polystyrene-divinylbenzene-based weakly acidic cation-exchange resin (PS-WCX) column with propionic acid as the eluent for the simultaneous determination of multivalent aliphatic carboxylic acids and ethanol in food samples. The PS-WCX column well resolved mono-, di-, and trivalent carboxylic acids in the acidic eluent. Propionic acid as the eluent gave a higher signal-to-noise ratio, and enabled sensitive conductimetric detection of analyte acids. We found the optimal separation condition to be the combination of a PS-WCX column and 20-mM propionic acid. Practical applicability of the developed method was confirmed by using a short precolumn with a strongly acidic cation-exchange resin in the H⁺-form connected before the separation column; this was to remove cations from food samples by converting them to hydrogen ions. Consequently, common carboxylic acids and ethanol in beer, wine, and soy sauce were successfully separated by the developed method.

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