Capillary electrophoretic determination of organic acids with indirect detection

Abstract

Methods for the determination of several organic acids commonly found in foods and beverages, including oxalic, citric, acetic, tartaric, malic, succinic, lactic, carbonic, aspartic, glutamic, ascorbic and gluconic acids, by capillary electrophoresis (CE) with indirect absorbance detection were developed. Several absorbance providers, including chromate, p-hydroxybenzoate, phthalate, terephthalate, trimellitate and pyromellitate, were investigated for their suitability as background electrolytes (BGEs). CE was performed in the negative voltage (reverse polarity, detector towards anode) mode. The effects of pH and various additives on CE separations were evaluated. The BGE and pH each played a major role in affecting the selectivity and resolution of CE. All analytes except malate and succinate could be baseline resolved in one run by performing CE with 5 m M trimellitate (as the BGE)-1 m M tetradecyltrimethylammonium bromide at pH 9.0 in less than 10 min. On the other hand, the CE separation of the tri- and dicarboxylic acids and hydroxydicarboxylic acids (the first five) could best be obtained at pH 5.5 in 5 min. The precision of the method for most monoprotic analytes is typically less than 1% for the migration time and 1–4% for the peak area ( n = 6). The detection limit for most analytes is of the order of 2.0·10 −6 M. The new methods developed are rapid, sensitive and quantitative and can be readily applied to real food samples for quantitative analysis.