Separation and determination of di- and tricarboxylic acids in fruits by capillary zone electrophoresis with amperometric detection Original Research Article

The method for separation and determination of several di- and tricarboxylic acids, including oxalic, malic, tartaric and citric acids (OX, MA, TA and CI), found in fruit juices by capillary zone electrophoresis with amperometric detection at a copper electrode was developed. Based on cyclic voltammetry (CV) experiments, the detection mechanism for the analytes at a copper electrode was proved to be the formation of complexes between di- and tricarboxylic acids and Cu(II) ion on the electrode surface. Separation was carried out in a pH 6.2 phosphate buffer solution (PBS) containing 0.4 mmol/l cetylpridinium bromide (CPB) and 20 mmol/l β-cyclodextrin (β-CD) as an electro-osmotic flow (EOF) modifier to reverse the direction of the EOF and a complexing reagent for CPB to improve the separation, respectively. At the working potential of 0.12 V (versus SCE), the calibration curves for the analytes were linear with about three orders of magnitude and the detection limits (S/N=3) for them were between 4 and 8 fmol. By the method developed here, di- and tricarboxylic acids in four fruit juices, apple, grape, pear and orange juices, were successfully separated and determined.