Determination of citric and isocitric acids in fruit juices by capillary isotachophoresis

An isotachophoretic method was developed to determine directly citric and i socitric acids in juice samples. Isotachophoretic separations were performe d using a Villa Labeco ZK102 column-coupling isotachophoretic analyzer equi pped with a conductivity detector. The analytical capillary (160 mm x 0.3 m m I.D.) was connected with a preseparation capillary (80 mm x 0.8 mm I.D.). The leading electrolyte contained hydrochloric acid (10 mmol/l), beta -ala nine (pH 3.0), and hydroxyethylcellulose (0.1%). The terminating electrolyt e was 5 mmol/l acetic acid. Limit of quantitation for citric acid in the pr eseparation capillary was 20 mg/l and for isocitric acid in the analytical capillary was 1.2 mg/l.