The determination of the organic acids, tartaric, malic, citric, lactic, succinic, and acetic, by capillary electrophoresis was investigated. The acids were separated on a polyethyleneimine (PEI)-coated capillary filled with 20 mM 6-aminohexanoic acid and 5 mM 2,4-dihydroxybenzoic acid and adjusted to pH 4.9. The anodic electroosmotic flow generated by the PEI coating favors the separation speed of organic acids. The method was applied to the determination of organic acids in white wine and fruit juices. (C) 1999 John Wiley & Sons, Inc.