Analysis of organic acids in wine by capillary electrophoresis with direct UV detection

A capillary electrophoretic method using a phosphate-based carrier electrolyte and direct UV detection at pH 6.5 for the routine determination of five organic acids in wine samples is described. The present method shows advantages over other commonly applied method based on phthalic acid buffer with indirect UV detection for the quantification of organic acids. Factors that affect capillary electrophoretic separation such as concentration and pH of the background electrolyte, concentration of the electroosmotic flow modifier, and methanol addition were considered. Separation and determination of tartaric. malic, acetic, succinic and lactic acids were achieved in approximately 6 min. The method was quantitative, with recoveries in the 98-107% range, and linear over more than one order of magnitude. The precision is better than 0.94-1.06% for migration time and 0.40-0.96% for peak area. The method is sensible, with detection limits between 0.015 and 0.054 mg L-1. The usefulness of the method was successfully demonstrated by the analysis of the considered organic acids in 39 red wines from two different Spanish Certified Brands of Origin (CBO). Determinations were made by direct injection after the appropriate sample dilution and filtration. Distributions of organic acids in Ribeira Sacra wines show a predominance of lactic (3784-452 mg L-1) and tartaric acids (1987-866 mg L-1) followed by succinic (897-398 mg L-1), malic (2844-not detected mg L-1) and acetic (749-116 mg L-1) acids. An analogous distribution was observed in the Bierzo wines: lactic acid (4037-179 mg L-1), tartaric acid (1819-772 m L-1), succinic acid (646-389 mg L-1), malic acid (1513-not detected mg L-1) and acetic acid (553-214 mg L-1). (C) 2002 Published by Elsevier Science Ltd.