A robust capillary electrophoresis method for the determination of organic acids in wines

Abstract

A robust capillary electrophoresis (CE) method for the determination of the six main organic acids in wines is described. The CE method is based on the use of 2,6- pyridinedicarboxylic acid (PDC) as background electrolyte (BGE) for the indirect UV detection of tartaric, malic, citric, succinic, acetic and lactic acids. Ethylenediaminetetracarboxylic acid (EDTA) was added to the BGE to eliminate interferences from trace metals on the determination of citric acid. Problems related to linearity reported in the literature using the same BGE were shown to be the result of the sample pH being lower than that of the buffer. Although this could be overcome simply by adjusting the pH of the sample, electrokinetic injection was found to be a better alternative, improving at the same time the sensitivity of the determination. Linearity over the range 100–5,000 mg/l (ppm) for all acids was achieved, requiring only 80× dilution of standards and samples prior to injection. Within day repeatabilitys (n=7) of migration times (RSD%<0.15) and peak areas (RSD%<5) as determined for a wine sample were found to be excellent. The method was applied to 20 South African wine samples, and the results are compared to data obtained by ion-exclusion liquid chromatography. Succinic acid was consistently overestimated using the latter technique, while for the other acids good agreement between the methods was noted.