An Improved Capillary Electrophoresis Procedure for the Determination of Organic Acids in Grape Juice and Wine

Abstract

Major organic acids in grape juice and wine were separated and quantified by an improved capillary electrophoretic (CE) method. Indirect UV detection with 2,6-pyridinedicarboxylic acid as a background electrolyte buffer (pH 5.60) was used in this method. Although indirect UV generally uses low buffer concentrations, in this case an adequate buffer capacity was required to ensure reproducible migration times due to the pH dependency of the charge and thus mobility of the organic acids. Tartaric, malic, citric, succinic, acetic, and lactic acids were baseline resolved in 7.3 minutes by reversing the electroosmotic flow. Sample preparation was 0.45 µm filtration and a 40-fold dilution with glyoxylic acid as the internal standard. The accuracy and precision of the CE-method were better than ± 2% at 2500 mg/L. Migration time reproducibility of better than ± 1% was achieved. All acids gave linear detector responses from 5 to 125 mg/L (diluted 40-fold) with the exception of succinic (5 to 20 mg/L) and acetic (5 to 18 mg/L). This CE method enables rapid (< 13 minutes total analysis time) and simultaneous analysis of major organic acids without sample cleanup in grape juice and wine for assessing the stability of products during manufacturing processes.