Colorimetric Determination of Tartaric Acid in Wine

Abstract

Research indicated a need for improvement in existing methods of measuring tartrate levels in wine. These studies showed considerable disagreement among most investigators with regard to: the colorimetric method to be used, the location of the peak absorption, and whether to read absorption at this peak or along its slope. This study resolves these questions and optimizes the reaction mechanism involved in the analysis. Experiments indicated that these results could be achieved with a modification of the colorimetric method introduced by Matchett et al. Many of the components inherent in wine influenced the colorimetric reaction. Removal of the color by activated charcoal did not separate these, and in fact introduced additional error. Further studies proved that these interferences could be separated by column chromatography. Wine is added to an anion-exchange resin charged with acetate anion. The tartrate ion is eluted off using sodium sulfate. Other carboxylic acids in wine behave similarly, and since they interfere with the colorimetric reaction the eluate had to be fractionated. Color for the tartrate-metavanadate reaction is maximum at 480 nm. Maximum color development takes 80 minutes and lasts for an hour. The method uses a 25-ml portion of the 45th through the 75th-ml fraction, 0.5 ml of glacial acetic acid, and 2.0 ml of 3% sodium metavanadate. The sample is compared with a sodium sulfate blank prepared similarly. Presented additionally is an accurate method for lactic acid determination. This method is that of Barker and Summerson as modified by Pilone and Kunkee. This procedure gives reproducible results with excellent recovery of added concentrations of both acids from wine.