Determination of the Total Acid Content in Wine Based on the Voltammetric Reduction of Quinone

Voltammetric determination of the total acid content of wine was made by measuring the reduction prepeak current of 3,5-di-t-butyl-1,2-benzoquinone (DBBQ) due to the presence of acids in unbuffered ethanol medium. DBBQ was found to be a suitable quinone reagent for this determination with respect to its reduction potential, stability, and solubility in ethanol containing organic acids. On the voltammogram of DBBQ obtained with organic acids such as tartaric, citric, and malic acids, using a beaker-type cell and a plastic formed carbon working electrode, a well-defined single prepeak appeared, whose height was proportional to the total acid concentration, at 0.1 V (vs. a saturated calomel electrode, SCE) during the cathodic potential scan. The values of the total acid content of 23 wine samples determined by the present method were compared with those of titratable acidity obtained by the conventional potentiometric titration method. A good correlation was obtained between the results by both methods with a correlation coefficient of 0.966. The present method is superior in sensitivity and requires only one twentieth the volume of wine sample compared to the titration method.