Abstract
The voltammetric behavior for the reduction of acetic and perchloric acid was studied with a platinum microdisk electrode in synthetic ethanol-water mixtures with an ethanol content of 40 and 50 vol.%. The results demonstrated that the reduction of acetic acid proceeds through a fast chemical reaction preceding the electrode transfer involving hydrogen evolution, as in water solutions, the dissociation constant of the acetic acid being greater than about 1×10−6. This allowed us to derive an analytical expression relating the steady-state limiting current and analytical concentration of the weak acid. Depending on the concentration level, either standard addition procedures or an absolute equation proved valid to quantify the acid content of the synthetic mixtures. The detection limits evaluated in the synthetic 40 and 50 vol.% ethanol-water mixtures, provided 1.92×10−5 and 2.15×10−5 M, respectively. The voltammetric procedure was applied to the determination of the total acid content in distilled beverages such as whisky, rum, vodka and grappa, having an ethanol content ranging from 38 to 50 %. The results obtained with the proposed method were compared with the AOAC official method, which requires a dilution of the sample in water, and a good agreement was found. Comparative measurements carried out directly in the real samples by acid-base titrations using either phenolpthalein dye or potentiometry with a glass electrode for end-point detection, gave unreliable results.
Published Version
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