Titrimetric method based on potentiometric titration to evaluate redox couples in wine and polyphenols
| Autor: | Vivas, N., Nonier, M. F., Vivas De Gaulejac, N. |
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| Jazyk: | angličtina |
| Rok vydání: | 2015 |
| DOI: | 10.5073/vitis.2004.43.205-208 |
| Popis: | Polyphenols are electroactive compounds, each molecule having reductive (Rd) and oxidative forms (Ox) due to the presence of several phenolic hydroxyls. Direct study of Rd/Ox forms was conducted using potentiometric titration in two steps: First, a complete reduction of the polyphenol Rd/Ox couples by titanium III chloride TiCl3 (100 % Rd), and then, oxidative titration by dichlorophenolindophenol DCPIP (100 % Ox). The second curve represents the totality of polyphenol couples titration with, for each couple, a characteristic E0 point representing the equilibrium between the concentration of Rd and Ox forms (Rd/Ox = 1). This value was typical for each polyphenol. We conducted several preliminary experiments with a model polyphenol (catechin) to establish the analysis conditions. The titration solution concentration was N/10 in HCl N and N/20 in water for TiCl3 and DCPIP respectively. The concentration of this solution diminished very rapidly, i.e. within 24 h for TiCl3 and DCPIP (under nitrogen and in darkness) and regularly needed a fresh preparation. To control the consistency and precision of the method we performed a few tests on pure products (e.g. hydroquinone/quihydrone, Fe III, Fe II, Cu II) permitting comparison between theoretical and experimental E0 values. Our result indicated less than 5 % variation and curves with a high reproducibility. VITIS - Journal of Grapevine Research, Vol. 43 No. 4 (2004): Vitis |
| Databáze: | OpenAIRE |
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