a) The cyclic voltammogram of catechin, a polyphenol found in wine, was recorded

Question

a) The cyclic voltammogram of catechin, a polyphenol found in wine, was recorded in aqueous solution in buffer and in the presence of SO2 (see scans (i) and (ii) above). Why does the current decrease in scan (i) as the voltage scans from 400 mV to 600 mV?

b) Why is the current much higher in scan (ii) as the voltage scans from 400 mV to 600 mV?

c) Is the E?’ for SO4-2 -> HSO3- more positive than +400 mV, less positive than +400 mV or about the same as +400 mV?

11. In a recent article about measuring naturally occurring phenols in wine (O. Makhotkina, P.A. Kilmartin / Analytica Chimica Acta 668 (2010) 155-165) a group of researchers demonstrated that sulfur dioxide (in the form of HSO3) reacts readily with quinones OH HO HO OH OH catechin (mM) So. CH,COH 4 (ii) I .:-.. (iv) (iv) 1 (v) I (vi) I 2 (v) - solid curve (vi) - dashed curve 0.1 mM catechin 400 600 200 Potential / mV (Ag/AgCI)

Explanation / Answer

By the formation of SO2 in the scan (ii), this reagent is more conductive than the CH3COH. So that, the presence of SO2 in this case produces a increases of current and the voltage scans going from 400mV (i) to 600 mV(ii).

The electroactive reagent is decrease in the neighborhood of the electrode surface so, when the potential takes the value of slightly less than 0.1 V due to cathodic reduction intensity develops . Then you can see a rapid increase in intensity as the reagent concentration decreases to be close to the electrode surface .

The intensity of the peak is due to two components : one is the initial intensity necessary to adjust the surface concentration of reactant to its equilibrium concentration given by the Nernst equation and the second is the intensity diffusion controlled .

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.