Faradaic reactions at glassy carbon surfaces studied by coulometric stripping potentiometry

摘要

Coulometric stripping potentiometry has been used for the quantitative determination of Faradaic reactions on glassy carbon surfaces. Exhaustive cathodic electrolysis in samples (10 mu L) containing known amounts of Bi-III, Cu-II, Pb-II or Cd-II, subsequent stripping of the amalgamated atoms with a constant oxidative current, and evaluation of the amount of metal ions, using Faraday's law, frequently yielded too high values. For example, when electrolyzing a sample containing 100 mu M of Cu-II at -1.60 V a value of 109 mu M was obtained, the corresponding value at an electrolysis potential of -0.90 V being 101 mu M. The discrepancies were attributed to re-oxidation of electroactive surface groups, reduced during cathodic electrolysis, simultaneous with the oxidation of the amalgamated elements. As expected, it was found that this interference was more pronounced the more cathodic the electrolysis potential. The kinetics of the re-oxidation was studied revealing half times in the order of 0.4 to 0.6 ms. An oxygen to carbon surface atomic ratio equal to 0.08 was found assuming that ail electroactive groups contained oxygen and one electron per oxygen atom was involved in the oxidation. [References: 15]