Evidence of an EC’ mechanism occurring during the simultaneous assay of ascorbic and uric acids on poly(3,4-ethylenedioxythiophene) modified gold microsensor

New Insight into the EC’ Mechanism of Uric Acid Regeneration in the Presence of Ascorbic Acid on a Poly(3,4‐ethylenedioxithiophene) Modified Gold Electrode

“…The addition of 10 −3 mol L −1 AA in the previous solution induced not only the appearance of an additional irreversible oxidation peak located at −0.06 V corresponding to AA oxidation, but also a significant amplification of the previous anodic peak current (dashed line), getting from 18.75 to 24.2 μA. This enhanced signal agreed well with an EC’ mechanism resulting from a chemical reaction coupled to the electrochemical step as previously highlighted , where UA is regenerated at the vicinity of the electrode surface by reaction between its oxidized form and AA.…”

“…The electrode surface was modified using an electropolymerized poly (3,4‐ethylenedioxythiophene) (PEDOT) film which strongly adheres on most electrode materials, shows high conductivity in its oxidized state and presents a good stability in aqueous electrolytes and a biocompatibility with biological media . We also demonstrated for the first time that the UA oxidation current increased in the presence of AA, in agreement with a coupled electrochemical / chemical catalytic mechanism . This EC’ mechanism is of great importance for clinical analysis in normal physiological conditions as it induces a systematic error in UA concentration.…”

Simultaneous Assay of Ascorbate and Urate Antioxidants in Human Blood Serum Using PEDOT- Based Electrochemical Microsensor

“…It is noteworthy that the sensitivity was sensibly higher for UA than for AA. This difference resulted not only from the specific interactions of each antioxidant with the polymer as previously discussed; it was also the consequence of an EC' mechanism resulting from a chemical reaction in solution coupled to the electrochemical step [58] as demonstrated previously in our laboratory with synthetic aqueous solutions containing a mixture of AA and UA [59]. The apparent standard potential of the (ascorbyl radical/ascorbate ion) redox system being lower than that of the (alloxan/urate) one (0.28 V and 0.59 V at pH 7.0, respectively [60,61]), a spontaneous oxidoreduction reaction between AA and the UA oxidation product takes place, thus regenerating the reduced form of UA at the vicinity of the modified electrode surface.…”

“…The apparent standard potential of the (ascorbyl radical/ascorbate ion) redox system being lower than that of the (alloxan/urate) one (0.28 V and 0.59 V at pH 7.0, respectively [60,61]), a spontaneous oxidoreduction reaction between AA and the UA oxidation product takes place, thus regenerating the reduced form of UA at the vicinity of the modified electrode surface. Consequently an obvious change was observed in the sensitivity of the microsensor for UA oxidation current depending on whether AA was present in the sample or not [59]. This phenomenon was never considered before certainly because AA was in most studies in excess compared to UA.…”

Electrochemiluminescence of Tris(2,2′-bipyridyl)ruthenium(II) with Ascorbic Acid and Dehydroascorbic Acid in Aqueous and Non-aqueous Solutions

“…Ascorbic acid (H2A) is a reduced form of vitamin C that is an effective antioxidant and radical scavenger. [7][8][9] It will be oxidized to ascorbyl radical anion (A • -), an intermediate in weak basic conditions, and then to dehydroascorbic acid (DHA, oxidized form of vitamin C) via a two-electron and one-proton oxidation process. [10][11][12] Figure 1 shows the chemical structures of H2A, its monoanion (HA -) and its possible oxidative products.…”