Catechol coated electrode

When a PNVP-coated electrode is placed in a solution containing a catechol compound, the concentration of the catechol analyte in the polymer film increases with time as the polymer begins to complex the analyte. Figure 4 compares the cyclic voltammetric response obtained in a 1.00 mM solution of dihydroxyphenylacetic acid (DOPAC) at a PNVP-coated electrode (top) and a bare graphite electrode (bottom). DOPAC is one of the... 

Other researchers have demonstrated the utility of Nafion-coated electrodes for the exclusion of ascorbate from the electrode surface during the determination of protonated (cationic) catecholamines (31,32). Although the rejection of ascorbate by these coatings is substantially superior to that demonstrated by PNVP coatings, Nafion films function on the basis of ion-exchange. For this reason, negatively-charged catechol compounds are rejected with anionic interferents such as ascorbic and uric acids. PNVP... 

We now examine a specific problem, the electrooxidation of catechol at a Nafion-coated electrode containing dispersed RUO2 particles. This work was recently published by Lyons and coworkers. Typical cyclic voltammograms recorded for the Ru02/Nafion composite material in 0.2 M H2SO4 are shown in Fig. 2.33. The broad nature of the current response across the entire potential window examined... 

The redox electrochemistry of a Fe /Fe couple is easily accomplished on a phthalocyanine-coated electrode with peak separations comparable to that of platinum [141,142,163,164]. Phthalocyanine-coated electrodes are found to be efficient electrocatalysts to catalys catechol, p-benzoquinone and oxalic acid oxidations [120,150]. The electrochemical activity of these electrodes may be due to the high voltage, surface area, high electronic conductivity and redox behaviour of phthalocyanine, vanadium phthalocyanine and other phthalocyanines have been prepared by vapour deposition and show photoelectrochemical responses when dipped in aqueous electrolytes [244-249]. Polymeric phthalocyanines of Co and Fe are coated on active carbon and are shown to give catalytic properties for dioxygen reduction and thiol oxidations. Dioxygen chemisorption and ammonia absorption of metallo... 

Electrodes modified by eiectrodeposited 3-methylPT can be used as chemical sensors for organic and especially biological interesting molecules. The modified surfaces catalyze the oxidation of several compounds (e.g. ferrocyanide, catechol, ascorbic acid, hydroquinone, dopamine, epinephrine, acetaminophene, p-aminophenol, and reduced nicotinamide adenine dinucleotide). The sensitivity of these polymer-coated electrodes is 4 to 10 times higher than pure electrodes of platinum. Binary and also ternary mixtures can also be analyzed these electrodes are also suitable as an amperometric detector for flow injection analysis [211, 212]. 

In the present case this was determined to be is = 0.88 mA cm 2 for a substrate concentration of 1 mM from the intercepts of Koutecky-Levich plots for the oxidation of L-dopa at electrodes coated with identical PVP films to those used for the mediation experiments but which contained the non-mediating surrogate anion Fe(CN)63 instead of IrCle - in an effort to preserve morphology. The values of is for other substrate concentrations were calculated from the relevant equation in Figure 2. In favourable cases (see the mediated oxidation of catechol at a Nafion-Fe(bipy)3 coated electrode below), two distinct waves corresponding to direct and mediated reactions may be observed which greatly facilitates the deter- mination of is. 

Mediated oxidation of catechol at a Nafion-Fe(bipy)3 + coated electrode... 

Liu, A. and E. Wang. 1994. Determination of catechol derivatives on pretreated and copolymer coated glassy carbon electrode. Talanta 41 147-154. 

Equation 3 indicates that for redox-polymer mediated reactions that comply with "SR kinetics, fast mediator-substrate cross-reaction rates (large ik) and poor substrate permeation through the polymer phase (low is) will tend to decrease the thickness of the reaction zone. Situations may thus arise in which only the outermost layers of mediator sites attached to the coating participate in the reaction with substrate. Such a surface process is observed for the oxidation of catechol at a carbon electrode modified with a Nation film containing Fe(bipy)3 + as mediator. The homogeneous solution rate constant for the oxidation of catechol by Fe(bipy)3 is estimated a to be 2 x 10 and is roughly 1000 times... 

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