Modified electrodes with catechols

The current response of a GCE used for AMD was greatly improved after modification with polyhistidine. LOD was 6 nM for dopamine (10a), 8 nM for epinephrine (15a) and 20 nM for catechol (42). The modified electrode has also been applied for AMD after CE37. PVC membranes were designed to serve as selective barriers for the amperometric detection of phenols and elimination of thiocyanate interference . 

FIGURE 10.6. The FIA traces at poly aniline (7-min anodization, top) and polyphenol (0.5-mM phenol concentration, bottom) modified electrodes (B) to determine catechol top) and acetaminophen bottom). Corresponding traces for the unmodified electrodes are shown in (B). Traces in (a) show the response to the injection of 0.1-mM uric acid top) or NADH bottom), with traces (bMd) representing the response on adding 50-//M catechol top) or acetaminophen bottom). (From Ref. 32 with permission from Elsevier)... 

On the other hand, the detection of phenolic contaminants by developing a CNT-based DNA biosensor was reported by Zheng and co-authors [80], They immobilized DNA on a GCE modified with MWNTs dispersed in Nation (DNA/MWNTs/GCE). The DNA-modified electrode exhibited two well-defined oxidation peaks corresponding to the guanine and adenine residues of DNA, respectively. Phenol, m-cresol, and catechol owing to their interactions with DNA showed noticeable inhibition toward the response of the electrode. These biosensors obtained the detection limits of 16, 1.2, and 0.52 pM for phenol, m-cresol, and catechol, respectively. 

L.G., and Johansson, G. (1981) Catalytic-oxidation of reduced nicotonamide adenine-dinucleotide by graphite electrodes modified with adsorbed aromatics containing catechol functionalities. Analytical Chemistry, 53 (13). 1979-1982. 

FIGURE 10.7. Array response pattern obtained for flow injection of 2-//M promethazine (cross-hatch), dopamine (open), and catechol (hatch) at electrodes modified with 20-min hydrolyzed CA (1), PVP (2), Nafion (3), and lipid (4) films. The operating potential was set at 0.8 V, and the background electrolyte consisted of a 0.05-M phosphate buffer at pH 5.5. (From Ref. 124 with permission for the American Chemical Society)... 

Huo, Z., Zhou, Y., et al. Sensitive simultaneous determination of catechol and hy-droquinone using a gold electrode modified with carbon nanofibers and gold nanoparticles. MicrochimicaActa,173(l), 119-125 (2011). 

Another example of selective rejection of an interfering substance is determination of Fe + at an Au electrode modified with a mercaptodecanesulfonic acid SAM in the presence of catechol [45]. In acid solution where formation of a catechol- Fe " complex is suppressed, both species are reduced in the same potential range. However, at the SAM-modified Au electrode, the reduction current of 20 xM Fe + remains nearly unchanged in the presence of 2 mM catechol in solution. 

This move from the modification of electrodes to the modification of nonconducting surfaces in contact with electrodes is also seen in systems in which electrodes are modified using nonconduct ive particles. For example, Zak and Kuwana showed that the basic surface of alpha-alumina imbedded in glassy carbon electrodes caused catalysis of the electrooxidation of catechol and other organic species requiring loss of a proton for their oxidation JJ ), Similar results were obtained by Shaw and Creasy (78) using alumina or layered-double hydroxides in composite electrodes (vide infra). 

Selectivity Tests. In these tests, a Rank electrode was used with a single membrane layer, instead of the sandwich type of laminate. The PES, PC and its modified forms, and CA membranes were used in these tests. Hydrogen peroxide (H2O2), catechol, uric acid, paracetamol and ascorbate were used as the analytes. Each analyte was used separately. The initial concentration of the analyte was 0.2 mM. 

Lunsford, S. K., H. Choi, J. Stinson, A. Yeary, and D. D. Dionysiou, 2007. Voltammetric determination of catechol using a sonogel carbon electrode modified with nanostructured titanium dioxide. Talanta 73 172-77. 

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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