Nation-coated electrode

Matsue et al. [19] recommended an electrochemical determination method using Nation coated electrodes for the determination of electroinactive medicines. Acetylcholine was determined voltammetri-cally with the use of a Nation 117-coated vitreous carbon working electrode and a saturated calomel electrode. The method is based on competition between (ferrocenylmethyl) trimethylammonium ion and the drug cations for entry into the Nation layer. The presence of acetylcholine caused a decrease in the peak current for (ferrocenylmethyl) trimethylammonium ion, from which the acetylcholine concentration is determined. The method was described to have permitted the determination of 1 pM-1 mM of acetylcholine. 

Surface modified NO sensors incorporate an electrode surface that has been modified or treated in some way so as to increase the selectivity of the sensor for NO and promote catalytic oxidation of NO. An early example of such a sensor was presented by Malinski and Taha in 1992 [27], In this publication an —500nm diameter carbon fiber electrode was coated with tetrakis(3-methoxy-4-hydroxyphenyl)porphyrin, via oxidative polymerization, and Nation. This electrode was shown to have a detection limit of — lOnM for NO and great selectivity against common interferences. However, recently it has been shown that this electrode suffers severe interference from H202 [28],... 

Figure 17-26 Electron micrograph of the tip of a Nation-coated carbon fiber electrode. The carbon inside the electrode has a diameter of 10 ixm. Nafion permits cations to pass but excludes anions. /Photo courtesy R. M. WigMman. From R. M. Wightman. L. J. May, and A C. Michael. Detection of Dopamine Dynamics in the Brain, Anal. Chem. 1988, 60. 76VA ]...

Earlandite structure, 849 Electrical conductivity metal complexes, 133 tetracyanoplatinates anion-deficient salts, 136 Electrical properties metal complexes, 133-154 Electrocatalysis, 28 Electrochemical cells, 1 Electrochemistry, 1-33 hydrogen or oxygen production from water coordination complex catalysts, 532 mineral processing, 831 reduction, 831 Electrodeposi (ion of metals, 1-15 mineral processing difficulty, 831 Electrodes clay modified, 23 ferrocene modified, 20 nation coated, 15 polymers on, 16 polyvinylferrocene coated, 19 poly(4-vinylpyridine) coated, 17 redox centres, 17 Prussian blue modified, 21 surface modified, 15-31 Electrolysis... 

E.V. Gc ol, G.A. Evmgyn, J.L. Marty, H.C. Budnikov, and V.G. Winter, Amperometric biosensors based on Nation coated screen-printed electrodes for the determination of choUnesterase inhibitors. Talanta 53,379-389 (2000). 

Naegeli, R. Redepenning, J. Anson, F. C. Influence of supporting electrolyte concentration and composition on formal potentials and entropies of redox couples incorporated in Nation coatings on electrodes. J. Phys. Chem. 1986, 90, 6227-6232. 

It was found that the dissociation rate constant is dependent on the concentration of the complexing agent L if a hanging mercury drop electrode was used. For small values of c, kd = 90s At Nation coated mercury film electrode the value of k is lower, k = 6 s . The difference has been explained by the assumption of adsorption of proline anions on the bare mercury electrode surface. This effect induces the acceleration of the dissociation process. 

Figure 1. A. Cyclic voltammograms recorded with a Nafion-coated pyrolytic graphite electrode containing 1.1 x 10" mole cm of sulfonate groups. The solid line was obtained witn the Nation coating alone the dashed line resulted after incorporation of 2.2 x 10" ° mole cm of CoP(py)4 in the coating.

In a recent development ultramicroelectrodes were used to obtain charge transfer diffusion cofficients for electroactive polymer films. Whiteley and Martin used chronoamperometry at Nation ionomer-coated electrodes to quantify the diffusional transport of ions in the polymer matrix. The experiment is simple in execution. The potential of the ionomer-coated ultramicrodisc electrode is stepped from a value where no redox activity occurs to one where the oxidation or reduction rate of the immobilized redox species is diffusion-controlled. Provided the diffusion layer within the film created by the potential step is always... 

To prepare the working electrode layer, the electrode active material such as carbon or pseudocapacitive materials are mixed with conductive carbon and isopropanol for 30 to 60 min to form an ink. A desired amount of this ink (several microliters for a small electrode surface area such as 0.2 to 0.5 cm ) is pipetted gradually onto a prepolished electrode with a microsyringe. After drying, several microliters of diluted Nation solution is used to cover the coated electrode to form a uniform electrode layer for electrochemical measurements. 

Xu, H., Zeng, L Huang, D. et al. (2008) A nation-coated bismuth film electrode for the determination of heavy metals in vegetable using differential pulse anodic stripping voltammetry an alternative to mercury-based electrodes. Food Chem., 109,834-839. 

A necessary step in conducting these measurements is preparation of the WE. A well-developed procedure for electrode preparation is described by Mayrhofer et al. [3]. A small amount of catalyst power (Pt- or Pt alloy-based catalyst) is first mixed ultrasonically with deionized water, followed by the addition of alcohol or isopropanol ( 1.0 ml alcohol to 5 mg catalyst) and 5 wt.% Nation ionomer solution (-1/40 volume ratio with the alcohol) to form a well-mixed catalyst ink. Then a small amount of catalyst ink is pipetted and coated onto a disk electrode surface such as GC or gold electrode, with a geometric area of 0.2-0.5 cm. The coated electrode is then left to air dry. The total catalyst loading on a GC electrode can be adjusted to 0.02-0.2 mg cm . ... 

Another way to prepare the electrode is to make a catalyst ink that does not contain Nation ionomer solution. The ink is pipetted and coated onto the GC or gold surface, and then, the required amount of Nafion ionomer solution is dropped onto the top of the catalyst coating to form a catalyst layer coated electrode. 

Nation is a perfluorosulfonated ion-exchange polymer and has received a great deal of attention as a modifier for polymer-coated electrodes mainly because of its outstanding chemical stability and excellent ionic conductivity. Nafion-coated electrodes have been proved to be effective for the determination of electroactive compounds " . The attractive features of Nafion which are useful for electroanalytical purposes are its preconcentrating ability sof cations and its ionic selectivity. 

Tang, Q., Shan, Z., Wang, L., Qin, X., Zhu, K., Tian, J., Liu, X., Nation coated sulfur-carbon electrode for high performance hthium-sulfur batteries. J. Power Sources 2014, 246 (0), 253-259. 

The Nation coating must protect the underlying sensor elements from compounds in the body, selectively transport O2 relative to glucose, and should preferably inhibit interfering species such as ascorbic acid (2,7J-7J). The permeability of Nation to several compounds was determined using a Nafion-coated rotating disk electrode (79). From plots of the inverse of the observed disk current as a fiuiction of the inverse of the square root of the rotation rate (a Koutecky-Levich plot) the permeability. Pm, was obtained. This value was determined for a series of Nation thicknesses, measured by ellipsometry, and the effective diffusion coefficients were obtained, according to equation 1. 

Describe the rationale of using electrodes coated with Nation films for selective detection of the cationic neurotransmitter dopamine in the presence of the common interference from anionic ascorbic acid. 

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