Amperometric Selectivity

The electrochemical oxidation of NO around 1.0 V (cf. Table 1) has recently been used to devise NO-selective amperometric microprobe electrodes to detect its release in biological tissues [20, 21]. In aqueous solution, NO is quickly air-oxidized to NO2. Surprisingly, the kinetics of this reaction have not been investigated. In the gas phase at room temperature, NO is rapidly oxidized by oxygen (AG° = — 70.54 kJ/mol) in a third-order mechanism [8] ... 

A cell with a small Pt disk working electrode coated with a polyelectrolyte multilayer made of poly(allylamine)-poly(vinyl sulfate), a Pt wire counterelectrode and a reference SCSE may be used for selective amperometric determination of H2O2, in the presence of ascorbic acid (22), uric acid (29) and acetaminophen (148). The latter three compounds show a significant response with the bare working electrode at +0.6 V while a practically nil one with the coated electrode. The reason for this selectivity may be an exclusion effect by the coating. ... 

I.M. Christie, P.H. Treloar and P. Vadgama, Plasticised polyCvinyl chloride) as a permselective barrier membrane for high-selectivity amperometric sensors and biosensors, Anal. Chirm. Acta, 269 (1992) 65-73. 

Of particular relevance to chemical sensor technology are the novel results of the electrochemical competition experiments. When an equimolar mixture ofNa+/K+orNa + /K + /Mg2 + cations is added to electrochemical solutions of (26), the ferrocene/ferricinium redox couple shifts anodically by an amount approximately the same as that induced by the K+ cation alone. This observation, together with the FABMS competition experimental findings, suggests that (26) is a first-generation prototype potassium-selective amperometric sensor, capable of detecting the K+ cation in the presence of Na+ and Mg2+ ions. 

Choline oxidase and acetylcholineesterase Enzymes immobilized on a nylon net attached to H202-selective amperometric sensor. ChO is used for choline and AChE and ChO for acetylcholine. Rectilinear response in the range of 1-10 pM. Response time 1-2 min. Interferences occur from ascorbic acid, primary amines, and most seriously from betaine aldehyde. [64]... 

Porphyrins are often employed in sensors on account of their ability to act as cation hosts and, with a suitable metal ion coordinated, as redox catalysts. Electropolymerised poly(metalloporphyrin)s have been used as potentiometric anion-selective electrodes [131] and as amperometric electrocatalytic sensors for many species including phenols [132], nitrous oxide [133] and oxygen [134]. Panasyuk et al. [135] have electropolymerised [nickel-(protoporphyrin IX)dimethylester] (Fig. 18.10) on glassy carbon in the presence of nitrobenzene in an attempt to prepare a nitrobenzene-selective amperometric sensor. Following extraction of the nitrobenzene the electrode was exposed to different species and cyclic voltammetric measurements made. A response was observed at the reduction potential of nitrobenzene (the polyporphyrin film acts only to accumulate the analyte and not in a catalytic fashion). Selectivity for nitrobenzene compared with w-nitroaniline and o-nitroto-luene was enhanced compared with an untreated electrode, while a glassy carbon-... 

Potentiometric electrodes of all types In flow-injection analysis (FIA) glass, ion-selective, amperometric electrodes, etc., can all theoretically be used in a detector cell to quantify some chemical substance. 

FIG. 7 Approach curve of a H202-selective amperometric tip electrode towards a polymer layer loaded with GOx. The tip was produced by immobilizing horseradish peroxidase onto the cross section of an insulated carbon fiber of 7 /xm diameter. Solution composition 1 mM glucose in air-saturated 0.2 M phosphate buffer, pH 7. (From Ref. 22. Copyright 1993 American Chemical Society.)... 

Modification of the electrode started with academic studies on physical and chemical adsorption, i.e., with the appearance of fundamental researches on adsorption of different species on electrode surfaces, both under polarization and at open circuit potential [3]. The properties of similar chemically modified electrodes , in which the modifier consists of a monolayer of a variety of chemical species with different characteristics, possessing (or not) particular properties, were initially studied in a purely electrochemical context, aimed at the collection of fundamental physico-chemical data. A small group of electrochemists were among those involved in these basic studies, envisioning the perspectives opened by the novel systems. In the first, really fascinating, work with similar monomolecular layers, cobalt porphyrin and phthalocyanine, as well as deliberately synthesized dicobalt face-to-face porphyrins were adsorbed on Pt or C surfaces to catalyze molecular oxygen reduction [4]. However, similar systems were not always used or adequately tested in proper amperometric sensing by researchers more interested in electroanalysis dicobalt face-to-face porphirins still constitute a rare example of tailored materials for selective amperometric detection. 

Koryta reported the first FIT reaction in 1979 (25), and this method can not only provide the stoichiometric information between the ion and the ligand, thermodynamic and kinetic parameters, but can also have applications in selective amperometric ion sensors, and in electro-assisted solvent extraction across liquid membranes (1, 2, 6, 62). Various ionophores, such as crown ethers, antibiotics, ETH series ionophores and calixarenes, have been used to facilitate cations transfer (1-6). Recently anion transfers facilitated by ionophores have also been observed (63, 64). 

High-Pressure Liquid Chromatography. - A new sensitive, selective amperometric detector has been developed, based on the oxidation in alkaline solutions of carbohydrates on a glassy carbon electrode onto which has been cast copper/copper oxide particles dispersed in a Nafion film. This system substantially lowers the overpotential for oxidation. Its use was demonstrated for the quantitation of various aldoses, sugar alcohols, and disaccharides in h.p.l.c. and flow injection analyses. ... 

Selective amperometric microelectrodes are also obtained from a microinterface between two immiscible electrolyte solutions (ITIES) formed at the tip of a glass micropipette. These micro-ITIES behave as disk UME and allow the quantitative amperometric detection of different ions based on ion-transfer voltammetry. A K+-selective micro-ITIES successfully imaged the transport of K+ across a 50 pm diameter pore by SECM. ... 

Lei Y, Mulchandani P, Wang J, Chen W, Mulchandani A (2005) Highly sensitive and selective amperometric microbial biosensor for direct determination of p-nitrophenyl-substituted organophosphate nerve agents. Environ Sci Technol 39 8853-8857... 

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