Enzyme electrodes drugs

How analytical methods deal with interferences is one of the more ad hoc aspects of method validation. There is a variety of approaches to studying interference, from adding arbitrary amounts of a single interferent in the absence of the analyte to establish the response of the instrument to that species, to multivariate methods in which several interferents are added in a statistical protocol to reveal both main and interaction effects. The first question that needs to be answered is to what extent interferences are expected and how likely they are to affect the measurement. In testing blood for glucose by an enzyme electrode, other electroactive species that may be present are ascorbic acid (vitamin C), uric acid, and paracetamol (if this drug has been taken). However, electroactive metals (e.g., copper and silver) are unlikely to be present in blood in great quantities. Potentiometric membrane electrode sensors (ion selective electrodes), of which the pH electrode is the... 

In this paper we report the electrochemical polymerization of the PPy-GOD film on the glassy carbon (GC) electrode in enzyme solution without other supporting electrolytes and the electrochemical behavior of the synthesized PPy-GOD film electrode. Because the GOD enzyme molecules were doped into the polymer, the film electrode showed a different cyclic voltammetric behavior from that of a polypyrrole film doped with small anions. The film electrode has a good catalytic behavior to glucose, which is dependent on the film thickness and pH. The interesting result observed is that the thin PPy-GOD film electrode shows selectivity to some hydrophilic pharmaceutical drugs which may result in a new analytical application of the enzyme electrode. 

The concentrations of a number of analytically relevant compounds, such as creatinine, pyruvate, hormones, and drugs, are often so low that their assay with enzyme electrodes requires large sample volumes or is totally impossible. The detection limit of usual enzyme electrodes is... 

Potentiometric enzyme-based electrodes have found application in clinical, pharmaceutical, food and biochemical analyses to enable the selective determination of a wide range of important enzyme substrates, including amino acids, esters, amides, acylcholines, /Mactam antibiotics, sugars, enantioselective drugs and many others [74]. 

Polypyrrole thin film doped with glucose oxidase (PPy-GOD) has been prepared on a glassy carbon electrode by the electrochemical polymerization of the pyrrole monomer in the solution of glucose oxidase enzyme in the absence of other supporting electrolytes. The cyclic voltammetry of the PPy-GOD film electrode shows electrochemical activity which is mainly due to the redox reaction of the PPy in the film. Both in situ Raman and in situ UV-visible spectroscopic results also show the formation of the PPy film, which can be oxidized and reduced by the application of the redox potential. A good catalytic response to the glucose and an electrochemical selectivity to some hydrophilic pharmaceutical drugs are seen at the PPy-GOD film electrode. 

Electrochemical Behavior of PPy-GOD Film Electrode with Pharmaceutical Drugs. Although the chemically modified electrode has been developed for more than a decade, and many kinds of materials have been used for the modification of the electrode surface, the enzyme modified electrode has rarely been used for the study of electroactive species. This is probably due to the fact that the enzyme is not electronically conductive and also it is difficult to immobilize an enzyme on the electrode surface. So far, biological lipids have been used to modify the electrode, and the modified electrode shows a selectivity for hydrophobic molecules because the lipid molecule is hydrophobic (37-39). 

A collection of redox enzymes for which efficient DET with electrodes has been observed is given in Table 2.3. Most of them are metaUoenzymes containing iron or copper. Many of these enzymes are part of electron transfer chains, i.e., have macromolecular redox partners, or react on large substrates. The evidence for DET has not always been presented by direct electrochemical measurements. In many cases the DET has been proved indirectly by measurement of a substrate dependent catalytic current. Various metabolites ranging from sugars such as fructose, cellobiose and gluconate [6], amines like methylamine and histamine [123], lactate [91],p-cresol [93] and drugs such as benzphetamine [74] can be measured with enzymes in direct contact to an electrode. The bioelectrocatalytic reaction of peroxide is one of the most important reactions not only for the determination of peroxide(s) in various media but also substrates of coupled oxidase [8] and enzyme inhibitors [130, 252]. Furthermore, enzyme immunoassays have been developed based on DET of peroxidase and laccase and electrodes [7,131,132]. 

The DTE module (Fig. 17a) is an accessory fitting for the assay of electrolytes and can be operated in addition to the main instrument. The structure of the slides differs from that of the slides used for the assay of substances, such as drugs, enzymes or metabolites. These slides are also inscribed on each side with a code that is readable by machine and user. These slides enable the assay of electrolytes by means of single use ion-selective electrodes. 

As noted above hpid bilayer films supported on electrodes represent an interesting bioelectrochemical interface where the potentials are of the same order as those of physiological systems, and can be readily modulated. Nevertheless, this area remains less studied except in the case of enzyme complexes such CcO where the hydrophobic environment of the lipids is necessary to maintain the integrity ofthe enzyme when immobilizing it on electrodes [304, 314]. Studies of the interaction of drugs with hpid membranes are important from many points of view, particularly considering the fact that nearly 50% of drug molecules have mem-... 

Oxidation-reduction potentials are expressed in volts relative to the standard hydrogen electrode at 0 volts, and represent the tendency of a compound to lose electrons (oxidation) or gain electrons (reduction). Various enzyme systems in respiration reactions (e.g., the cytochromes) utilizing ascorbic acid, hemoglobin, as well as reactions in the Krebs cycle (succinic and fumaric acids) involve electron transfers. Drugs can affect all these systems, and the consequences must be taken into account. 

On the wider biomedical front, application of ion-selective electrodes takes in mineralised tissues, dental materials, enzyme reactions, pharmaceutical products and drug metabolism. 

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