Gaston Patriarche

Polarographic behaviour and degradation studies of triazolam

Abstract The electrochemical behaviour of triazolam has been determined using polarographic and cyclic voltammetric trechniques. It appears that this compound is reduced following a classical processes. A study of the hydrolytic reaction which occurs in acidic media shows that the triazole ring and the 5- o -phenyl substituent have a marked influence on the kinetics. Rate constants, half-life times, the order of the reaction and the degree of completion have been determined. The benzophenone structure of the hydrolysis product has been confirmed by 13 C NMR. Quantitative analysis has been conducted, showing that triazolam can be determined up to 1 × 10 −7 M using dp polarography.

Determination of ascorbic acid by differential pulse voltammetry

ZusammenfassungAls neues Verfahren zur Ascorbinsäurebestimmung wird die Differential-Puls-Voltammetrie mit Hilfe der Kohlepasteelektrode vorgestellt. Das Problem der Reproduzierbarkeit der Elektrodenoberfläche wurde dadurch gelöst, daß nach Konditionierung immer dieselbe Oberfläche verwendet wurde. Das Verfahren wurde zur Analyse von pharmazeutischen Tabletten und Fruchtsäften angewendet. Die Bestimmungsgrenzen liegen bei 1,5·10−7 M, 8·10−7 M und 1·10−5 M für Tabletten, dehydratisierte bzw. flüssige Säfte.SummaryA new approach to the determination of ascorbic acid has been realized with differential pulse voltammetry (DPV) on the carbon paste electrode (CPE). The problems of the reproducibility of the surface of this electrode have been resolved by using always the same surface after its conditioning. The developed method has been applied to the direct determination of vitamin C in pharmaceutical tablets and in different types of fruit juices. Limits of determination are 1.5 ×10−7 M, 8×10−7 M and 1×10−5 M for tablets, dehydrated and liquid juices, respectively.

A comparison of glassy-carbon and carbon-polymer composite electrodes incorporated into electrochemical detection systems for high-performance liquid chromatography

A comparison has been made of the performance of a novel composite carbon-polymer electrode and a glassy-carbon electrode for use as working electrodes in an electrochemical detector for HPLC. The composite electrode was found to be comparable to the glassy-carbon electrode in terms of current response, superior in terms of cost, machinability, noise levels, stabilization time and accessible potential range, and inferior in terms of the potentials required for the oxidation of certain model compounds such as epinephrine and norepinephrine.

Determination de l'Acide l-Ascorbique a l'Aide d'Electrodes Bacteriennes, Tissulaires et Enzymatiques

Abstract L-ascorbic acid membrane electrodes based upon the use of four classes of biocatalysts immobilized at an oxygen electrode are evaluated and compared in terms of electrode properties and operating requirements. Isolated ascorbate oxydase enzyme in soluble form and in covalent binding matrices, peel of cucumber and living bacterial cells of Enterobacter agglomerans strain, respectively, are employed as biocatalytic layers. The physico-chemical factors, life times and interferences are discussed in details. The low stability of the soluble enzyme sensor does not allow its analytical utilization, but the immobilized enzyme, bacterial and tissue electrodes can be used, even in multivitamin pharmaceutical formulations. The common linear range of those three biosensors are of 4.10−6 M to 7.10−4 M with a precision and a reproducibility of ± 3%.

Electrodes Potentiometriques Et Amperometriques a Levures Permeabilisees: Determination Du L-Lactate

Abstract A biosensor using permeabilized yeasts (Hansenula anomala) is described for the determination of L-lactate. The same electrode can be used either potentiometrically or amperometrically. The linear ranges are respectively of 4.10−5M to 2.10−3M for potentiometry and 8.10−7M to 3.10−3M for amperometry with a reproducibility and a precision of ± 2 to 3%. The parameters involved in the optimization of electrode response, such as pH, temperature, cofactor concentration and ionic strength of the buffers, are discussed in details for both types of measurements. The amperometric technique is suitable for lactate determinations in biological media. In this case, differential measurements are used in order to eliminate interferences of biological redox reactions.

Tentative correlation between the electrochemical oxidation of neuroleptics and their pharmacological properties

Abstract A number of drugs are largely metabolized after oral administration, especially by redox processes. Among the neuroleptics, loxapine, clotiapine and clozapine, which are seven-membered tricyclic molecules with a piperazine side-chain, are known to be extensively metabolized by oxidation. An electrochemical study of these compounds was initiated in order to determine their in vitro redox properties and to elucidate their oxidation mechanisms. The measurements were carried out in aqueous and non-aqueous media using voltammetric, cyclic voltammetric, coulometric, exhaustive electrolysis and thin-layer spectroelectrochemical techniques. The oxidation mechanisms, which differ essentially depending on the pH of the solution, are suggested. In view of these results, various similarities have been detected between the in vitro oxidation processes and the pharmacological behaviour reported in the literature. For example, the importance of the piperazine side-chain has been pointed out: oxidation no longer occurs if this side-chain is protonated; similarly, binding to the receptor is prevented if the lone electron pair of the tertiary atom is occupied. Nucleophilic additions have also been observed in non-aqueous media and the compounds have been identified using classical spectroscopic techniques. If the oxidation mechanism is identical on the piperazine chain for the three compounds, the process is somewhat different when it occurs on the tricyclic ring. Loxapine and clotiapine exhibit different behaviour from clozapine, in their electrochemical as well as in their pharmacological properties.

Comportement electrochimique anodique de divers neuroleptiques en milieu aqueux et non-aqueux

Resume Les propriðes electrochimiques dune serie de neuroleptiques possedant en commun un heterocycle central a 7 atomes avec un groupement amidine semi-cyclique, en milieu aqueux et non-aqueux ont ete examinees a laide de la voltamperometrie sur electrodes a disque de platine poli, de carbone vitreux et de pǎte de carbone, de la voltammetrie cyclique, et de la coulometrie a potentiel contrǒle. Le comportement oxydatif des trois molecules envisagees en milieu neutre aqueux et non-aqueux denote loxydation irreversible du groupement commun piperazinyl dibasique. loxydation conduisant a des composes perturbant lanalyse electrochimique probablement par formation de composes a structure polymerique. En milieu non-aqueux, laddition de deux equivalents gramme dacide perchlorique par molecule provoque la protonation du groupement dibasique. De ce fait, les courbes doxydations observees en milieu neutre disparaǐssent. Seule la clozapine diprotonee reste oxydable, mais a un potential plus positif, son comportement etant voisin de celui observe en milieu aqueux acide, loxydation se porte alors au niveau du systeme tricyclique. Ces resultats sont appuyes par des mesures obtenues en spectrometrie infra-rouge ( ir ), uv , visible et spectrometrie de masse.

Voltammetry of pharmaceuticals using different types of modified electrodes

ZusammenfassungDas elektrochemische Verhalten mehrerer chemisch interessanter Pharmazeutica an verschiedenen Kohlenstoff-Elektroden wurde mit Hilfe der cyclischen Voltammetrie untersucht. Die Eigenschaften der Kohlenstoffpaste-Elektrode und der Glaskohlenstoff-Elektrode wurden geprüft und verglichen mit denjenigen von selbst hergestellten modifizierten Elektroden auf der Basis von kolloidalem Graphit und in einem geeigneten Polymer dispergiertem Ruß. Das Verhalten des Hexacyanoferrat(II/III)-Paares wurden als typisch für einen Depolarisator angesehen. Es konnte gezeigt werden, daß das Ansprechen der Elektrode von der Art des Substrats deutlich beeinflußt wird. Die Leistungsfähigkeit jeder Elektrode wurde an Hand der voltammetrischen Kurven der verschiedenen Pharmaca ausgewertet.SummaryCyclic voltammetry was used to study the electrochemical behaviour of several chemically interesting drugs on different types of carbon based electrodes. The behaviours of the carbon paste and glassy carbon electrodes were investigated and compared with the results obtained with home-made new types of modified electrodes based on colloidal graphite or carbon black dispersed in a suitable polymer. The behaviour of the couple hexacyanoferrate-(II/ III) has been reported as a typical model of depolarizer. It has been shown that electrode responses were markedly influenced by the nature of the substrate. Performances of each electrode have been evaluated with regard to the shape of the voltammetric curves obtained during the investigation of these drugs.

Nouveau Modele d'Electrode Modifiee a Base de Carbone et de Polymere

Abstract A new type of modified electrode is proposed, based on the thermosealing of carbon and a polymer in different proportions. The mode of preparation and the performances of this new model of polymer electrode are described in details. The potential range is larger than with other electrodes, particularly in the anodic range. Some performances realized on the behaviour of pharmaceutical compounds are described.

ELECTRODE HYBRIDE POUR LA DETERMINATION DE PHOSPHATES ET DE POLYPHOSPHATES. APPLICATION AUX PROBLEMES LIES A L'ENVIRONNEMENT

Abstract The determination of phosphates and polyphosphates has been effected using an hybrid electrode, which consists of a glucose oxydase enzymic membrane and a Solanum tuberosum tissue slice. This membrane, rich in acid phosphatase, catalyses the glucose-6-phosphate hydrolysis. This reaction is quantitatively inhibited by phosphate. Several factors involved in the electrode response, like substrate concentration, pH, ionic strength and type of buffer are discussed in detail. At a 4.10−4 M glucose-6-phosphate concentration, the linear ranges of phosphates and polyphosphates are, respectively, 6.10−5 M to 1.6.10−3 M and 3.10−5 M to 1.10−3 M. The urinary phosphate contents determinated by this biosensor are in good agrement with those obtained by usual spectrophotometric techniques.