Jean-Claude Viré

Square-wave adsorptive stripping voltammetry of menadione (vitamin K3)

Menadione (vitamin K(3)) undergoes a reversible two-electron transfer involving the quinone structure in acidic medium. As demonstrated by using cyclic voltammetry, the reduced form is more strongly adsorbed than the oxidized one. Stripping voltammetry of an adsorbed layer has been applied to the determination of this molecule after preconcentration of the reduced compound and scanning the potential towards less negative values. Adsorption, which is highly effective when stirring is used, approaches an equilibrium process in quiescent solution, as evidenced by a loss of part of the adsorbed material when stirring is stopped. A square-wave mode has been selected owing to its high sensitivity (the current is 20 times that for the differential pulse mode), but also to its high scan-rate, which minimizes the slow desorption process occurring during the scan. A concentration range from 2 x 10(-10) to 5 x 10(-7)M is easily investigated, the detection limit being 1.3 x 10(-10)M. The influence of several operational parameters has also been considered.

Applications of polarography and voltametry in analysis for drugs

Abstract Recent developments and applications of polarographic and voltammetric techniques in drug analysis are reviewed. Typical applications to pharmacologically active compounds are described.

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.

Comparative study of three polymeric membrane electrodes selective to tizanidine

Abstract Three types of polymeric electrodes were using a poly(vinyl chloride) film plasticized with a dioctyl phthalate-nitrobenzene mixture and containing an ion pair of the drug tizanidine. The membrane of the so-called conventional electrode, which includes an internal Ag/AgCl reference, was immobilized on a micropipette tip. A single-layer electrode was prepared by coating a graphite rod with the membrane, while the graphite rod of a two-layer electrode was previously coated with a poly(4,4′-biphenol) film before the sensitive membrane was deposited. These electrodes exhibit a Nernstian response in the concentration range 5 x 10 −6 −1 x 10 −2 M with a slope between 55 and 57 mV per decade. The response is not affected by pH between 3 and 7. The influence of several parameters involved in the construction of these electrodes on their lifetime is discussed, the highest durability being observed for the conventional electrode. Selectivity coefficients against various organic and inorganic cations were evaluated. The conventional electrode was applied to the determination of tizanidine in drug formulations using direct potentiometry.

Identification Des Produits De La Reduction Electrochimique d'Un Nouvel Antiinflammatoire: Le Piroxicam

Abstract The electrochemical reduction of piroxicam has been investigated on a mercury pool in acidic and alcaline media. After exhaustive electrolysis, the extraction followed by chromatographic separation of the reaction products gives the reduced compounds which have been identified by spectroscopic techniques. From the analysis of the NMR 1H, 13C and IR spectra and the results of our preceding electrochemical investigation, the polarographic behaviour of piroxicam has been elucidated. The process occurs by the irreversible reduction of the double bond of the enol function over the total pH range investigated. However, in alkaline and highly acidic solutions, a preceding two-electron step occurs, giving rise to the opening of the thiazine ring.

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.

Barium ion-selective electrode based on a new neutral carrier complex

Abstract Three derivatives of a new class of ionophores belonging to the binaphthyl polyethers and exhibiting high lipophilicity were synthesized and evaluated as neutral carriers for the fabrication of a barium ion-selective electrode. The influence of the length of the ether side-chain and of the substitution of the amido group ending this side-chain on the complexing capability of barium ion is discussed. The ion-selective membrane was constructed by incorporating the selected ionophore in an ethylene-vinyl acetate copolymer which was previously dissolved in tetrahydrofuran. Nitrophenyl octyl ether was used as a plasticizer and a small amount of sodium tetraphenylborate was added as a lipophilic anion. The influence of the nature of the plasticizer and of the amount of incorporated ionophore on the characteristics of the electrode is discussed. The response of this electrode is linear in the range 0.1–3 × 10 −6 M with a slope of 30 mV per decade. The potential is not affected by pH modifications in the range 1.6–8. 1. Selectivity coefficients determined for both monovalent and divalent cations show negligible interference from most of them. The electrode exhibits excellent potential stability and an operational lifetime of more than 5 months. Moreover, this electrode is not poisoned by copper(II) ions, in contrast with an ion-exchanger liquid membrane electrode, which exhibits a potential shift, or with a PVC membrane electrode, which requires in this instance a long recovery time. This electrode was applied successfully to the determination of sulphate ions in commercial mineral waters using potentiometric titration.

Comportement Polarographique d'Un Nouvel Agent Cytostatique: La Carminomycine

Abstract Carminomycin, a new cytostatic agent related to the anthracyclin group, has been investigated using D.C., A.C., D.P. polarography and cyclic voltammetric techniques. Two reduction waves have been reported, one concerning the quinonic function, the other being devoted to the carbonyl group located in C13. Some important adsorption phenomena may interfere in a large pH range. The detection limit is 8. 10−6 M (D.P.P.).

Electrochemical behavior of zopiclone

The electrochemical properties of zopiclone, an anxiolytic and hypnotic drug, have been investigated by different techniques. The compound is reduced in two 2-electron steps in the pH range 0-12. The first step, which corresponds to the reduction of the pyrazine ring, is reversible in acidic and neutral solutions. Strong adsorption phenomena accompany the reduction process in acidic and neutral media. Zopiclone can be quantitatively measured over the entire pH range using DC polarography. However, the use of differential pulse and square-wave modes for quantitative measurements is more limited due to a slope modification in the current-concentration relationship. Adsorptive stripping voltammetry can be applied to the determination of low levels of the drug at pH 9, but only short deposition times may be used because large amounts of material accumulated under stirring conditions due to fast adsorption kinetics are rapidly released from the electrode surface. Detection limits are 1 x 10(-7)M and 2 x 10(-10)M for polarography and adsorptive stripping voltammetry, respectively. Only the first wave is of analytical interest for both techniques.

Etude Polarographique De La Marcellomycine

Abstract Polarographic study of marcellomycine. d.c., a.c. and d.p. polarography and cyclic voltammetric techniques were used to investigate the electrochemical properties of marcellomycine. These are found to be quite similar to those of aclacinomycine or carminomycine, the main reversible two-electron wave being attributed tot he reduction of the quinonic structure. The molecule undergoes a degradation process starting in acidic medium and giving rise to the formation of two small irreversible waves at more negative potentials. This process is time, illumination and pH dependent. Important adsorption phenomena interfere in the investigated pH range but are lowered in very acidic medium. Quantitative measurements have been carried out at pH 1 and 6 in a 10−3 to 10−5 M concentration range using d.c. polarography. d.p. technique allows determinations in a restricted 10−5 to 10−4 M range. A detection limit of 1 · 10−5 M has been fixed at pH 1.