Bernard Vincke

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.

Contribution au Developpement d'Un Nouveau Modele d'Electrode: L'Electrode Bacterienne

Abstract A new type of selective electrode is proposed, based on the immobilization of bacteria on a cellulose acetate membrane. Proteus mirabilis (Urease +) is concentrated on the membrane. This electrode gives good results for urea determination, is very selective, stable during three weeks, may be regenerated after being used and is of low cost. The parameters involved in the typeof electrode manufacturing are discussed in details. Precision may be compared to the usual spectrophotometric techniques in biological media. Other types of applications will be published in a nearly future.

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.

Analytical determination of nicotinamide using bacterial electrodes

Abstract Two bacterial electrodes have been studied for the determination of nicotinamide (vitamin PP) with a linear range of 2.8 × 10 −4 M to 2 × 10 −2 M. The used strains, although taxonomicaly different and differently improved ( E. coli mutated and B. pumilus induced), present the same nicotinamide deaminase activity, able to be used for analytical assays. Their long-term stability (more than 100-fold higher than the purified enzyme) is realized by the regeneration of living cells on the electrode itself. The parameters involved in this type of electrode construction are discussed. This type of bacterial electrodes presents a very good selectivity for nicotinamide in multivitamin pharmaceutical formulations.

Efficiency of bioconversion of steroids by Fusarium oxysporum into Δ1,4-androstadiene-3,17-dione using gas chromatography

Gas-liquid chromatography is suitable for the study of the bioconversion yield of dehydroisoandrosterone into Δ1,4-androstadiene-3, 17-dione. Fusarium oxysporum (a wild isolated strain) exhibits the greatest activity for this bioreaction. The optimalization of the bioconversion efficiency has been studied in culture media or in buffered solutions using free and immobilized cells. Microbiological (cell weight, choice of strains and substrate, induction) and physicochemical (pH, temperature, ionic strength and choice of buffers, organic solvents, artificial cofactors) factors influencing the reaction yield are discussed. The same operating conditions can be used for free and immobilized cells. For both techniques, about 90% of Δ1,4-androstadiene-3,17-dione is formed in 48 h with non-induced cells and in 24 h with induced cells. A simple prototype of a laboratory bioreactor is employed and tested in order to describe the advantages and limitations.