A polarographic, oxygen-selective, vibrating-microelectrode system for the spatial and temporal characterisation of transmembrane oxygen fluxes in plants.

A simple procedure is described for the fabrication of micrometer to nanometer-scale platinum electrodes to be used in a vibrating oxygen-selective system. The electrode was prepared by etching a fine platinum wire and insulating it with an electrophoretic paint. The dimensions allowed this electrode to be used with the "vibrating probe technique" in exploratory studies aimed at mapping and measuring the patterns of net influxes as well as effluxes of oxygen in Olea europaea L. leaves and roots with spatial and temporal resolutions of a few microns and a few seconds, respectively. The magnitude and spatial localisation of O2 influxes in roots was characterised by two distinct peaks. The first, in the division zone, averaged 38 +/- 5 nmol m(-2) s(-1); the second, in the elongation region, averaged 68 +/- 6 nmol m(-2) s(-1). Long-term records of oxygen influx in the elongation region of the root showed an oscillatory regime characterised by a fast oscillation with periods of about 8-9 min. In leaves, the system allowed the measurement of real-time changes in O2 evolution following changes in light. Furthermore, it was possible to obtain "topographical" images of the photosynthetically generated oxygen diffusing through different stomata from a region of the leaf of 120 microm x 120 microm. The combination of topographic and electrochemical information at the micrometer scale makes the system an efficient tool for studying biological phenomena involving oxygen diffusion.

Determination of flubendazole in pharmaceutical dosage forms by differential pulse polarography and UV spectroscopy.

A precise and accurate differential pulse polarographic method was developed for the determination of flubendazole in dosage forms without any prior extraction procedure of interference from the other stated ingredients. A UV spectroscopic procedure was also described and used as reference method. Analyses were generally performed at the 4 micrograms ml-1 flubendazole level. Flubendazole or its dosage forms were dissolved in 70% perchloric acid and diluted with a pH 2.6 sodium phosphate-citric acid buffer as polarographic supporting electrolyte or spectrophotometric solvent. The peak potential occurred at about -0.9 V (vs. Ag/AgCl reference electrode), depending on the pH of the assayed solution. The irreversible electrochemical reduction involved the transfer of two electrons. The UV absorption spectrum showed a sharp maximum at 237 nm with a specific extinction coefficient of 886. No advantage was found in the use of first and second-order derivative spectrophotometry.

Determination of isosorbide-5-mononitrate in tablets by differential pulse polarography.

A differential pulse polarographic method requiring little sample separation was developed for the determination of isosorbide-5-mononitrate in tablet dosage form with the standard addition technique and without interference from common excipients. Britton-Welford buffer (pH 3.0) was used as the supporting electrolyte, the single peak occurring at -0.36 V vs. a reference Ag/AgCl electrode. The irreversible, diffusion controlled, two-electron reduction process at the dropping mercury electrode permits a precise and accurate determination of the active ingredient in the 0.4-20 microgram/ml concentration range.

The iridium/iridium oxide electrode for in vivo measurement of oesophageal and gastric pH.

An iridium-iridium oxide electrode for in vivo pH measurement of the distal oesophagus is described. It is small and flexible so it is well accepted by patients for long-term pH monitoring. The electrode also offers the possibility of including another electrode and/or a pressure sensor for simultaneous detection of two or more parameters--gastric pH or oesophageal pressure for example. A clinical study was performed on 15 healthy volunteers and the results were checked on a DGC Nova 4/S computer, showing less than 0.005% of tension in mV out of the established range in a period of 24 h pH monitoring. The volunteers' results were compared with the normal values obtained by DeMeester using a glass electrode on a similar, healthy group of American patients and no significant differences were observed. Owing to its small size, reliability, fast response to pH changes, durability and its easy storage, the Ir/IrO2 electrode is ideal for long-term pH monitoring of the upper gastro-intestinal tract.

Potentiometric titration of thiols, cationic surfactants and halides using a solid-state silver-silver sulphide electrode.

A rugged, low resistance silver-silver sulphide solid-state electrode for determining pharmaceuticals as authentic samples or in dosage forms by potentiometric titration is described. Sodium tetraphenylborate, mercury(II) acetate and silver nitrate (0.01) M were employed as titrants in the analysis of cationic surfactants (cetylpyridinium chloride, benzethonium chloride, benzalkonium chloride and chlorhexidine salts), antithyroid drugs (methimazole and propylthiouracil) or sodium halides respectively.

An iridium-iridium oxide electrode for in vivo monitoring of blood pH changes.

An iridium-iridium oxide electrode for in vivo monitoring of blood pH changes is described. Because of its small size, sensitivity, flexibility, strength and fast response, this electrode is suitable for acute implantation even in the small vessels of animals such as rats or guinea pigs, allowing continuous pH monitoring anywhere in the central arteries or veins. Excellent noise-free records have been obtained in the in vivo experiments in animals.

Preliminary experience with the pH-triggered pacemaker.

A cardiac pacemaker capable of responding to blood acidosis by change in its stimulation rate allows adjustment to a patient's metabolic needs. The blood pH is sensed by an iridium oxide electrode in the right atrium. During exercise, the venous pH decreases and the paced ventricular rate increases. If acidosis persists, the paced rate gradually returns to baseline and reaches it after about 70 minutes. A pH-triggered pacemaker has been implanted in a 72-year-old male. The pacemaker remained responsive one year after implant, increasing rate during exercise, cold pressor stress, ischemia of the arms and emotional stress.

[Clinical and biological aspects in patient with pH-triggered implanted pacemaker (author's transl)]. / Aspetti clinici e biologici in pazienti portatori di pacemaker pilotato dalle variazioni del pH ematico.

The Authors have selected the variations of blood pH to drive the pacing rate according to the new biological balance created by exercise. The clinical tests performed on the patients who have had a pH-triggered pacemaker implanted one year previously demonstrated that: a) during physical exercise there is an increase of cardiac rate triggered by the pacemaker, comparable with that noted when sinus rhythm is present; b) situations causing an increased production of cathecolamines and thus a pH variation--Cold Pressor Test, Ischaemic Test, as well as emotional stress--cause an increase of the stimulation rate of pH triggered pacemaker.

[Scanning electron microscopy study of rat lung tissue]. / Contribution a l'étude du tissu pulmonaire de rat par le microscope électronique a balayage.

Parts of rat lung tissue have been examined by means of a scanning electron microscope after either chemical or physical fixage. Chemical fixage produces retraction on the tissue structures and the alveoles appear of irregular shape. Physical fixage gives the possibility to observe lung morphology without distorsions; details reproduced are in this case very clear and in a shape which appears very close to the original conditions.

Use of an iridium electrode for direct measurements of pI of proteins after isoelectric focusing in polyacrylamide gel.

The use of an iridium microelectrode 0.5 mm in diameter is proposed for measuring the pH gradient in polyacrylamide gels after isoelectric focusing. The electrode exhibits a perfectly linear potential/pH relationship; thus it can be used directly in conjunction with a pH meter using the pH scale for readings. pH equilibrium values are rapidly reached (10-15 s) and pI determinations are obtainable with good accuracy (better than 0.1 pH).

[Effects of citidine diphosphocholine (citicholine) and phospholipids on the elastic properties of the lung and on the physico-chemical properties of the irrigation liquid]. / Effet de la citidindiphosphocholine (citicholine) et des phospholipides sur les propriétés élastiques du poumon et sur les propriétés physico-chimiques du liquide de lavage

The effect of citidin-diphosphocholine and of phospholipids treatments on the elastic properties as well as on the washing liquid physical-chemical properties of rat lungs is studied. Significant increase of the compliance and decrease of the tendency to collapse of the airways are observed after treatment with citidin-diphosphocholine.