Voltammetric determination of nitrobenzene with a chemically modified carbon paste electrode. Application to wines, beers and cider

Summary A method for the determination of nitrobenzene with a sepiolite modified carbon paste electrode is presented. Nitrobenzene is adsorbed on the electrode at open circuit (pH 3.5), and determined by differential pulse voltammetry and cyclic voltammetry at pH 5.5 in 0.5 mol/l KNO₃. The calibration is linear up to 0.4 g × ml^–1. The method was applied to the determination of nitrobenzene in wines, beers and cider. The error was ±2% and the standard deviation 5%.

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Voltammetrische Bestimmung von Nitrobenzol mit Hilfe einer chemisch modifizierten Kohlepaste-Elektrode. Anwendung auf Weine, Biere und Apfelwein

     

Alkaline Activation of Metakaolin An Isothermal Conduction Calorimetry Study

The alkaline activation of metakaolin leads to high mechanical performance inorganic polymers. A JAF conduction calorimeter was used to follow the reaction of metakaolin with NaOH solutions. The alkaline activation of metakaolin to yield a cementitious material is an exothermic process involving three steps: an initial and very fast process of dissolution, which is strongly exothermic, followed by an induction period in which the heat exchange rate decreases, and finally an exothermic step of reaction reactivation in which cementitious materials precipitate and after which the heat exchange rate decreases. The calorimetric curves lead to the following findings: - The induction period is lengthened as the NaOH solution concentration and the liquid percentage increase. - The induction period is shortened as the temperature increases. - The total heat increases as the liquid percentage and the NaOH concentration increase. This revised version was published online in July 2006 with corrections to the Cover Date.     

CONSEL, a least-squares program for estimating stability constants from polarographic data

This article describes CONSEL, a least-squares linear-regression program which, when applied to polarographic data, provides estimates of stability constants suitable for priming non-linear optimization programs. The use of CONSEL avoids the need for recourse to traditional graphical methods. The results of its application to three systems are presented.     

Influence of the clay and the nickel content in catalysts for vegetable oil hydrogenation

Nickel catalysts prepared using two different clays as support, natural bentonite and palygorskite, and with different nickel contents have been tested in the hydrogenation of a sunflower oil. The influence of the clays, and of the nickel-bentonite ratio on the activity, selectivity and trans-isomer formation was investigated. Previously it was establised that no diffusional limitations were controlling the rate. Bentonite with the highest nickel content was the most active and selective catalysts.     

On the surfactant-sensitized analytical reaction of titanium with bromopyrogallol red

A spectrophotometric investigation of the Ti(IV)-bromopyrogallol red chelate shows that marked changes occur in the presence of aqueous dispersions of cetylpyridinium bromide. The increase in the absorption and the bathochromic shifts are interpreted in terms of the interaction of the binary complex Ti(IV)-BPR with the surfactant in the micelles. Analytical parameters for the spectrophotometric determination of Ti(IV) with bromopyrogallol red and cetylpyridinium bromide have been worked out in detail and are given as well. In basis of the experimental results an attempt is made to extend this approach to the understanding of the sensitized-reactions mechanism.     

Study of the nitric oxide system in the rat cerebellum during aging

Background  

The cerebellum is the neural structure with the highest levels of nitric oxide, a neurotransmitter that has been proposed to play a key role in the brain aging, although knowledge concerning its contribution to cerebellar senescence is still unclear, due mainly to absence of integrative studies that jointly evaluate the main factors involved in its cell production and function. Consequently, in the present study, we investigate the expression, location, and activity of nitric oxide synthase isoenzymes; the protein nitration; and the production of nitric oxide in the cerebellum of adult and old rats.     

Microstructural and magnetic characterization of Nd2Fe17 ball milled alloys

Microstructural and magnetic changes induced by ball milling in Nd₂Fe₁₇ alloy have been investigated. X-ray and neutron powder diffraction studies have shown that the main crystalline phase present in the as-cast Nd₂Fe₁₇ compound is the rhombohedral Th₂Zn₁₇-type crystal structure. Contrary to other materials, the crystal structure does not change after milling, and the crystal lattice parameters slightly increases while the induced strain is less than 0.1%. It has been observed from SEM and TEM images that the microstructure consists of agglomerates of nanoparticles with a mean size around 20 nm, and from magnetic measurements a broadening of the temperature range in which ferromagnetic to paramagnetic transition takes place.     

Functionalized 3,4-ethylenedithiathiophenes (EDTTs) as building blocks for poly (3,4-ethylenedithiathiophene) (PEDTT) derivatives

A convenient and straightforward procedure has been developed for the preparation of functionalized 3,4-ethylenedithiathiophene (EDTT) derivatives by using a new bromomethyl-EDTT derivative as a versatile synthon. Based on this procedure a novel EDTT derivative endowed with 9,10-anthraquinone moieties has been synthesized and electrochemically polymerized to yield a donor-acceptor PEDTT derivative.