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Reproducibility of working electrodes in voltammetry
Josypčuk, Bohdan ; Heyrovský, Michael
In voltammetry the working electrode is the source of signal from which the due information is gained. A transition from the dropping mercury electrode to any kind of stationary electrode is inevitably accompanied by worsened reproducibility of measurements, the transition to the hanging mercury drop electrode is accompanied by a certain instrumental complication. When solving a concrete task, the precision of reproducibility of measurements often becomes the decisive factor for selecting a particular type of working electrode, or for taking voltammetry as the method of choice. This work is the beginning of a wider study which includes comparison of different working electrodes and finding of optimal conditions guaranteed reproducible measurements of various electrode processes (reduction, oxidation, accumulation, adsorption and catalysis).
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Electrochemical behavior of alkali metal alcoholates on mercury
Heyrovský, Michael
In chemistry in general, and in organic chemistry and biochemistry in particular, sodium borohydride is a frequently used reducing agent of medium strength. If we follow the products of borohydride reduction by an electrochemical method, we may be surprised by the appearance on the polarization curves of current due to catalytic evolution of hydrogen.
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Voltammetric measurement of H.sub.2./sub.O.sub.2./sub. concentration in aqua-organic solutions
Kurc, L. ; Floriš, T. ; Josypčuk, Bohdan
In this work was tested the applicability of voltammetry and of meniscus silver solid amalgam electrode for determination H2O2 in presence of organic species (solvent, substrate or product of Baeyer-Villiger oxidation of cycloketones to lactones). Hydrogen peroxide can be measured in its wide concentration interval in different aqua-organic solutions. The slope of H.sub.2./sub.O.sub.2./sub. concentration dependence decreases with increasing 1,4-dioxane concentration. 1,4-dioxane in mixture with water can be used up to its concentration 80 vol. %. Model species, which represent reactants and products of Baeyer-Villiger oxidation, influence calibration dependence individually and their effect is not possible to estimate. Hence, quantitative hydrogen peroxide determination in probes of reactive mixture, which have different composition, should be carried out by standard addition method.
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The application of Brdička reaction for determination of phytochelatins in real samples of barley and thermophilic cyanobacterium grown in the presence of cadmium ions
Čížková, Petra ; Fedjuk, K. ; Šestáková, Ivana
Heavy metals represent important group of environmental contaminants. Ions of heavy metals (Cd, Pd, Cu, Hg, Zn and Ni) are released into soil solutions as a consequence of soils acidification, among others. Their presence has imminent influence on physiological procedures in plants, which have developed different mechanisms of adaptation on such conditions. One of mechanisms for plants tolerance towards heavy metal ions is their inactivation by binding on polypeptides or small proteins with high cysteine content, named phytochelatins (PC) or metallothioneins. Their function has been studied in particular at man and animals.
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Modelování spektrálních a fotochemických vlastností diiminových karbonylových komplexů přechodových kovů s diiminy
Šebera, Jakub ; Záliš, Stanislav ; Vlček, Antonín
The felxibility pf the coordination sphere of mixed valence carbonyl complexes enables to tune spectral and protochemical properties. The variety of excited states in ilustrated on Ru, Re and W mixed ligand carbonyl complexed. The lowest excited states of [W(CO)4L] and [W(CO)5L’] (L=N,N'-di-methyl-1,4-diazabutadiene, ethylenediamine, 2,2’-bipyridine, phenantroline; L’= pyridine, 4-CN-pyridine, piperidine) ckomplexes were found to be either W -> pi*(L) or W -> pi*(CO) in charakter, depending on the type of the heteroligands.
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