Sulla determinazione polarografica delle impurezze metalliche nello zinco iperpuro

Résumé (W) On précise les conditions expérimentales les plus favorables pour l'exécution d'analyses polarographiques de zine extrêmement pur, en vue d'endéceler les impuretés, soit les éléments Cu, Bi, Pb, Cd, Tl et Fe. La méthode, très sensible, permet le dosage de ces divers métaux quand la concentration, dans le zinc, est de 0,0001% pour Pb, Bi et Tl, et de 0,00005% pour Cd, Cu et Fe.

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Zusammenfassung Es wurden die günstigsten experimentellen Bedingungen für die polarographische Bestimmung der in äußerst reinem Zink als Verunreinigungen vorkommenden Elemente Cu, Bi, Pb, Cd, Tl und Fe ermittelt.Das sehr empfindliche Verfahren gestattet die Bestimmung dieser Metalle, selbst wenn die betreffenden Konzentrationen im Zink bloß 0,0001% Pb, Bi oder Tl und 0,00005% Cd, Cu oder Fe betragen.

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Riassuno Vengono precisate le condizioni sperimentali più favorevoli per l'esecuzione dell'analisi polarografica dello zinco iperpuro per la determinazione delle impurezze di Cu, Bi, Pb, Cd, Tl, Fe.Il metodo, molto sensibile, permette il dosaggio dei varii metalli anche quando la concentrazione nello zinco è di 0,0001% per Pb, Bi, Tl e di 0,00005% per Cd, Cu, Fe.

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Epoxyfocardin and Its Putative Biogenetic Precursor,Focardin, Bioactive,New-Skeleton Diterpenoids of the Marine Ciliate Euplotes focardii from Antractica

From the ciliate Euplotes focardii, collected from Ross Sea coastal waters, Antarctica, a new-skeleton diterpenoid, epoxyfocardin, was isolated as a 85:15 mixture of hemiacetals 8a and 8b . The absolute configuration of 8a/8b was determined from Mosher's esters 11a/11b and 12a/12b . Focardin 9a/9b , most likely a biogenetic precursor of 8a/8b , was also isolated as a minor component. Focardin, and particularly epoxyfocardin, proved to be toxic towards representatives of ciliate communities from Antarctic, temperate, tropical, and equatorial environments, constituting the first example of ecologically relevant metabolites from ciliate species that inhabit polar ecosystems.     

Liquid chromatography of synthetic polymers under critical conditions of enthalpic interactions 4: Sample recovery

Reduced sample recovery is a frequent feature of LC of macromolecules under critical conditions of enthalpic interactions (LC CC). Several methods of assessment of LC CC sample recovery are compared. A novel approach is based on an online combination of the. The LC CC column with a noninteractive SEC column. It provides not only the amount but also the molar mass of the eluted/withheld polymer. The procedure was tested with poly(methyl methacrylate), bare silica gel column packings, and “critical eluent” tetrahydrofuran/toluene. It was shown that macromolecules with higher molar masses were preferentially trapped within the LC CC column packing so that the eluted part of the sample was no longer representative. The incomplete polymer elution can make the LC CC polymer analyses susceptible to significant experimental errors.     

Nonlinear vibration of a nonlocal functionally graded beam on fractional visco-Pasternak foundation

Nonlinear Dynamics - A (3+1)-dimensional coupled nonautonomous NLS model with partially nonlocal coupled nonlinearities under the linear and harmonic potentials becomes the center of attention. Two...     

Synthesis of New 2-Thiomethyl Penem Derivatives

New penem thiolesters (4-5) were synthesized and 5 was hydrolyzed. 2-mercaptomethyl penem7 is formedin situand transformed into penem monothiocarbamates9 and10.     

Dynamic stability of a nonlinear multiple-nanobeam system

Nonlinear Dynamics - We use the incremental harmonic balance (IHB) method to analyse the dynamic stability problem of a nonlinear multiple-nanobeam system (MNBS) within the framework of...