Separation and Analysis of Theran Volcanic Glass by INAA, XRF and EPMA

 Pumice from the “Minoan eruption” on Thera (Cyclades, Greece) was investigated to reveal the differences between the composition of the bulk material, which contains a certain percentage of crystallites, and the pure glass phase. This is important for the identification of vitric tephra layers found in the Eastern Mediterranean region in archaeological context and in deep sea drilling cores. Eruption products, deposited at some distance, have usually lost their crystalline fraction due to gravity separation and consist only of glass shards. Only major element distributions in such layers and in pumiceous glass phases have been published up to now, but these data are not sufficient for a reliable identification of the volcanic source, as several other eruptions are known to have produced chemically very similar layers in this region (Milos, Nisyros, Yali, Kos). Therefore, a technique has been developed to separate the glass phase from the primary pumice to reveal differences in the trace element distributions obtained by instrumental neutron activation analysis (INAA). X-ray diffractometry and microscopical techniques were applied to check the purity of this fraction. The concentrations of the major constituents, in particular Al, Ca, Fe, K, Mg, Mn, Na, Si, and Ti were determined by X-ray fluorescence (XRF) and electron probe microanalysis (EPMA), those of Al, Ba, Ca, Ce, Co, Cr, Cs, Dy, Eu, Fe, Hf, K, La, Lu, Mn, Na, Nd, Rb, Sb, Sc, Sm, Ta, Ti, Th, U, Yb and Zr by instrumental neutron activation analysis and partly also by X-ray fluorescence. Subtle differences between the compositions of the glass phase and the bulk material are explained by differentiation during partial crystallization and their applicability to the classification of tephra layers is demonstrated.     

Quantitative Extraktion von Blei und Zink als Verbindungen der Diphenylarsinsäure

Analytical and Bioanalytical Chemistry - Es wird über die Möglichkeit berichtet, die Metalle Blei und Zink mit Hilfe von Diphenylarsinsäure als Reagens und Chloroform als...     

Miscibility and interactions of polystyrene/polyolefine and polystyrene/poly(n-alkyl methacrylate) mixtures in dilute xylene solutions

The miscibility and intermolecular interactions between polystyrene (PS) and poly(ethylene-co-propylene) (EPC), as well as between PS and long-chain poly(alkyl methacrylates) (PAMA), namely, poly(dodecyl methacrylate) (PDDMA) and poly(octadecyl methacrylate) (PODMA), in dilute xylene solutions at 30 °C were studied. Investigated polymers are widely used as rheology modifiers, i.e. viscosity index improvers and pour point depressants for lubricating mineral oils. The specific and reduced viscosities of two- and three-component polymer solutions as well as intrinsic viscosities and Huggins’ parameter values were determined as functions of the polymer mixture composition and overall polymer concentration. The reduced viscosity was found to be linearly dependent on the overall polymer concentration. The observed viscosities of polymer mixtures were intermediate to those of the mixture constituents; the values decrease in the order: EPC > PS > PAMA. The specific viscosities of all the polymer mixtures obtained as the experimental results and calculated applying the Catsiff-Hewett and Krigbaum-Wall theoretical equations were considered. Since all the polymer/polymer pairs showed the negative viscometric interaction parameter values (Δb₁₂ < 0), the PS/EPC and EPC/PAMA mixtures were found to be immiscible. The observed repulsive molecular interactions originate from the differences in polymer composition and molar masses. This conclusion was supported by calculations employing the group contribution approach of Coleman, Graf and Painter. The calculated values of interaction parameters for (co)polymer blends, Λ₁₂, were 5.47, 6.42 and 13.1 J cm⁻³ for PS/PDDMA, PS/PODMA and PS/EPC, respectively.     

Triphenylarsinoxid als analytisches Reagens

Zusammenfassung Es wird über die analytischen Eigenschaften von Triphenylarsinoxid im Hinblick auf Fällungs- und Extraktionsmethoden berichtet. Fällungen können mit Uranyl- und Wismutionen aus stark saurer Lösung vorgenommen werden. Neben Uranyl, Wismut, Thorium und Cer(IV) lassen sich mit diesem Reagens noch die Anionen Chromat, Vanadat sowie der Rhodan- und Chlorokomplex des Eisens(III) mit Chloroform extrahieren. Die Zusammensetzung der Uranyl- und Wismutverbindungen wird mitgeteilt und Formeln werden vorgeschlagen.

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Summary A report is given of the analytical properties of triphenylarsine oxide with regard to precipitation and extraction methods. Precipitations can be carried out with uranyl and bismuth ions from strong acid solution. In addition to uranyl, bismuth, thorium and cerium (IV), the chromate and vanadate anions as well as the thiocyano and chloro complex of iron (III) can be extracted with this reagent. The composition of the uranyl and bismuth compounds is given and formulars are suggested.

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Résumé On communique les propriétés analytiques de l'oxyde de triphenylarsine du point de vue des méthodes de précipitation et d'extraction. On peut effectuer les précipitations par les ions uranyle et bismuth sur la solution fortement acide. En présence d'ions uranyles, de bismuth, de thorium et de cérium-IV, on peut aussi, avec ce réactif, extraire par le chloroforme les anions chromate et vanadate ainsi que le complexe rhodié et chloré de fer-III. On communique la composition des composés avec les ions uranyles et bismuth et l'on propose des formules.

     

Coding and ordering Kekulé structures

The concept of numerical Kekulé structures is used for coding and ordering geometrical (standard) Kekulé structures of several classes of polycyclic conjugated molecules: catacondensed, pericondensed, and fully arenoid benzenoid hydrocarbons, thioarenoids, and [N]phenylenes. It is pointed out that the numerical Kekulé structures can be obtained for any class of polycyclic conjugated systems that possesses standard Kekulé structures. The reconstruction of standard Kekulé structures from the numerical ones is straightforward for catacondensed systems, but this is not so for pericondensed benzenoid hydrocarbons. In this latter case, one needs to use two codes to recover the geometrical Kekulé structures: the Wiswesser code for the benzenoid and the numerical code for its Kekulé structure. There is an additional problem with pericondensed benzenoid hydrocarbons; there appear numerical Kekulé structures that correspond to two (or more) geometrical Kekulé structures. However, this problem can also be resolved.