Automation of the gas analysis of14C-labelled compounds utilizing a piston-type counter tube

In this paper an automatic apparatus designed for the radioactivity measurement of¹⁴C-labelled organic compounds in the gaseous phase is described. The labelled organic compounds are combusted in a mixture of argon and oxygen. After combustion the oxygen content of the gas is eliminated by passing it through a copper packing. The water and heteroelements present are also removed and the radioactive carbon dioxide gas is swept by argon carrier gas into a piston-type counter tube. In the counter tube the piston forming a dividing wall moves forward in accordance with the rate of combustion and sweeping, and thus sucks the gases leaving the combustion tube into the effective tube volume. The anode wire is carried by a reel located in the piston and a spring device ensures its stretched state. At the end of the sweeping period methane is fed into the counter tube and the activity of the argon—methane—carbon dioxide mixture is measured in the limited proportional region. Manual and automatic operation is possible. The piston-type counter tube provides possibility for strandardization by means of extrapolation and for measurement of absolute activities.     

Determination of Rb and Sr concentrations in rocks by radioisotope X-ray fluorescence analysis

A method is described for Rb and Sr concentration determinations in rocks by radioisotope X-ray fluorescence analysis. The yield/concentration ratios were established by increasing the concentrations of the examined elements in the sample and recording each spectrum. The analytical error in the 100-1,000 ppm concentration range was 2–4%, and for 50 ppm about 10%, and the detection limit was 5–10 ppm.     

Thermal studies of pre-formulates of metronidazole obtained by spray drying technique

Compatibility studies between active drugs and excipients are substantial in the pharmaceutical technology. The objective of the present work was to develop pre-formulated mixtures of metronidazole (MT) obtained by spray drying (SPDR) and their thermoanalytical characterization. Dynamic and isothermal TG, conventional DSC and DSC coupled to a photovisual system were used. DSC experiments with both techniques confirmed the homogeneity of the conventional and pre-formulated mixtures. The TG data made possible the comparison the thermal stability of the different mixtures. Similar thermal stabilities were found of the conventional and pre-formulated mixtures, with slower particles sizes of MT.     

Pt- (and Co-) Promoted Molybdena-Alumina Catalysts: Analysis of the Impregnation Steps

The equilibrium parameters for the adsorption of Mo(VI) on gamma-Al(2)O(3) and of Co(II) and Pt(IV) on MoO(3)/gamma-Al(2)O(3) were determined. The adsorption isotherms were performed from aqueous solutions of the corresponding precursors on two different alumina supports. According to the classification given by Giles, L-type-shaped, subgroup 2, adsorption curves were found for the system Mo on gamma-Al(2)O(3), L-type, subgroup 1, for the Pt on MoO(3)/gamma-Al(2)O(3), and S-type for Co on the MoO(3)/gamma-Al(2)O(3) system. Numerical calculations were carried out for all the isotherms to find the equilibrium parameters. These constants are being used to model the development of Pt, Co, and Mo profiles on MoO(3)/gamma-Al(2)O(3) or gamma-Al(2)O(3) extrudates, respectively, which belong to the new generation of noble-metal-MoO(3)/gamma-Al(2)O(3)-supported catalysts to be used in oil-refining processes. Copyright 2001 Academic Press.     

Reduction requirements for Ru/(K)Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> catalytic activity in water-gas shift reaction

This paper is focused upon the influence of potassium on the reduction behavior and catalytic properties of Fe₂O₃, Ru/Fe₂O₃ and Ru/(K)Fe₂O₃ catalysts for the water gas shift (WGS) reaction. The effect of promotion by potassium is attributed to stabilization of a highly dispersed ruthenium phase on the iron oxide surface. The hydrogen reduction behavior of Fe₂O₃ catalysts is strongly influenced by time-pressure dependent processes and comprises two or three heavily overlapped TPR peaks which can be ascribed to the following stages of the iron(III) oxide reduction 3Fe₂O₃ 2Fe₃O₄ 6FeO 6Fe. The appearance of FeO as an intermediate phase was confirmed by XRD. The presence of ruthenium(IV) oxide substantially changes the kinetics of the reduction process. In the case of potassium-doped catalysts, the reduction of Fe₂O₃ is substantially different and is assigned to the reduction phase of KFeO₂. Both ruthenium and potassium have a promoting effect on the catalytic activity for the WGS reaction.From Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 930–941.Original English Text Copyright © 2004 by Jówiak, Maniecki, Basiska, Góralski, Fiedorow.This article was submitted by the authors in English.     

Characterization and TLC-Bioautographic Detection of Essential Oils from Some Thymus Taxa. Determination of the Activity of the Oils and their Components Against Plant Pathogenic Bacteria

JPC – Journal of Planar Chromatography – Modern TLC - The chemical composition of the oils of four thyme (Lamiaceae) chemotypes (Thymus vulgaris L., Thymus serpyllum L., Thymus x...     

On the High Viscosity of Aqueous Solution of Lysozyme Induced by Some Organic Solvents

A remarkably high viscosity has been induced in protein aqueous solutions by the addition of certain structurally related organic solvents. The effect has been observed for lysozyme aqueous solutions containing tetramethylurea (TMU), dimethylsulfoxide (DMSO), dimethylformamide, and hexamethylphosphortriamide. The effect has also been induced in ferrocytochrome c aqueous solutions by TMU. Critical concentrations for both the protein and organic solvent were verified for the onset of the viscosity increase. A common feature of the solvents which were able to induce the effect is a dipolar moiety (C=O, S → O and P → O) and a nonpolar region represented by the methyl groups. The resulting fluids show an extremely restricted flow and a typical non-Newtonian, pseudoplastic behavior. Use was made of¹H nuclear magnetic resonance (NMR) and Raman spectroscopy to characterize protein structural modifications and of¹³C NMR to investigate changes in relaxation times and chemical shifts in the solvent/water solutions. A systematic rheological characterization of the systems was undertaken for some of the solvents, and unusual patterns of viscous effects were identified for the solvent/water systems both with and without protein. The process was found to be at least partially reversible, as concluded from the recovered original solution rheological characteristics and the original protein¹H NMR spectrum, after eliminating the organic solvent by ultrafiltration. The whole process was characterized as consisting of two mutually independent stages. The first involves an extensive conformational transition of the polypeptide backbone, from a predominantly α-helical to increased random coiled and β-sheet structures, with the occurrence of nonorthodox protein secondary structures at regions above the solvent critical point. The second stage consists of short-lived interchain contacts leading to an entanglement of the macromolecular system as a whole. A microphase reversion in the organic solvent/water mixture, supported by¹³C NMR and rheological results, is proposed as the driving force causing the observed behavior.     

Thermal behaviour of xanthinium salts of Zn(II), Cd(II) and Hg(II)

Salts [XanH⁺]₂[MCl ₄ ^2- ] (where XanH⁺=protonated form of xanthine and M=Zn(II), Cd(II) and Hg(II) have been synthesized and studied by IR,¹H-NMR, TG and DSC. The metal is not coordinated to the ligand and forms a salt-like structure. The cationic proton is on N(7). Thermal decomposition of these salts occurs in two steps: (i) dehalogenation and (ii) decomposition. Dehalogenation enthalpies have been calculated from DSC curves.

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Zusammenfassung (XanH⁺)₂(MCl ₄ ^2- )-Salze (worin XanH⁺ die protonisierte Form von Xanthin bedeutet und M=Zn(II), Cd(II) oder Hg(II) ist) wurden synthetisiert und mit IR,¹H-NMR, TG und DSC untersucht. In diesem Fall liegt keine Koordination des Metalls mit dem Liganden vor, und es bildet sich eine salzartige Struktur aus. Das kationische Proton ist an N(7) lokalisiert. Die thermische Zersetzung dieser Salze erfolgt in zwei Schritten: (i) Dehalogenisierung und (ii) Zersetzung. Dehalogenierungsenthalpien wurden aus DSC-Kurven berechnet.

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- -, [XanH⁺]₂[MCl ₄ ^2– ], XanH⁺ — , M — , . , . . : . - .

     

Use of the Second Derivative of TG Curves for Investigation of the Exchanged Interlayer Cation in Montmorillonite

Various cation-exchanged montmorillonites (Li+, Na+, Ba2+, Mg2+, Ca2+, Mn2+, Co2+, Cu2+, Ag+, Cd2+, Hg2+, Al3+, Pb2+ and NH4+) were prepared from calcium montmorillonite and their properties were studied by means of X-ray diffraction and thermal analysis. The two methods give information on the cation exchange in the interlayer space only. X-ray diffraction studies at room temperature are mainly suitable for estimation of the exchange of cations of different valencies. At 500°C, when the structure is completely collapsed, the d value of montmorillonite depends on the non-hydrated ionic radius of the interlayer cation, but the measurement interval is limited for fine interpretation. The thermoanalytical method is suitable for a better distinction of different exchangeable cations of higher hydration energy on the basis of the DTG or DDTG curve. This revised version was published online in July 2006 with corrections to the Cover Date.