Austausch von Chrom(III) mit Chrom(II) und Szilard—Chalmers-Reaktion von Kaliumchromat

Zusammenfassung Durch Versuche mit⁵¹Cr wird gezeigt, daß Cr³⁺ mit Cr²⁺ austauscht, wenn man ein Chrom(III)-Salz in wässeriger Cr²⁺-Lösung auflöst, d. h. die Hydratation zum reaktionsträgen [Cr(H₂O)₆]³⁺ verläuft relativ langsam. Die Bedeutung dieses Austausches für dieSzilard—Chalmers-Reaktion von Chromat wird diskutiert.

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Experiments with⁵¹Cr prove the exchange of Cr³⁺ with Cr²⁺ when a Cr(III)-salt is dissolved in an aqueous solution of Cr²⁺. This indicates that the hydration to the inert [Cr(H₂O)₆]³⁺ is relatively slow. The importance of this exchange for theSzilard—Chalmers reaction of chromate is discussed.

     

Th,U and trace elements determination in Egyiptian Lake sediments by INAA and laser fluorimetry

A study was undertaken to determine element concentrations in Aswan High Dam Lake sediments. Sediment samples were collected from 40 to 500 km upstream of the dam to follow the sedimentation process and the distribution of Th, U and the trace elements in the lake. INAA was applied for the determination of Sm, Ce, Lu, Th, Cr, Yb, Au, Hf, Ba, Nd, Cs, Tb, Sc, Rb, Fe, Zn, Co, Eu, and Sb, while Laser Fluorimetry was applied for U determination. The accuracy and the reproducibility of the techniques were tested with IAEA standard materials (SL, Soil-7). The U values ranged from 4 ppm to 18 ppm, Th values were between 2 and 10 ppm, and showed a very good correlation with the rare earth elements and Fe. The distribution of most of the elements in the lake follows the same trend as the distribution of the clays in the sediments. Ba showed a negative correlation with most of the elements under investigation.Paper presented at the 3th International Conf. on Nuclear and Radiochemistry (NRC-3), Vienna, 1992.     

Activation analysis with a high-resolution high rate gamma-spectroscopy system

A high-resolution high-rate ψ-spectroscopy system is essential or, respectively, useful in three groups of applications: (1) measurement of nuclides with half-lives of less than one second; (2) Measurement of nuclides with half-lives in the second range at high sample activity; (3) Measurement in the same counting geometry of sample series of highly different sample activities. Examples are given for these applications.     

Isotachophoresis of beta-blockers in a capillary and on a poly(methyl methacrylate) chip

Analysis of the beta-blockers oxprenolol, atenolol, timolol, propranolol, metoprolol, and acebutolol in human urine by a combination of isotachophoresis (ITP) and zone electrophoresis (ZE) was investigated. Methods were developed with a conventional capillary electrophoresis (CE) apparatus and a poly(methyl methacrylate) (PMMA) microchip system. With CE the separation of oxprenolol, atenolol, timolol, and acebutolol from a standard solution containing 5 microg/mL of each compound was accomplished by performing ZE with transient ITP. The electrolyte system consisted of 10 mM sodium morpholinoethane sulfonate (pH 5.5) and 0.1% methylhydroxyethylcellulose as the leading electrolyte and 30 mM ortho-phosphoric acid (pH 2.0) as both the terminating and the ZE background electrolyte. With the microchip system the separation of oxprenolol and acebutolol from a standard solution containing 10 microg/mL of each compound was accomplished by a coupled-channel ITP-ZE device using the same leading electrolyte solution as the CE system but 5 mM glutamic acid (pH 3.4) as terminating and background electrolytes. The systems were used for analyses of patient urine samples. Water-soluble hydrophilic matrix compounds were removed from the urine samples by solid-phase extraction (SPE). Limits of quantification below 5 microg/mL could be achieved. The PMMA ITP-ZE chip has not earlier been used for analyses of any drugs from urine samples.     

Chelataustauscher auf Oxinbasis, 2. Mitt.: Zur Theorie der Komplexbildung im Chelataustauscher

Zusammenfassung Durch Messung der Verteilungskoeffizienten wird der Nachweis erbracht, daß Chelataustauscher durch Zusatz von Metalloxinaten, z. B. von Al- und Ba-Oxinat, während der Kondensation der Harze selektiver gemacht werden können. In dieser Arbeit werden die pH-lg _ex-kurven verschiedener Oxinatharze diskutiert. Die Form der Kurven wird aus dem Zusammenwirken von Komplexbildung, Donnan-Verteilung und Austauschvorgängen mit Carboxylgruppen abgeleitet. Die Steigungen der pH-lg _ex-kurven werden als Maß für die mittlere Ligandenzahl verwendet. Die Selektivität der Austauscher wird durch die pH₁₀₀-Werte charakterisiert. Damit wird der Nachweis erbracht, daß die sterische Anordnung des Oxins im Harz für die Selektivität mitverantwortlich ist.

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By measuring the distribution coefficients it is shown that the selectivity of chelate resins can be raised by adding metaloxinates of Al and Ba, e.g., during the condensation. The pH-lg _ex-curves of various oxinate resins are discussed in this paper. The shape of the curves is derived from the interaction between complex formation, Donnan-distribution and exchange with carboxylic groups. The slope of the pH-lg _ex-curves is used as measure for the average ligand number. The selectivity of the resins is characterized by the pH₁₀₀ (pH value at _ex=100). From these experiments it follows conclusively, that the steric arrangement of the oxine in the resin is responsible for the selectivity.

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Mit 8 Abbildungen

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1. Mitt. (s. S. 1050) wird im folgenden I genannt.     

Electrophoretic separation of carrier-free radionuclides

The electrophoretic separation of radioactive rare earths on Cellogel in α-hydroxyisobutyric acid is described. Minute amounts of radioactive daughter nuclides are separated from the neutron-irradiated rare earth target materials, the ratio of the substances being 10⁵∶1 to 10⁷∶1. The suggested method is simple, rapid and suitable for analytical purposes.     

Capital Accumulation and Embodied Technological Progress

This paper combines technology adoption with capital accumulation taking into account technological progress. We model this as a multi-stage optimal control problem and solve it using the corresponding maximum principle. The model with linear revenue can be solved analytically, while the model with market power is solved numerically. We obtain that investment jumps upwards right at the moment that a new technology is adopted. We find that, if the firm has market power, the firm cuts down on investment before a new technology is adopted. Furthermore, we find that larger firms adopt a new technology later.