Untersuchungen zum Alkalischen Abbau von kieselgelen mittels Leitfähigkeitsmessungen

Investigations of the Alkaline Degradation of Amorphous Silica by Means of Conductivity Measurements Two silicas produced in different ways are characterized by conductometric pursuit of their reaction in alkaline medium. It is tried to interpret the parameters obtained by formal kinetic analysis of the measured results according the Avrami-Erofeev-equation and to receive references to the mechanism of the reaction.     

Untersuchung von Szilard-Chalmers-Reaktionen mit hilfe der Dünnschichtchromatographie

After irradiation with neutrons, bariumkryptate nitrate was separated from barium nitrate by thin layer chromatography. The¹³⁹Ba activities in the two fractions were measured. After decay, the relative amounts of stable barium were determined by neutron activation analysis. A formula was derived for the calculation of the enrichment factor directly from the four counting rates. The two components mentioned above, one or the other with¹³¹Ba as tracer, were brought into contact with each other for a moment and then separated by chromatography. The exchange rates indicated that the enrichment had been cancelled to a large degree by isotopic exchange. The procedures, recommended as a test for Szilard-Chalmers targets, were checked out with cobalt(III) acetylacetonate.     

Sensitivities and detection limits of X-ray fluorescence analysis with a 10 mCi241Am source

Sieben Spurenelemente im Bereich von Chrom bis Barium wurden auf Amberlite IR-120 Kationenaustauschpapier angereichert und durch energiedispersive Röntgenfluorescenzanalyse mit einer 10 mCi²⁴¹Am-Quelle bestimmt. Die Übereinstimmung der experimentell gemessenen mit den theoretisch berechneten Empfindlichkeiten wird geprüft. Die Nachweisgrenzen werden verglichen mit den in typischen Oberflächengewässern vorkommenden und den in Trinkwasser maximal erlaubten Elementkonzentrationen. Die Möglichkeit der Anwendung in der Umweltanalytik wird diskutiert.

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Empfindlichkeiten und Nachweisgrenzen der Röntgenfluorescenzanalyse mit einer 10 mCi²⁴¹Am-Quelle

Summary Seven trace elements ranging from chromium to barium were preconcentrated on Amberlite IR-120 cation exchange paper and determined in an energy dispersive X-ray fluorescence system using a 10 mCi²⁴¹Am source. Sensitivities were experimentally determined and checked with theoretically calculated values. The detection limits are compared with elemental levels present in typical surface waters and those allowed in drinking water. Appropriate conclusions as to feasibility of such a system for environmental monitoring are drawn.

     

The near-best solution of a polynomial minimization problem by the Carathéodory-Fejér method

For a compact set C, 1, we consider the Chebyshev problem

Soft X-ray magneto-optics at rare-earth 4d-4f thresholds

We report on X-ray magneto-optics (XMOKE) at the 4d-4f excitation threshold of rare-earth elements and its application to measuring temperature-dependent magnetization as well as element-specific hysteresis curves in heteromagnetic multilayers. We outline some advantages of XMOKE as compared to standard magnetooptics in the visible light regime. Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001     

Quinoxalines. Part 13: Synthesis and mass spectrometric study of aryloxymethylquinoxalines and benzo[b]furylquinoxalines

A series of new aryloxymethylquinoxalines, benzo[b]- and naphtho[2,1-b]furylquinoxalines, possessing potential biological activity, was prepared, characterized by IR and NMR spectroscopy and their electron ionization (EI) mass spectra studied in detail. The aryloxymethylquinoxalines were obtained by reacting halogenomethylquinoxalines with bifunctional O-nucleophiles. The benzo[b]furylquinoxalines and naphtho[2,1-b]furylquinoxalines were prepared via two routes, which differed in the order of the two cyclization steps involved in the syntheses. The composition of the ions obtained by EI mass spectrometry were determined by accurate mass measurements and the fragmentation pathways clarified by B/E linked scans and collision induced dissociation. The mass spectrometric behaviour of the compounds studied as to the possible loss of OH radicals proved to be very characteristic.