Aktivierungsanalytische Untersuchungen an hochreinem Silicium

Zusammenfassung Zur Aktivierungsanalyse von hochreinem Silicium wurden die vermuteten Verunreinigungen in 3 Gruppen entsprechend der Halbwertszeit ihrer zur Bestimmung herangezogenen Radionuklide zusammengefaßt und für diese Gruppen chemisch-analytische Trennungsgänge ausgearbeitet. Damit war es möglich, in relativ geringen Probemengen etwa 30 Elemente zu bestimmen. Die dargelegten Ergebnisse liegen durchweg im oder unter dem ppb-Bereich (=10^–7 %).Zur Lokalisierung einiger Verunreinigungen wird die Autoradiographie herangezogen. Einige Aufnahmen zeigen, daß dieses Verfahren auch bei Vorhegen äußerst geringer Aktivitäten noch wertvolle Aussagen zu liefern vermag.

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Summary For the activation analysis of high-purity silicon the supposed impurities are divided into 3 groups corresponding to the half-lives of the radionuclides belonging to the impurities. For these groups chemoanalytical separation schemes are developed. With this technique it was possible to determine about 30 elements in small samples. The results given are in or below the ppb-level.For localisation of the impurities autoradiography is used. Some of the pictures taken show, that also with very low activities valuable results can be obtained.

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Zum Schlu mu die freundliche Hilfe erwähnt werden, die wir an den deutschen Reaktorstationen bei der Durchuürung der Bestrahlung rehalten haben. So sind wir der Reaktorstation Garching, insbesondere den Harren Dr. Köhler und Rau zu auerordentlichem Dank für die stats gewährte Unterstüzung bei der Bestrahlung der großen Zahl der Proben verpflichtet. — Die Analyse der kurzlebigen Radionuklide verlangte das Arbeiten direkt am Reaktor. Dank dem freundlichen Entgegenkommen der Herren Prof. Dr. E. Fischer und Dr. Röbert konnten wir dieses in einem Laboratorium der Reaktorstation Geesthacht durchführen, wobei wir auch den Herren Braun und Hauser für ihre bereitwillige Unterstützung zu danken haben.Schließlich sei Herrn Dr. Brandt für die Entwicklung der erwähnten Formel auch an dieser Stelle nochmals gedankt.

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In gekürzter Form anläßlich der Tagung der Fachgruppe: Kern-, Radio- und Strahlenchemie der Gesellschaft Deutscher Chemiker in Heidelberg am 10. 9. 1963 vorgetragen.     

Extraction of macro- and microamounts of lanthanides by D2EHPA

The effect of macroconcentration (Ma) lanthanide extraction on the microcomponent (Mi) extraction by D2EHPA was investigated. The investigation corroborated that the macrocomponent suppresses the microcomponent extraction. The extractability of Mi decreases with increasing Ma concentration and with increasing proton lanthanide number in macroconcentrations. Semi-empirical relations were derived describing lanthanide extraction in lanthanide macro- and microconcentrations as a function of the extraction of lanthanide macroconcentrations. Under the conditions discussed, these relations can be used to estimate for any lanthanide the distribution ratios for the lanthanide applied as a macrocomponent and for Eu applied as a microcomponent.     

Kinetic determination of tellurium based on its inhibitory effect on the palladium(II)-catalysed reaction between pyronine G and hypophosphite ion

A kinetic method for the determination of Te based on its inhibitory effect on the PdII-catalysed reaction between pyronine G and H2PO2- is described. The influence of experimental variables on the rate of the process and the potential interfering effect of a large number of ions has been studied. Under the selected experimental conditions: 6 x 10(-5) M pyronine G; 0.6 M H2PO2-; pH 2.6, adjusted with Britton-Robinson buffer; 0.80 microgram ml-1 of PdII; and a temperature of 22 +/- 0.2 degrees C, Te was determined in the concentration range 0.08-0.85 microgram ml-1. The method was applied to the determination of Te in waters and lead concentrates.     

Gas chromatographic determination of pesticides in vegetable samples by sequential positive and negative chemical ionization and tandem mass spectrometric fragmentation using an ion trap analyser

A selective and sensitive chromatographic method is described for the determination of nine organochlorine and organophosphorus pesticides in vegetable samples by gas chromatography-mass spectrometry. The proposed method combines the use of positive and negative chemical ionisation and tandem mass spectrometric fragmentation, resulting in a significant increase in selectivity and allowing the simultaneous confirmation and quantification of trace levels of pesticides in complex vegetable matrices. Parameters relative to ionisation and fragmentation processes were optimised to obtain maximum sensitivity. Repeatability and reproducibility studies yielded relative standard deviations lower than 25% in all cases. Identification criteria, such as retention time and relative abundance of characteristic product ions, were also evaluated in order to guarantee the correct identification of the target compounds. The method was applied to real vegetable samples to demonstrate its use in routine analysis.     

Density functional study of infinite polyserine chains

Two different helical conformations (alpha and 3-10 helices) of polyserine are studied using density functional theory. The infinite system characterized by exact translational-rotational symmetry is examined in vacuum using the BLYP exchange-correlation functional. Geometry analysis in terms of hydrogen bond strength and total energies of the different conformers are presented. The structural changes due to the presence of the serine side chain are identified comparing the polyserine and polyglycine chains. The rotational energy curves of the side chain are presented for both investigated helices. Band structures of polyserine and polyglycine conformers are also compared.     

Determination of triclosan in foodstuffs

A reverse-phase high-performance liquid chromatographic (RP-HPLC) method coupled with an ultraviolet detector was developed to determine triclosan which had migrated into foodstuffs from packaging materials. The method includes extraction with hexane, followed by evaporation to dryness and residue re-dissolution in ACN 90%. Chromatographic separation was performed with a Kromasil 100 C18 column (15 cm x 0.4 cm ID, 5 microm particle size) at 30 degrees C and using ACN and water as mobile phases. Regarding recoveries, good results (higher than 83% and lower than 112%) were obtained for the three representative food matrixes selected (orange juice, chicken breast meat, and Gouda cheese).     

Experimental and quantum chemical studies of structure and reaction mechanisms of dioxouranium(VI) complexes in solution

This perspective article describes the combination of experimental data and quantum chemical methods for the determination of structure and reaction mechanisms of uranyl(vi) complexes in aqueous solution. The first part assesses the accuracy of the chemical and thermodynamic properties of solvated uranyl(vi) complexes as obtained by various quantum chemical methods. The second part discusses structure determination, mechanisms for ligand exchange and the lability of coordinated water molecules for various uranyl(vi) complexes using a combination of NMR and quantum chemical data.     

Some basic electrochemistry and the cold nuclear fusion of deuterium

The role of electrochemistry in the discovery and interpretation of the alleged cold nuclear fusion is discussed.