Versuche zur Anreicherung von Spurenelementen durch Ausf?llen des Hauptbestandteils

Zusammenfassung Selenitionen werden aus schwach sauren Lösungen selektiv von Bleisulfat mitgefällt. Das Selenit wird dabei wahrscheinlich an die durch überschüssige Pb²⁺-Ionen positiv geladenen Bleisulfat-Partikel gebunden. Aus neutralen Probelösungen fällt daneben auch Bleiselenit zusammen mit PbSO₄ aus. Man kann so kleinste Selenmengen durch Zusatz einer Bleisulfat-Suspension aus Probelösungen verschiedenartiger Zusammensetzung anreichern, wobei die Ausbeuten in den meisten Fällen für eine quantitative Bestimmung hinreichend hoch sind. Das angereicherte Selen wird nach Lösen des PbSO₄-Trägers in Ammoniumtartratlösung photometrisch mit 3,3-Diaminobenzidin bestimmt. Die meisten Schwermetallionen sowie viele Anionen stören die Se-Anreicherung auch in 10⁴-bis 10⁶fachem Überschuß nicht. Analysen von metallischem Blei und Kupfer mit wenigen ppm Selen sind mit relativen Standardabweichungen von etwa 0,05 durchführbar.

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Summary Selenite is selectively co-precipitated with lead sulphate. In weakly acid solutions the selenite ions are attached to the lead sulphate particles probably the PbSO₄ being charged electrically by adsorbed Pb²⁺-ions in excess. Moreover, in neutral solutions selenite will co-precipitate with PbSO₄ as lead selenite.Using a suspension of lead sulphate small amounts of selenium may be enriched in samples of very different materials. In most cases the effect of enrichment will be sufficient for analytical purposes. The selenium is determined photometrically using 3,3-diaminobenzidine as reagent after the PbSO₄-collector is solved in ammonium tartrate solution. Most ions of heavy metals and many anions do not interfere with the process even in an excess of 10⁴ to 10⁶ fold.Thus it is possible to determine a few ppm of selenium in metallic samples of lead and copper. The relative standard deviation is found to be about 0.05.

     

Identification of dimethyl- and ethylphenanthrenes in HPLC-fractions of rock and coal extracts by capillary gas chromatography and high resolution spectrofluorometry at 15K

Summary Total-aromatics fractions from an oil shale and a coal extract were fractionated in a three-step HPLC procedure. C₂-phenanthrenes in the triaromatic subfraction from the first step were tentatively identified on the basis of retention indices and GC-MS data. Successive fractionation of triaromatics on reverse-phase columns yielded 20 subfractions that were amenable to a positive identification of individual C₂-phenanthrene isomers by using high resolution spectrofluorometry. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Spherical complexes and nonprojective toric varieties

A combinatorial criterion for a toric variety to be projective is given which uses Gale-transforms. Furthermore, classes of nonprojective toric varieties are constructed.     

Evaluation of a diffusive sampling method for the determination of atmospheric ammonia

A diffusive sampling method is presented for the determination of atmospheric levels of ammonia based on the collection of ammonia at the phosphoric acid coated bottom of small glass vials and subsequent flow injection analysis of the trapped ammonium. In order to avoid effects of varying wind velocities on the sampling rate, the tube-type samplers are covered with a hydrophobic microporous membrane. The experimentally obtained uptake rate of the diffusive samplers (i.e. 7.8 ml min^–1) is in excellent agreement with the theory. The analytical characteristics of the method with respect to sensitivity, selectivity, dynamic range, precision and practicability are evaluated in detail. As the detectability of the proposed method is related to both the mass collected during exposure and the mass sensitivity of the detection step, the role of microanalytical procedures in general, and significance of meticulous control of contamination in particular are discussed. Under optimum conditions the gas-phase detection limit achievable (in terms of time independent exposure dose value) is about 2.3×10³ g m^–3 s^–1, which permits measurements at low g m^–3-levels with a time resolution of a few hours. Application of the method to indoor and outdoor measurements proved its suitability for routine purposes.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Center-of-mass deflections in two processes: Collision-induced dissociations of 10 keV H 2 + ions in their electronic ground state 1sσ g and dissociative electron capture

By means of a flight-time difference apparatus the two collision induced processes of dissociative vibrational excitations $$H_2^ + (10keV,1s\sigma _g ) + target \to (H_2^ + )*(1s\sigma _g ) \to H^ + + H(1s)$$ and $$H_2^ + (10keV,1s\sigma _g ) + target \to (H_2 )*(unspecified) \to H + H$$ have been determined from an asymmetry in the lab-frame resulting from deflections of the centers-of-mass of the incident projectiles. H⁺+H velocity distributions from vibrational excitations of the electronic ground state of the H ₂ ⁺ ions will be presented which have been directly measured. Competition of any of the higher lying electronically excited states of the projectiles is estimated to be negligible. In the case of dissociative electron capture combined with simultaneous deflections of the centers-of-mass the electronic states of the intermediate H₂ molecules and of the H fragments could not be specified.     

Gas chromatographic determination of trace amounts of vinyl chloride and dichloroethenes in landfill-gas

A method for the determination of vinyl chloride (VC) and dichloroethenes (DCE) in gas samples is presented. The analytes are preconcentrated from a gas-volume of up to 20 l on an adsorption tube filled with 1.0 g of a carbon molecular sieve at a flow rate of 80 l/h and are subsequently desorbed with carbon disulfide. Vinyl bromide is added as internal standard to the extract. The analytes are determined as their 1,2-dibromo-derivatives by capillary gas chromatography with electron capture detection. The detection limits have been found to be 82 ng/m(3) = 32 ppt (VC), 190 ng/m(3) = 48 ppt (1,1-DCE) and 96 ng/m(3) = 24 ppt (cis-/trans-1,2-DCE). The method has been used for the quantification of the anaerobic microbial degradation of tetra- (PCE) and trichloroethene (TCE) to dichloroethenes and vinyl chloride in landfill sites. The substances have been analyzed in landfill-gas as well as in gaseous emissions from the landfill surface. The mean emission rates of tetrachloroethene, trichloroethene and vinyl chloride from the landfill surface into the ambient air are about 0.5 microg/(m(2) x h).     

DFT‐EPR study of radiation‐induced radicals in α‐D‐glucose

The structures of two radiation‐induced radicals in solid‐state α‐D ‐glucose have been identified by means of single‐molecule density function theory (DFT) calculations. Using the original crystalline structure as input, several radical models were created and their geometries optimized. Subsequently, electron paramagnetic resonance (EPR) parameters were calculated. During these calculations, the global orientation of the radical structure was kept fixed with respect to the crystal axes reference frame. This was essential to allow for an easy analysis of the hyperfine tensor principal directions, besides the isotropic and anisotropic coupling constants. By comparing these calculated EPR parameters with their experimentally determined counterparts, a plausible identification of two carbon‐centered glucose radicals was possible. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004