Ionen-chromatographische Spurenanalyse amperometrisch detektierbarer Anionen in W?ssern

Zusammenfassung Nach einer Ionenpaar-Reversed-Phase-HPLC an einer Nitrilophase (Nucleosil 10-CN) mit Cetyltri-methylammoniumchlorid als Ionenpaarbildner werden an einer glassy-carbon-Elektrode Bromid, Iodid, Nitrit und Thiocyanat amperometrisch im Bereich von 1 bis 500 ppb detektierbar. Das Trennsystem wurde mit Methanol bzw. Acetonitril als Modifier, die Detektion durch unterschiedliche Abscheidungspotentiale zwischen +1,0 und +1,7 V variiert. Iodid- und Thiocyanat-Spuren lassen sich durch Extraktion des Ionenpaares in Chloroform vor der ionenchromatographischen Analyse aus Wässern anreichern und somit bis in den Bereich unter 1 ppb bestimmen. Für Nitrit, Bromid und Iodid werden auch die Ergebnisse von Methodenvergleichen mittels photometrischer Continuous-flow-Analyse bzw. massenspektrometrischer Isotopenverdünnungsanalyse in Trinkwässern vorgestellt.

---

Ion-chromatographic trace analysis of amperometrically detectable anions in water

Summary After an ion-pair reversed-phase hplc with cetyltrimethylammonium-chloride as ion-pair reagent, bromide, iodide, nitrite and thiocyanate are detectable at a glassy carbon electrode in a scope from 1 to 500 ppb. The separation system was varied by methanol resp. acetonitrile as modifier, the detection system by different deposition potentials between +1.0 and +1.7V. Iodide and thiocyanate traces are enrichable from waters by extraction of ion-pairs in chloroform before ion-chromatographic analysis and are detectable below 1 ppb. For nitrite, bromide and iodide the results of a comparison of methods by photometric continuous-flow-analysis and isotope dilution mass spectrometry in drinking waters are presented.

---

---

Die Arbeit wurde im Rahmen des DFG-Schwerpunktprogramms 'Hydrogeochemische Vorgänge im Wasserkreislauf in der ungesättigten und gesättigten Zone gefördert.Wir danken Herrn Prof. K. Heumann, Regensburg für die gute Zusammenarbeit im Rahmen der Vergleichsanalysen.     

Species analysis of elements in foods

In environmental analysis the determination of the individual concentrations of the various chemical forms of an element is becoming increasingly important. Bioavailability and toxicity depend on these element species, and analytical methods and strategies for species analysis in foods are now being devised.     

Darstellung von 2,2,3,3,5,5,6,6-octamethyl-1,4-dithiacyclohexasilan, 2,2,3,3,5,5,6,6-octamethyl-1,4-diselenacyclohexasilan und 2,2,3,3,5,5,6,6-octamethyl-1-selena-4-thiacyclohexasilan

Octamethylcyclotetrasilane reacts with elemental sulfur or selenium in toluene at 220°C to give the six-membered heterocycles [(Me₂Si)₂S]₂, [(Me₂Si)₂Se]₂ and Me₂ iMe₂.     

Homoatomic Bonding of Main Group Elements

Clusters of main group elements are not rare. On the contrary, it is becoming difficult to avoid the discovery of new substances of this type. Clusters are the natural intermediate stages between an element and its isolated atoms or ions. In the form of polycations and polyanions they offer models for the stepwise oxidation and reduction of an element and represent a bridge between the elements. The great majority of homonuclear bonded structures are already present in the solid phases of simple systems. Mobilization of these clusters as molecules represents a great challenge.     

Maximizing a lower bound on the computational complexity

We solve a combinatorial problem that arises in determining by a method due to Engeler lower bounds for the computational complexity of algorithmic problems. Denote by G_d the class of permutation groups G of degree d that are iterated wreath products of symmetric groups, i.e. G = S_dh?11?1S_d0 with Π^h?1_i=0d_i = d for some natural number h and some sequence (d₀,…,d_h?1) of natural numbers greater than 1. The problem is to characterize those G = S_dh?11?1S_d0 in G_d on which k(G):=log|G|/max_0≤i≤h?1log(d_i!) assumes its maximum. Our solution consists of two necessary conditions for this, namely that d₀≤d₁≤?≤d_h and that d_h is the largest prime divisor of d. Consequently, if d is a prime power, say d = p^h with p prime, then a necessary and sufficient condition is that d_i = p, 0 ≤ i ≤ h ? 1.     

DieK-Fluoreszenzausbeute von Titan und der Zerfall des48Vanadium

TheK-fluorescence yieldΩ _K of Titanium has been measured using the coincidence method and investigating the electron capture decay of⁴⁸V. The detectors used have been a Si(Li)- and a Ge(Li)-detector for the X- andγ-rays. The experimental results areP _K Ω _K =0.2005 ±0.0030 andΩ _K (Ti)=0.224±0.003 usingP _K =0.896. For the branching ratios of the decay of⁴⁸V we obtainedEC (3.239) 7.9±0.6%EC (3.224) 2.9±0.4%EC (2.295) 35.6±2.0% Β⁺ (2.295) 52±1.0% all others 1.6%. Additionally someγ-ray-energies of the decay of⁴⁸V and the half-life,T _{1 2}=(16.23 ±0.03)d, have been measured.