Stability studies of arsenic, selenium, antimony and tellurium species in water, urine, fish and soil extracts using HPLC/ICP-MS

The stability of arsenic, selenium, antimony and tellurium species in water and urine (NIST SRM 2670n) as well as in extracts of fish and soil certified reference materials (DORM-2 and NIST SRM 2710) has been investigated. Stability studies were carried out with As(III), As(V), arsenobetaine, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), phenylarsonic acid (PAA), Se(IV), Se(VI), selenomethionine, Sb(III), Sb(V) and Te(VI). Speciation analysis was performed by on-line coupling of anion exchange high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS). Best storage of aqueous mixtures of the examined species was achieved at 3 degrees C whereas at -20 degrees C species transformation especially of selenomethionine and Sb(V) took place and a new selenium species appeared within a period of 30 days. Losses and species transformations during extraction processes were investigated. Extraction of the spiked fish material with methanol/water led to partial conversion of Sb(III), Sb(V) and selenomethionine to two new antimony and one new selenium species. The other arsenic, selenium and tellurium species were almost quantitatively extracted. For soil spiked with MMA, PAA, Se(IV) and Sb(III), recoveries after extraction with water and sulfuric acid (0.01 mol/L) were below 20%.     

Isolation and purification assay of ex vivo photosystem II D1 protein toward integrated biointeraction analysis

Protein extracts of photosystem II were prepared from leaf chloroplasts of different plant species by fast and nondenaturing methods. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blot analysis of the proteins obtained showed that the extracts were enriched by D1 proteins, which appeared putatively in association with the 33-kDa oxygen-evolving-complex subunits. In further isolation steps D1 proteins were purified using salt-gradient chromatography (fast protein liquid chromatography) and characterized by western blot and mass spectrometry.     

Double induction asymétrique: hydroxyalkylation diastéréosélective de la l-alanine par le L-glycéraldéhyde

Synthesis of branched chain sugar derivative: Use of double asymmetric induction to enhance diastereoselection in hydroxyalkylation of L-alanine by glyceraldehyde.     

A model for current oscillations in the Si-HF system based on a quantitative analysis of current transients

The physical character of local oscillators on a nm scale will be outlined. Next-neighbor coupling leads to percolation areas of about 100 nm as result of Monte Carlo simulations. The percolation provides an intrinsic synchronization mechanism leading to macroscopic oscillations. Received: 24 September 1997/Accepted: 22 April 1998     

Quasiclassical Born–Oppenheimer Approximations

We discuss several problems in quasiclassical physics for which approximate solutions were recently obtained by a new method, and which can also be solved by novel versions of the Born–Oppenheimer approximation. These cases include the so-called bouncing ball modes, low angular momentum states in perturbed circular billiards, resonant states in perturbed rectangular billiards, and whispering gallery modes. Some rare, special eigenstates, concentrated close to the edge or along a diagonal of a nearly rectangular billiard are found. This kind of state has apparently previously escaped notice.     

A simple model for a two-stage chemical reaction with diffusion

We analyse the evolution of a two-stage chemical reaction betweentwo neighbouring plumes of reactants. Under the assumption thatthe plumes are approximately Gaussian we derive a system ofordinary differential equations for the total amount, the centroidand the variance of each reactant. We compare the solution ofthese equations with full numerical simulation of the reaction.Excellent agreement is obtained, with solution of the near-Gaussianmodel requiring considerably less computational effort thanthe full simulations. Of key importance is the yield of thereaction, and we discuss this feature in particular.     

Analytische Anwendungen der Differenzspektroskopie am Beispiel der Fluorid- und simultanen Molybd?n/Wolfram-Bestimmung

Zusammenfassung Zur quantitativen photometrischen Elementbestimmung wird die Methode der Differenzspektroskopie vorgeschlagen, da sie sich gegenüber herkömmlichen Verfahren durch größere Empfindlichkeit, verringertes Geräterauschen und verbesserte Nachweisgrenze auszeichnet. Die sonst störende Absorption des freien Liganden tritt nicht in Erscheinung, so daß auch bei dicht nebeneinanderliegenden Extinktionsmaxima von Komplex und Ligand die Konzentration des Komplexes exakt bestimmt werden kann. Neben einer generellen Verbesserung bisheriger Methoden lassen sich neue empfindlichere Liganden für Konzentrationsbestimmungen und zusätzlich Simultanbestimmungen zweier Elemente erschließen. Die Verbesserung der Nachweisempfindlichkeit wird am Beispiel der Fluoridbestimmung mit Cer-Alizerinkomplexonat demonstriert, die Ermöglichung neuer Analysenverfahren am Beispiel der simultanen W/Mo-,W/V- und V/Sn-Bestimmung mit Pyrogallolrot.Herrn Prof. Dr. E. Blasius zum 60. Geburtstag gewidmet