The silver-oxygen system in catalysis: new insights by near ambient pressure X-ray photoelectron spectroscopy

We addressed the interaction of oxygen with silver by synchrotron based near ambient pressure X-ray photoelectron spectroscopy at temperatures relevant for industrial oxidation reactions performed with silver catalysts. For silver single crystals, polycrystalline foils and powders in equilibrium with gas phase O(2), we observed the dynamics of the formation of five different atomic oxygen species with relative abundances depending on the temperature and time. Correlation of their formation kinetics with spectroscopic features and thermal stability indicates that these are distinct species with different electronic structures, which might relate to the different roles of silver in oxidation reactions.     

Die quantitative chemische Bestimmung von Vitamin D

Zusammenfassung Es werden die Bedingungen zur photometrischen Bestimmung von Vitamin D mit Antimontrichlorid und Guajakol festgelegt. Die von der Vitamin D-Konzentration abhängige, beständige Grünfärbung wird durch Sterine nicht gestört, es sei denn, daß sie in 100fachem Überschuß vorhanden sind. Fette und deren Spaltprodukte stören durch eine gelbbraune Färbung, wodurch eine Verseifung natürlicher Fette notwendig wird.Die Absorptionskurven von Vitamin D₂ und D₃ zeigen völlige Übereinstimmung. Der Vitamin D₂-Gehalt wird unter dem Einfluß von Licht und Luft vermindert, wobei sich der Luftsauerstoff ungünstiger auswirkt als Licht. Kurzzeitiges Erhitzen auf 80–100° C schädigt das Vitamin D₂ nicht, eine längere Einwirkung höherer Temperaturen bedingt einen Abfall, der in einer Stickstoff-Atmosphäre geringer ist als unter SauerstoffAtmosphäre.Durch U.V.-Bestrahlung wird das Vitamin D₂ ebenso wie durch Sonnenlicht geschädigt, wobei die Verminderung durch 3stündige Sonnenbestrahlung etwa derjenigen einer 3 Minuten langen U.V.-Bestrahlung entspricht. Der Einfluß von Suprasterin und Toxisterin auf die Vitamin D-Reaktion ist nur gering, was für die Vitamin D-Bestimmung in bestrahlten Hefen von Bedeutung ist.     

A dot-blot test using gold colloid cluster technology as a miniaturizable alternative to ELISA and hapten inhibition tests

A novel miniaturizable method to quantify antigens is described in form of a cluster linked immunosorbent assay (CLISA), using inexpensive nitrocellulose (NC) membranes as a support for dot-blotting the antigens. Antibodies for detection are labeled with gold-colloid clusters (GCC). After blocking of the membrane with non reacting protein and application of the GCC-labeled antibodies the signal is detectable by visual colorimetry and can be compared to a color scale prepared from a dilution series of known sample concentrations. The color reaction product is stable for a very long time and does not fade. The sensitivity of the method is comparable to that of ELISA if not better and furthermore needs only small amounts of antibody for detection or for GCC-labeling. This method is an alternative to the use of expensive enzyme-conjugated antibodies for a number of applications, such as tracking of antibodies during purification or hapten inhibition tests. Correspondence: Haifa Al-Dubai, Max F. Perutz Laboratories, Department of Biochemistry, University of Vienna, 1030 Vienna, Austria.     

Auswertung eines Ringversuches im Spurenbereich

Summary The evaluation of an interlaboratory comparison in trace analysis has to take account of the log-normal distribution of the results. This distribution leads to the geometric mean as a measure for the content of the investigated sample, and to a relative error for the confidence interval for the reproducibility and the repeatibility. The log-normal distribution allows to pool together the relative standard deviations from the different components of the sample. In this way the confidence interval gets narrower and the criteria for reproducibility and repeatibility can be improved, even when there was an insufficient number of laboratories taking part in the interlaboratory comparison.