Eine neue Methode zur gewichtsanalytischen Bestimmung der reduzierenden Zucker unter Anwendung der Zentrifuge

Ohne Zusammenfassung1) Vergl. Meillère und Chapelle, diese Zeitschrift41, 100.     

Die Bestimmung der Oxybutters?ure

Ohne Zusammenfassung     

Comparison of Derivatization Methods for the Determination of Butyl- and Phenyl-tin Compounds in Mussels by Gas Chromatography

Two different derivatization methods, alkylation with Grignard reagents, and ethylation with sodium tetraethylborate, were compared for the determination of organotin compounds, viz. tributyltin, dibutyltin, monobutyltin, triphenyltin, diphenyltin and monophenyltin, in mussel samples. Temperature, reaction time and concentration of Grignard reagents were optimized in the former method; in the latter the effect of pH, concentration of sodium tetraethylborate and reaction time were studied. In the derivatization with Grignard reagents hexyl, pentyl, propyl, ethyl and methyl were used as alkyl Grignard groups. A critical evaluation of the different derivatization methods is presented. © 1997 John Wiley & Sons, Ltd.     

Laser-Induced fluorescence detection in conventional-size liquid chromatography with a frequency-doubled argon-ion laser

Laser-induced fluorescence (LIF) detection in conventional-size column liquid chromatography is achieved at 257 nm with a frequency-doubled argon-ion laser. Short-wavelength excitation offers two important advantages: firstly, a wide variety of analytes can be excited, and secondly, the Raman scatter of the eluent does not interfere with the fluorescence of the analytes. A standard mixture of polynuclear aromatic hydrocarbons was studied, both with LIF detection and with a commercially available sensitive conventional fluorescence detector. The improvement in the detection limits ranges from about a factory of 4 to 30; the LIF detection limits are typically at the 50 ng l^?1 level, which corresponds to an injected amount of 0.5 pg.     

Synthesis and characterization of electrical conducting porous carbon structures based on resorcinol–formaldehyde

Electrical conducting carbon (ECC) porous structures were explored by changing the pyrolysis temperature of organic xerogel compounds prepared by sol–gel method from resorcinol–formaldehyde (RF) mixtures in acetone using picric acid as catalyst. The effect of this preparation parameter on the structural and electrical properties of the obtained ECCs was studied. The analysis of the obtained results revealed that the polymeric insulating xerogel phase was transformed progressively with pyrolysis temperature into carbon conducting phase; this means the formation of long continuous conducting path for charge carriers to move inside the structure with thermal treatment and the samples exhibited tangible percolation behaviour where the percolation threshold can be determined by pyrolysis temperature. The temperature-dependent conductivity of the obtained ECC structures shows a semi-conducting behaviour and the I(V) characteristics present a negative differential resistance. The results obtained from STM micrographs revealed that the obtained ECC structures consist of porous electrical conducting carbon materials.