Ethyl acetate for the desorption of a liquid chromatographic precolumn on-line into a gas chromatograph

The feasibility of using ethyl acetate for the desorption of trace pollutants from a liquid chromatographic precolumn on-line into a diphenyltetramethyldisilazane-deactivated retention gap and, subsequently analysis by means of capillary gas chromatography has been demonstrated. First 5% of methanol are added to the water sample to prevent sorption of analytes onto parts of the preconcentration system. About 1 ml of this aqueous sample is injected onto a precolumn containing a polymeric stationary phase, using water–methanol (95:5, v/v) for transport and clean-up. The precolumn is desorbed with ethyl acetate and a fraction of 75 μl is injected on-line into the retention gap; separation is then achieved on a capillary CP Sil 19 column. No breakthrough of the test compounds was observed in the preconcentration step. The recovery was quantitative and the response obtained with flame ionization detection was linear in the range 0.1–100 ng/ml. The effect of varying the sorption flow rate on the recovery was studied. The system was applied to the analysis of river water.     

Spezielle nichtkommutative pappussche affine zweiseitige Inzidenzgruppen

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Die Züchtung von KCl-Einkristallen mit bekanntem Tl-Gehalt und die Bestimmung des Verteilungskoeffizienten

A modifiedCzochralski method for the growth of single crystals is described. This technique permits controlled doping of the crystal with easily volatile additives. The impurity distribution within the crystal is calculated. Analysis of crystal and remaining melt permits determination of the distribution coefficient. — Pure single crystals of KCl quite homogeneously doped with Tl in a range of molar concentration from 4.10^?8?1.10^?4 were grown by this method. Their Tl content was determined radiochemically to within 3%. The distribution coefficient was found to bek=0.31±10% throughout the range of concentration under investigation. It is shown that the effect of evaporation may not be neglected.     

Extinction of Radiation in Sterically Interacting Systems of Monodisperse Spheres. Part 2: Experimental results

The Bouguer-Lambert-Beer law (BLBL), commonly used to describe the extinction of radiation in disperse systems, is known to be valid in the limit of low concentrations only. In Part [1] it was shown that steric particle-particle interactions lead to important effects in the range of high particle concentration and two versions of a more general extinction equation including steric interactions were derived for the regimes of fraunhofer diffraction and ray propagation in this part experimental evidence for the effects of steric interactions on the extinction of radiation in suspensions of monodisperse spherical particles is given. Various experiments on light extinction and on ultrasonic extinction are combined to cover a broad range of particle size parameters, mechanisms of particle-wave interaction and receiver apertures.     

Produkte endlicher einfacher Gruppen

Ohne Zusammenfassung