A simple laboratory generator for low concentrations of sulphur dioxide

The generator is based on permeation of sulphur dioxide through silicone rubber tubes immersed in a buffered, thermostated solution of sodium hydrogensulphite. The generator contains three (or more) permeation tubes of different lengths immersed simultaneously in the generation solution. The tubes can be connected stepwise to the carrier gas source, so that three (or more) different concentrations of SO₂ in the carrier gas can be obtained from a single solution. The tested generator produced 1.25–25.4 ng s^?1 SO₂, depending on the hydrogensulphite concentration in the solution. Long-term stability was tested for the production of 10.49 ng s^?1 over 50 h; the relative standard deviation was 1.57%. The experimental conditions affecting the production of SO₂ are discussed. An equation is derived for estimating the SO₂ production for various solution compositions and surface areas of the permeation tubes.     

Effects of genesis and ionizing radiation on the kinetics of reduction of NiO-CeO2 mixed oxides with hydrogen

The reduction of mixed oxides NiO-CeO₂ of various composition with hydrogen was studied at 290–470° by means of thermogravimetry. Some physicochemical properties of the system were also investigated and compared with earlier studied analogous samples of different “origin”. The degree of mutual interaction of the two components, the reduction kinetics and the sensitivity to the different sorts of radiation (gamma-rays, fast neutrons and electrons), applied in different doses, are strongly affected by the “pre-history” and by the composition in both compared series of mixed oxides.     

Beitrag zur mikroskopischen Identifizierung organischer Stoffe nach L. Kofler. V

Zusammenfassung In Fortsetzung früherer Untersuchungen zum Zweck der Ergänzung und Erweiterung der Identifizierungs-Tabelle nachKofler werden für 62 Substanzen die thermomikroskopischen Konstanten mitgeteilt und die gegebenenfalls notwendigen Zusatzreaktionen beschrieben. Bei Nicotinamid, das auf Grund seiner Fähigkeit, mit vielen Stoffen wie organischen Säuren, Säureestern, Phenolen u. a. Komplexverbindungen zu bilden, häufig als Reagens in Betracht kommt, wird das polymorphe Verhalten erläutert und das Auftreten von sieben Modifikationen beschrieben.

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Contribution to the microscopic identification of organic materials after L. Kofler. V

Summary In continuation of earlier investigations for the purpose of supplementing and extending the identification tables ofKofler, the thermomicroscopic constants are given for 62 substances and when necessary the supplementary reactions are described. In the case of nicotinamide, which because of its ability to yield among other things complex compounds with organic acids, acid esters, phenols, is frequently considered as reagent, the complex behavior is illustrated and the occurrence of 7 modifications is described.

     

Tritium volume activity in natural waters of the NPP Temelín region

With the use of the tritium monitoring network the samples of river water, air humidity and precipitation are collected and analysed for HTO in the vicinity of Temelín nuclear power plant.     

Determination of iron at ng/ml level by solid phase spectrophotometry after preconcentration on cation exchange filters

A cationic exchanger paper is used to retain analytes in solution and, after drying, to analyze directly by measuring the UV-Vis absorbance of the paper. The method was applied to determination of iron using its known 1,10-phenanthroline complex. Using 100 ml of sample the applicable concentration range was between 1.0 and 10.0 ng/ml with a detection limit of 0.2 ng/ml and a RSD around 2%. The method was applied to determination of iron total in snow, human serum and wine.     

Gold(III) complexes with imidazole,benzoxazole, purine and pyrimidine derivatives

Summary The synthesis and characterization of Au^III complexes with several heterocyclic ligands are reported. The compounds have general formula [AuX₃(L)], where L =N-methylimidazole (N-MeIz),N-ethylimidazole (N-EtIz),N-propylimidazole (N-PrIz), benzoxazole (BO), 2-methylbenzoxazole (2-MeBO), 2,5-dimethylbenzoxazole (2,5-diMeBO), 2-amino-pyrimidine (2-APm), 4(6) -hydroxy-pyrimidine [4(6)-hydrPm] or hypoxanthine (Hypox) and X = Cl or Br. Elemental analysis, conductivity measurements and spectral studies were used for the characterization of the complexes. A square-planar geometry withN-bonded heterocyclic ligands is suggested.     

Nucleocyclitols. Synthesis of substituted purinyl-muco-inositol derivatives

Several carbocyclic nucleoside analogs possessing a 6-substituted purine linked to a mesylated muco-inositol were synthesized. The coupling of triethylamine-activated 6-chloropurine with 2,3-anhydro-l,5,6-tri-O-(methanesulfonyl)-epi-inositol gave a 6-chloro purinyl muco-inositol amenable to further synthetic transformations in the heterocyclic moiety by substitution of the chlorine atom by nitrogen nucleophiles such as methylamino, diethylamino, benzylamino, hydrazino, morpholino, hydroxylamino, piperidino, and glycyl groups.     

Study of the drying zirconia gel-precipitates using thermal analysis

Thermoanalytical techniques (TG, DTG, DTA and EGA) can be helpful in studying gel compositions and relating the chemical history and the role of the precipitant to the chemical properties of gels. The objective of our work was to determine the influence of the initial conditions in the reaction mixture on the product characteristics. Zirconia gels were prepared by the gelprecipitation method by the hydrolysis of zirconium tetrachloride dissolved in methanol. The substitution of water by methanol was chosen in order to obtain a reaction medium in which better control of the hydrolysis and condensation reactions of the zirconium precursor were achieved and thus also better control of the final properties of the dried zirconia gel-precipitates could be obtained. The nature of the hydrated zirconia gels obtained during the gelation process is strongly influenced by the conditions of the reaction mixture, e.g. concentration of the zirconium precursor, the mixing rate and particularly by the amount of water added. To distinguish between various types of water in the gel-precipitates, the furnace atmosphere and the partial water pressure were altered appropriately. It was shown that initial zirconium to water molar ratio has a significant effect on the properties of the final products. It was assumed that, according to the preparation conditions, three different types of water are present in the formed zirconia gel-precipitates. Modification of the dehydration processes of zirconia gel-precipitates enables control of the final microstructural and surface properties of the dried gels which are suitable for further catalysts support as well as mixed oxide preparation.     

Some applications of gel-permeation chromatography in investigations of structure and the solution properties of radical-initiated poly(vinyl chloride)

The applicability of the published universal calibration parameters for gel-permeation chromatography on polystyrene standards and poly(vinyl chloride) samples with a defined structure has been compared. It was shown experimentally that of several theoretically possible molecular weight averages attributed to the elution volume at the position of the peak maximum, the root mean-square average molecular weight M _Rms = (M _wM _n)^0.5 shows the best accordance. The molecular weights obtained by gel-permeation chromatography were compared with those determined by viscometry, osmometry, and the light-scattering method. The reproducibility of gel-permeation chromatography measurements is 3%, and the average variance of the results as compared with results obtained by the above methods is about 8%. It was also found that the gel-permeation chromatography does not involve any anomalies interfering with results obtained by other methods.     

On-line preconcentration of inorganic mercury and methylmercury in sea-water by sorbent-extraction and total mercury determination by cold vapour atomic absorption spectrometry

A comparative study of three mercury chelate forming reagents [diethyldithiocarbamate, pyrrolidin-1-yldithioformate and diphenylthiocarbazone (dithizone)] has been carried out for the preconcentration of ultratrace amounts of inorganic mercury and methylmercury in silica C(18) minicolumns as the solid sorbent. Sample flow injection in-line sorbent extraction was coupled with continuous cold vapour atomic absorption spectrometry (CVAAS) for detection. Results showed the superiority of the carbamate type reagents over the dithizone for the on-line formation and preconcentration of the corresponding mercury chelates. Using diethyldithiocarbamate (DDC) as reagent, aqueous sample volumes of 100 ml can be preconcentrated with 100% efficiency for both inorganic mercury and methylmercury. Quantitative release of the retained DDC chelates was obtained for volumes of eluent (ethanol) of 50 microl. Following the proposed procedure, detection limits of 16 ng/l. of mercury were achieved for sample volumes of 25 ml. The relative standard deviation was +/- 3.4% at 0.5 microg/l. Hg(II) levels. The method has been successfully applied to the determination of low levels of mercury in sea-water.