Crystallic silver amalgam--a novel electrode material

A crystallic silver amalgam was found to be a suitable working electrode material for voltammetric determination of electrochemically reducible organic nitro-compounds. Optimum conditions for crystal growth were found, the crystal surface was investigated by atomic force microscopy in tapping mode and single crystals were used for the preparation of quasi-cylindrical single crystal silver amalgam electrode (CAgAE). An electrochemical behavior of this alternative electrode material was investigated in aqueous media by direct current voltammetry, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and adsorptive stripping voltammetry (AdSV) using 4-nitrophenol as a model compound. Applicable potential windows of the CAgAE were found comparable with those obtained at a hanging mercury drop electrode, providing high hydrogen overpotential, and polished silver solid amalgam electrode. Thanks to the smooth single crystal electrode surface, the effect of the passivation is not too pronounced, direct DPV determination of 100 μmol l(-1) of 4-nitrophenol at CAgAEs in 0.2 mol l(-1) acetate buffer pH 4.8 provides a RSD around 1.5% (n = 15). DPV calibration curves of 4-nitrophenol are linear in the whole concentration range 1-100 μmol l(-1) with a limit of quantification of 1.5 μmol l(-1). The attempt to increase sensitivity by application of AdSV was not successful. The mechanism of 4-nitrophenol reduction at CAgAE was investigated by CV.     

Inhibition effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria during sludge liquor treatment: influence of feeding strategy

The importance of feeding strategy for the long-term selective inhibition of nitrite-oxidising bacteria (NOB) was demonstrated by comparison of laboratory-scale bioreactors: Completely Stirred Tank Reactor (CSTR) and Sequencing Batch Reactor (SBR). Moreover, the effect of the change of reactor operation regime from CSTR to SBR was demonstrated. Sludge liquor containing ammonia nitrogen in a range of 970–1500 mg L^?1 was the influent of the reactors. The experiments were performed at (23 ± 2)°C, with high concentration of dissolved oxygen (up to 8 mg L^?1) and with unlimited sludge retention time. In the SBR, permanent restriction of NOB activity was achieved for more than 700 days by the strong inhibition effect of fluctuating concentrations of free ammonia and free nitrous acid during the operational cycles of SBR. In contrast, nitrite-oxidising bacteria were able to gradually adapt to the conditions prevailing in CSTR and produce nitrate although the concentration of free ammonia and free nitrous acid significantly exceeded inhibition limits for NOB activity in this system. Transferring the reactor operation regime from CSTR to SBR resulted in immediate and permanent inhibition of NOB activity in the reactor.     

Examination of a procedure for the production of a simulated filter-based air particulate matter reference material

An approach for producing simulated air particulate matter (APM) deposited on filters has been developed and investigated as to its usefulness for yielding large batches of filters as a future reference material. The APM deposited on the filters was a material collected from an urban industrial area, and had been milled to approximate a material of PM-2.5 particle size distribution. The milled APM material was loaded onto filter substrates (Nuclepore) through the deposition of aliquots from a liquid suspension via vacuum filtration. It should be noted that these filters do not represent a typical PM-2.5 elemental composition, since the milling increased the proportion of crustal materials and the suspension in liquid decreased the sulfate content. Homogeneity between filters was tested using INAA (whole filter analysis) and ED-XRF and PIXE and was estimated to be in the 5% range (relative standard deviation). Homogeneity within the filters and among the filters was also tested using micro-XRF and found to be acceptable for the elements tested. The results of the tests carried out on the filters indicate that this approach is appropriate for large-scale production of similar filters for distribution as reference materials.     

The synthesis and transformations of some 3-thiocarbamoylthiazolidines

In connection with our studies on potential bioactive compounds some new polysubstituted 3-thiocarbamoylthiazolidines 5, 6, 7, 9 and 10 were prepared in the reaction between 2-(2-methoxy-phenyl)iminothiazolidine (2) and sulfamoylphenyl isothiocyanates 3 and 4a-c. The structures for compounds 2 and 5 were established by X-ray analyses, showing that the reaction is taking place at the endo-cyclic nitrogen atom of thiazolidine ring.     

Elastic interaction between two parallel dislocations in non-parallel slip planes

The elastic interaction between two parallel dislocations which can glide in non-parallel slip planes is studied under the simplifying assumption that the dislocation glide velocity is proportional to stress. The motion of the two dislocations is represented by a motion of one reference point in a configuration plane. It is concluded that the contribution of the long-range elastic interaction between individual dislocations from different slip systems to work hardening is negligible, compared to the contribution from the formed attractive junctions. Especially, two parallel edge dislocations with mutually perpendicular Burgers vectors can co-exist in minimum energy positions, however, they can be separated by an arbitrarily small external stress.     

Emanation thermal analysis for characterizing diffusion properties of Ba-phthalate, -isophthalate and -terephthalate

Emanation thermal analysis (ETA) is used for characterizing Ba-salts of phthalic, isophthalic and terephthalic acids. It is shown that the manation thermal characteristics measured in the temperature range between 298 and 373 K are suitable for estimating diffusion properties of studied organic solids. The ETA results are supplied by TG/DTG and DTA curces and surface area measurements. An apparatus for determining emanation-thermal characteristics is proposed.     

Determination of anabolic steroids in creatine nutritional supplements after supercritical fluid extraction

The effects of various parameters, i.e. extraction pressure, temperature, time, and modifier on the efficiency of extraction were investigated using an analytical-scale supercritical fluid extraction system. An optimal set of conditions for the extraction and determination by gas chromatography-mass spectrometry of trimethylsilyl derivatives of 4-androstene-3,17-dione, 1,4-androstadiene-3,17-dione, nandrolone, and testosterone in nutritional supplements was developed. The optimum amount of creatine supplement was 1 g, while the optimum pressure and temperature were determined to be 35 MPa and 80 °C, respectively. The optimum dynamic extraction time was 45 min. The limit of detection (LOD) of the investigated compounds ranged from 5 to 25 ng · g⁻¹ of supplement, while recoveries ranged from 76.1 to 86.6%. Correspondence: Petra Mikulcikova, Department of Analytical Chemistry, Faculty of Chemical Technology, University of Pardubice, nám. Cs. Legií 565, CZ 532 10 Pardubice, Czech Republic