Determination of ammonium,calcium, magnesium,potassium and sodium in drinking waters by capillary zone electrophoresis on a column-coupling chip

This work deals with simultaneous determination of ammonium, calcium, magnesium, sodium and potassium in drinking waters by capillary zone electrophoresis (CZE) on a column-coupling (CC) chip with suppressed hydrodynamic and electroosmotic transports. CZE separations were carried out in a propionate background electrolyte at a low pH (3.2) containing 18-crown-6-ether (18-crown-6) to reach a complete resolution of the cations. In addition, triethylenetetramine (TETA) coated the inner wall surface of the chip channels. The concentration limits of detection (cLOD) for the studied cations ranged from 4.9 to 11.5 μg/l concentrations using a 900 nl volume of the sample injection channel. 93–106% recoveries of the cations in drinking waters indicate a good predisposition of the present method to provide accurate analytical results.     

Recovery and pre-concentration of gold onto poly((N-(Hydroxymethyl)methacrylamide)–1-allyl-2-thiourea) hydrogels synthesized by gamma radiation

Poly((N-(Hydroxymethyl)methacrylamide)–1-allyl-2-thiourea) hydrogels, Poly(NHMMA–ATU), were synthesized by gamma radiation using ⁶⁰Co γ source at different irradiation doses and different ATU content in the irradiated monomer mixture. The swellability of the synthesized hydrogels was changed by irradiation doses and by the content of ATU in the irradiated mixture. These hydrogels were used for the specific gold recovery and pre-concentration from single gold ion solutions and from different natural samples. It has been observed that gold adsorption capacity onto the hydrogels was high at low pHs and reached maximum value at pH = 0.5. Adsorption capacity of the hydrogels for gold at pH = 0.5 was found to be about 698 mg g^− 1 dry hydrogels. Adsorption equilibrium time of gold ions onto the hydrogels was found to be very short and also these hydrogels were showed extremely high selectivity to the gold ions in acidic media when the concentration of the other metal ions were extremely higher than gold. Because of the high specificity of these hydrogels to gold beside the other metal ions at low pHs, all matrix effects were easily eliminated adsorbing gold onto the hydrogels and desorbing into 3 M HCl solution containing 0.8 M thiourea. These hydrogels were found to be highly open pore size. This property of the hydrogels make them attractive due to high adsorption capacity of gold ions on/in the hydrogels penetrating inside and react to all functional groups in the interior surface of the hydrogels.     

X-ray structural analysis, antioxidant and cytotoxic activity of newly synthesized salicylic acid derivatives

New salicylic (2-hydroxybenzoic) acid derivatives 1–6 were prepared by conventional heating or microwave irradiation of a mixture consisting of methyl salicylate and the corresponding amino alcohol (2,2′-dihydroxydiethylamine, 2,2′,2″-trihydroxytriethylamine or N-phenyl-2,2′-dihydroxydiethylamine) and metallic sodium as catalyst. For compounds 1, 3, and 5 X-ray structure analysis was performed, as well as molecular mechanics calculations (MMC), to define their conformation in terms of their energy minima. Comparison of crystal and MMC structures for these three compounds (1, 3, and 5) revealed that the intramolecular hydrogen bonds play an important role, stabilizing conformation of the most part of the molecule. The antioxidant activity and cytotoxicity of the synthesized derivatives were evaluated in a series of in vitro tests. The newly synthesized compounds exhibited strong activity against hydroxyl radical, as well as promising lipid peroxidation inhibition. The study showed that the electronic effects of the groups at the N atom are responsible for neutralization of the OH radical, i.e., antioxidant activity. Compounds 1–3 exhibited sub-micromolar cytotoxicity against HeLa S3, whereas compounds 1, 3 and 5 efficiently inhibited the growth of PC3 cells.     

7‐Amino‐5‐methyl‐2‐phenyl‐6‐(phenyldiazenyl)pyrazolo[1,5‐a]pyrimidine crystallizes with Z′ = 2: pseudosymmetry and the formation of complex sheets built from N—H...N and C—H...π(arene) hydrogen bonds

The title compound, C₁₉H₁₆N₆, crystallizes with Z′ = 2 in the space group P2₁/n. The two molecules in the selected asymmetric unit are approximate mirror images of one another; most corresponding pairs of atoms are related by an approximate half‐cell translation along [100]. Each molecule contains an intramolecular N—H...N hydrogen bond and the molecules are linked into complex sheets by a combination of two intermolecular N—H...N and four C—H...π(arene) hydrogen bonds. Comparisons are made with some other 7‐aminopyrazolo[1,5‐a]pyrimidines.     

Highly selective catalytic nitration of 1-nitronaphthalene with NO2 to 1,5-dinitronaphthalene over solid superacid SO42−/ZrO2 promoted by molecular oxygen and acetic anhydride under mild conditions

A simple and efficient method for liquid-phase catalytic nitration of 1-nitronaphthalene with NO₂ to 1,5-dinitronaphthalene under mild conditions has been developed. The results indicated that the sulfated zirconia (SO₄^2?/ZrO₂) as solid superacid catalyst exhibits superior catalytic performance with dioxygen and acetic anhydride. 93.8% conversion of 1-nitronaphthalene and 52.8% 1,5-dinitronaphthalene selectivity were achieved. Furthermore, the physicochemical properties of SO₄^2?/ZrO₂ were determined by XRD, Py-FT-IR, BET, FT-IR, Raman spectroscopy and ICP-OES technologies. The possible nitration reaction mechanism over SO₄^2?/ZrO₂ catalyst was proposed. The present work provides an easy-to-implement, mild and eco-friendly approach for the efficient preparation of valuable 1,5-dinitronaphthalene, which has extensive industrial application prospects.

     

Determination of iron and lead by flame atomic absorption spectrometry after preconcentration with sepiolite

By using a new adsorbent (sepiolite) an adsorption-elution and atomic absorption spectrometric method has been developed for the preconcentration and determination of Fe and Pb. Recoveries of the analytes were 82 ± 3% for Fe and 91 ± 2% for Pb at 95% confidence level. For Cu it was only 5 ± 1%. The recovery of iron could be increased to about 97 ± 1% by complexing with EDTA, the recovery of copper only to 57 ± 2%. The optimised method was applied to the determination of lead in metal materials (e.g. brass). Received: 20 February 1996 / Revised: 7 May 1996 / Accepted: 11 May 1996     

Phase formation and thermal stability of the compounds in the Bi2O3-PbO system

The scientific interest for the Bi₂O₃-PbO system has increased due to the importance of the PbO in the high-T _c superconducting phase formation in the Bi₂O₃-SrO-CaO-CuO system. Also Bi₂O₃-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi₂O₃-based solid solutions are well known as high oxygen ion conductors.Previously, several low melting defined compounds have been identified in the system: 6Bi₂O₃·PbO; 3Bi₂O₃·2PbO; 4Bi₂O₃·5PbO; 4Bi₂O₃·6PbO and Bi₂O₃·3PbO.This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi₂O₃/PbO ratio, the compound 6Bi₂O₃·PbO is preferentially formed, followed by the compound 4Bi₂O₃·5PbO. The formation of the compound 4Bi₂O₃·6PbO was not confirmed while the formation of the compound Bi₂O₃ 3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.     

Joint economic design of EWMA control charts for mean and variance

Control charts with exponentially weighted moving average (EWMA) statistics (mean and variance) are used to jointly monitor the mean and variance of a process. An EWMA cost minimization model is presented to design the joint control scheme based on pure economic or both economic and statistical performance criteria. The pure economic model is extended to the economic-statistical design by adding constraints associated with in-control and out-of-control average run lengths. The quality related production costs are calculated using Taguchi’s quadratic loss function. The optimal values of smoothing constants, sampling interval, sample size, and control chart limits are determined by using a numerical search method. The average run length of the control scheme is computed by using the Markov chain approach. Computational study indicates that optimal sample sizes decrease as the magnitudes of shifts in mean and/or variance increase, and higher values of quality loss coefficient lead to shorter sampling intervals. The sensitivity analysis results regarding the effects of various inputs on the chart parameters provide useful guidelines for designing an EWMA-based process control scheme when there exists an assignable cause generating concurrent changes in process mean and variance.     

Coordination of staffing and pricing decisions in a service firm

Customer demand is sensitive to the price paid for the service in many service environments. Using queueing theory framework, we develop profit maximization models for jointly determining the price and the staffing level in a service company. The models include constraints on the average waiting time and the blocking probability. We show convexity of the single‐variable subproblem under certain plausible assumptions on the demand and staffing cost functions. Using numerical examples, we investigate the sensitivity of the price and the staffing level to changes in the marginal service cost and the user‐specified constraint on the congestion measure. Copyright © 2008 John Wiley & Sons, Ltd.