Kinetic spectrophotometric determination of trace amounts of selenium and vanadium

A sensitive kinetic spectrophotometric method has been developed for the determination of Se(IV) over the range of 45 to 4000 ng in 10 mL of solution. The method is based on the catalytic effect of Se(IV) on the reduction reaction of bromate by hydrazinium dichloride, with subsequent reaction of Ponceau S with products of the above reaction (chlorine and bromine), causing color changing of Ponceau S. Method development includes optimization of time interval for measurement of slope, pH, reagents concentration, and temperature. The optimized conditions yielded a theoretical detection limit of 33 ng/?10 mL of solution of Se(IV). The interfering effects were studied and removed. The method was applied to the determination of selenium in spiked water, Kjeldahl tablet, selenium tablet, and shampoo. Vanadium(V) has an inhibition effect on the catalyzed reaction of bromate and hydrazine by selenium. Using this effect, V(V) can be determined in the range of 70 to 2500 ng in 10 mL of solution. The optimization procedure includes pH and selenium concentration. An extraction method was used for interference removal. The method was applied to the determination of vanadium in petroleum. Received: 20 October 1998 / Revised: 17 April 1999 / Accepted: 3 June 1999     

Correction to: Design,fabrication, and characterization of thermal and optical properties of nano‑composite self‑cleaning smart window

Optical and Quantum Electronics - Optical properties of polymerized polyethylene layers deposited on glass substrates by PECVD technique at different radio frequency powers are studied through...     

Solvent Effects on Tautomeric and Microscopic Protonation Constants of Glycine in Different Aqueous Solutions of Methanol and Ethanol

The acid-base equilibria of glycine have been studied in different aqueous solutions of methanol and ethanol (0?C45?% v/v) using a potentiometric method. In this study, the macro and micro protonation constants of the amino acid and its tautomeric constant have been determined at 25?°C and constant ionic strength (0.1 mol?dm^?3 NaClO₄). The protonation and the tautomeric constants of glycine in different binary mixtures were analyzed in terms of the Kamlet, Abboud and Taft (KAT) parameters. Single-parameter correlations of the constants versus ?? (hydrogen-bond donor acidity), ?? (hydrogen-bond acceptor basicity) and ?? ^? (dipolarity/polarizability) are poor in all solutions. Multi-parameter correlations show better results, but dual-parameter correlations represent significant improvements with regard to the single- and multi-parameter models. Linear correlation is observed when the experimental protonation constant values are plotted versus the calculated ones when the KAT parameters are considered. Finally, the results are discussed in terms of the effect of the solvent on protonation and tautomeric constants.     

In vitro antibacterial activity of some Iranian medicinal plant extracts against Helicobacter pylori

Helicobacter pylori infection causes lifelong chronic gastritis, which can lead to peptic ulcer, mucosa-associated lymphoid tissue (MALT) lymphoma and gastric cancer. The growing problem of antibiotic resistance by the organism demands the search for novel candidates from plant-based sources. In the present study, we evaluated the in vitro anti-H. pylori activity of some selected medicinal plants on clinical isolates of H. pylori. Gastric biopsy samples were obtained from patients presenting with gastroduodenal complications. Helicobacter pylori was isolated from the specimens following standard microbiology procedures. The disc-diffusion method was used to determine the susceptibility of three H. pylori isolates to methanol extracts of 23 Iranian plants. All tests were performed in triplicate. Among them, the extracts of Punica granatum and Juglans regia had remarkable anti-H. pylori activity with mean of inhibition zone diameter of 39 and 16?mm at 100?μg?disc?1, respectively. In view of the results obtained with P. granatum (pomegranate), the peel extracts of nine cultivars of pomegranate (Shirin-e-Pust Sefid, Agha Mohammad Ali-e-Shirin, Sefid-e-Shomal, Sefid-e-Torsh, Shirin-e-Malase, Tabestani-e-Torsh, Shirin-e-Saveh Malase, Alak-e-Shirin, Pust Siyah) were further assayed against the clinical isolates of H. pylori. The results revealed that all Iranian pomegranate cultivars, except for Alak-e-Shirin, showed significant in vitro anti-H. pylori activity against the clinical isolates of H. pylori (mean of inhibition zone diameter ranging from 16 to 40 mm at 50 μg disc?1).     

Single-walled carbon nanotubes as stationary phase in gas chromatographic separation and determination of argon, carbon dioxide and hydrogen

A chromatographic technique is introduced based on single-walled carbon nanotubes (SWCNTs) as stationary phase for separation of Ar, CO₂ and H₂ at parts per million (ppm) levels. The efficiency of SWCNTs was compared with solid materials such as molecular sieve, charcoal, multi-walled carbon nanotubes and carbon nanofibers. The morphology of SWCNTs was optimized for maximum adsorption of H₂, CO₂ and Ar and minimum adsorption of gases such as N₂, O₂, CO and H₂O vapour. To control temperature of the gas chromatography column, peltier cooler was used. Mixtures of Ar, CO₂ and H₂ were separated according to column temperature program. Relative standard deviation for nine replicate analyses of 0.2 mL H₂ containing 10 μL of each Ar or CO₂ was 2.5% for Ar, 2.8% for CO₂ and 3.6% for H₂. The interfering effects of CO, and O₂ were investigated. Working ranges were evaluated as 40-600 ppm for Ar, 30-850 ppm for CO₂ and 10-1200 ppm for H₂. Significant sensitivity, small relative standard deviation (RSD) and acceptable limit of detection (LOD) were obtained for each analyte, showing capability of SWCNTs for gas separation and determination processes. Finally, the method was used to evaluate the contents of CO₂ in air sample.     

Colloidal Nanogold-Based Immunochromatographic Strip Test for the Detection of Digoxin Toxicity

Digoxin is widely used as a cardiac glycoside drug in the treatment of various heart conditions. Because it is a toxic drug, it should be regularly monitored in the serum of patients under treatment. In this study, colloidal nanogold is synthesized and the preparation of nanogold-labeled monoclonal antibody probe to digoxin is described under optimal conditions. In addition, an immunochromatographic (IC) method for digoxin analysis employing nanogold-labeled probe is developed. With this technique, it requires only 5 min to complete the quantitative detection of digoxin. The detection time is decreased 20–30 times in comparison to radioimmunoassay (RIA). The sensitivity to digoxin was about 2 ng/ml by naked eye, which is within the therapeutic and toxic ranges of digoxin. The results of serum samples obtained by IC strip were in agreement with those obtained by RIA. The IC strip was sufficiently sensitive and accurate to be used for the rapid detection of digoxin in serum samples.     

Thermodynamics of the ternary systems: (water + glycine,l-alanine and l-serine + di-ammonium hydrogen citrate) from volumetric,compressibility, and (vapour + liquid) equilibria measurements

The apparent molar volumes and isentropic compressibility of glycine, l-alanine and l-serine in water and in aqueous solutions of (0.500 and 1.00) mol · kg^?1 di-ammonium hydrogen citrate {(NH₄)₂HCit} and those of (NH₄)₂HCit in water have been obtained over the (288.15 to 313.15) K temperature range at 5 K intervals at atmospheric pressure from measurements of density and ultrasonic velocity. The apparent molar volume and isentropic compressibility values at infinite dilution of the investigated amino acids have been obtained and their variations with temperature and their transfer properties from water to aqueous solutions of (NH₄)₂HCit have also been obtained. The results have been interpreted in terms of the hydration of the amino acids. In the second part of this work, water activity measurements by the isopiestic method have been carried out on the aqueous solutions of {glycine + (NH₄)₂HCit}, {alanine + (NH₄)₂HCit}, and {serine + (NH₄)₂HCit} at T = 298.15 K at atmospheric pressure. From these measurements, values of vapour pressure, osmotic coefficient, activity coefficient and Gibbs free energy were obtained. The effect of the type of amino acids on the (vapour + liquid) equilibrium of the systems investigated has been studied. The experimental water activities have been correlated successfully with the segment-based local composition Wilson model. Furthermore, the thermodynamic behaviour of the ternary solutions investigated has been studied by using the semi-ideal hydration model and the linear concentration relations have been tested by comparing with the isopiestic measurements for the studied systems at T = 298.15 K.     

The Effect of Lateral Guiding Mechanism on Noise Characteristics in Semiconductor Lasers

A comparison between intensity noise spectra and also the line shapes of gain-guided, weakly-index-guided, and strongly-index-guided semiconductor lasers are made using numerical solution of Maxwell-Bloch equations including spontaneous emission noise.