Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam

A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l⁻¹, and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis.     

Preparation and characterization of Mg(II)-, Ca(II) and Cd(II) complexes of 1,2-ethanediol and water

Mixed ligand complexes of different compositions were prepared with water, sulfate ion and 1,2-ethanediol as ligand. IR spectra and the thermoanalytical curves of the complexes were recorded. Oxygen atoms bound by one or two coordinate bonds to the metal ion, or by hydrogen-bonds in the crystal, were observed. As for the water molecule, 1,2-ethanediol molecules of crystal and monohydrate type were found, depending on the type of binding of the oxygen atoms.This revised version was published online in November 2005 with corrections to the Cover Date.     

A study of the polarographic behaviour of meso-tetra(4-trimethylammoniumphenyl)porphine and its copper and magnesium complexes and its analytical applications

The investigation of the electrochemical reduction and the adsorption of meso-tetra(4-trimethylammoniumphenyl)porphine (T(4-TMAP)P) at a mercury electrode in alkaline solution shows that the overall reduction involves three two-electron steps, of which the first step is reversible and the latter two are irreversible. In addition, T(4-TMAP)P and its metal complexes of Cu(II) and Mg(II) can be strongly adsorbed on the surface of a mercury electrode. The adsorption phenomena have been utilized as a preconcentration step for the determination of trace amounts of the two ions by single sweep polarography. For copper, the detection limit is 1 × 10^–8 mol dm^–3, for magnesium, 1 × 10^–7 mol dm^–3, the latter being limited by the reagent blank. The proposed method was applied to the determination of Cu and Mg in various types of samples (chemicals, hair and liver tissues) with satisfactory results.     

Direct calculation of ionization potentials of closed-shell atoms and molecules

Vertical ionization potentials, electron affinities and information about quasi-particles can be obtained by using the technique of the single-particle propagator. The expansion of the self-energy part up to third order perturbation theory can be evaluated numerically, but does not lead, in most cases, to satisfying results. A theoretical and numerical analysis of the diagrammatic expansion of the self-energy part requires the introduction of a renormalized interaction and renormalized hole and particle lines.     

HPLC Analysis of Cotinine in Urine After SPE with a Cholesterol-Modified Adsorbent

A one-step solid-phase extraction procedure, based on a new silica gel adsorbent modified with cholesterol groups, has been investigated for measurement of cotinine in urine. Cotinine is the main metabolite of nicotine in the human body and is analyzed as a biomarker for assessment of direct or passive exposure to tobacco smoke. New cholesterol-modified adsorbents have been obtained by chemical modification of silica gel of different porosity with cholesterol ligands. Although recovery by this extraction procedure were optimum over a relatively broad range of sample pH (3.1–8.0), analytical conditions such as sample loading, washing and elution conditions, concentration of cotinine to be extracted, and the type of adsorbent used for extraction were found to affect the efficiency of the procedure and had to be controlled for optimum recovery. When these conditions were controlled, recovery of cotinine from spiked human urine was reproducible and depended on compound ionization. Quantitative analysis of cotinine was performed by reversed-phase high-performance liquid chromatography with UV detection. Presented at: Conference of the Hyphenation of Liquid Chromatography–Nuclear Magnetic Resonance Spectroscopy, Liquid Chromatography–Mass Spectrometry and Related Topics, Tuebingen, Germany, March 25–29, 2006.     

Reaction of cyclopentadienyllutetium anthracenide with azobenzene. Synthesis and molecular and crystal structure of the binuclear complex [C5H5(THF)Lu(μ−η2:η2−PhN—NPh)]2(THF)2 and its dynamic behavior in solution

The reaction of the cyclopentadienyllutetium anthracenide, C₅H₅Lu(C₁₄H₁₀)²⁻(THF)₂ (1), with azobenzene yielded the [C₅H₅(THF)Lu(μ−η²:η²−PhN—NPh)]₂(THF)₂ (2) binuclear complex. The structure of the reaction product was established by X-ray structural analysis. The dynamic behavior of complex2 in a THF-d₈ solution was studied by¹H NMR spectroscopy in the temperature range of 265–330 K. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1667–1671, September, 1997.     

Quantum chemical studies on electrophilic addition

The geometries of the 2-chloroethyl and ethylenechloronium cations, two possible intermediates in the electrophilic addition of chlorine to ethylene, have been fully optimized using ab initio molecular orbital calculations employing the split valence shell 4-31G basis set.These geometries were then used to compute more accurate wave functions using Dunning's double-zeta basis set. The bridged chloronium ion was found to be more stable by 9.35 kcal/mole, the opposite order of stability from the C₂H₄F⁺ ions. Interconversion of the two C₂H₄Cl⁺ cations was computed to have a barrier of 6.25 kcal/mole.The activation energy for this chlorination reaction, using the ethylenechloronium cation and a chlorine anion at infinite separation as the model for the activated complex, was computed to be 128.7 kcal/mole, showing that this is not a feasible gas phase reaction.     

Lipids from Five Cotton Varieties

Seed characteristics and the lipid and fatty-acid compositions were determined for the new cotton varieties ASh-25, Omad, 9771-I, Termez-43, and Bukhara-6.     

Palladium-catalyzed ring expansion reaction of 1-alkynylcyclobutanols with aryl iodides: an efficient route to 2-disubstituted methylenecyclopentanones

The reaction of 1-alkynylcyclobutanols with aryl iodides in the presence of Pd(OAc)₂ and Et₃N in acetonitrile at 80°C for 24 h gives 2-disubstituted methylenecyclopentan-1-ones in modest to good yields. The tandem insertion-ring expansion process proceeds via the formation of an alkynyl π-complex, followed by migration of a carbon-carbon bond of the tert-alkanol to form the cyclopentanones stereoselectively.     

LC-ESI-MS Determination of Bilobalide and Ginkgolides in Canine Plasma

A sensitive and selective method using liquid chromatography with electrospray ionization mass spectrometric detection was developed for the quantification of bilobalide and ginkgolides in canine plasma. The analytes were extracted with diethyl ether-dichloromethane-isopropanol (6:3:1, v/v) after spiking the samples with daidzein (internal standard). The lower limit of quantification (LLOQ) of the method was 2.5 μg L⁻¹ for ginkgolide B and 10.0 μg L⁻¹ for bilabolide, ginkgolide A and ginkgolide C. The accuracy of the method was within 15% of the actual values over a wide range of plasma concentrations. The intra-day and inter-day precision was better than 15% (R.S.D.). Finally, the LC-ESI-MS method was successfully applied to study the pharmacokinetics of ginkgolides and bilabolide after administration of Ginkgo biloba extracts to dogs.