Simultaneous determination of organotin,organolead, and organomercury compounds in environmental samples using capillary gas chromatography with atomic emission detection

As part of a continuing evaluation of new analytical and sample preparation techniques conducted by the US Environmental Protection Agency (EPA), the use of capillary gas chromatography with atomic emission detection (GC-AED) for the simultaneous determination of organotin, organolead, and organomercury compounds in environmental samples was investigated. Pentylmagnesium bromide was used to pentylate ionic organotin, organolead, and organomercury compounds; the pentyl derivatives were then separated by GC and determined by AED. Several important GC-AED parameters, including the type of injector inlet, carrier gas flow rate, and helium make-up gas flow rate, were optimized for the simultaneous determination of these organometallic compounds. Their minimum detectable concentrations were approximately 1.0 to 2.5 ng/mL using a 0.5-μL on-column injection. The calibration curves exhibited good linearity between 2.5 and 2500 ng/mL for organotin and organolead compounds, and between 2.5 and 10000 ng/mL for organomercury compounds.     

POLYMER—SUPPORTED SINGLE AND MIXED AMMONIUM AND PHOSPHONIUM SALTS AS CATALYSTS FOR PHASE—TRANSFER REACTIONS

In this study was to investigate,by phase-transfer catalysis,the activity of single and mixed ammonium and phosphonium salts grafted on a “gel-type“ stryene-7% divinylbenzene copolymer in the oxidation of benzyl alcohol with hydrogen peroxide.A wide variety of catalysts with different quaternary groups and different quaternary chain length substitutents were examined.The activity of single“onium“salts increases as a consequence of the association of ammonium and phosphonium salts grafted onn the same polymeric support.The activity of polymer-supported ammonium and phosphonium salts increases with the number of carbon atoms contained in the alkyl radicals of the -onium and of the functionalization degree with phosphonium groups.     

Supercritical fluid extraction of kava lactones from Piper methysticum (kava) herb

Supercritical fluid extraction of kava lactones from Piper methysticum Forst. herb is described here. The extraction was performed with supercritical carbon dioxide alone and supercritical carbon dioxide modified with 15% ethanol, and the extracts were analyzed by gas chromatography/mass spectrometry. Seven lactones including: 7,8-dihydrokavain; kavain; 5,6-dehydrokavain; 5, 6, 7, 8-tetrahydroyangonin; dihydromethysticin; yangonin; and methysticin were the major constituents in the SFE extract.     

Sodium Trihydrogen-1,4-Benzenediphosphonate: An Extended Coordination Network

Abstract  

Crystals of sodium trihydrogen-1,4-benzenediphosphonate, Na[H₃bdp], were prepared from the addition of aqueous sodium hydroxide to an acidified solution of 1,4-benzenediphosphonic acid (H₄bdp). These were shown by X-ray crystallography to crystallize in the space group P [`1] bar{1} , with cell parameters a = 5.7500(3) ?, b = 7.9180(5) ?, c = 10.4420(6) ?, α = 80.398(3)°, β = 76.844(4)° and γ = 81.389(4)°. The crystal structure revealed that the title compound forms a coordination network in which sodium-phosphonate sheets are pillared by the benzene rings into a three-dimensional structure.     

Above-threshold ionization of hydrogen and hydrogen-like ions by X-ray pulses

This paper adresses the problem of above-threshold ionization (ATI) of hydrogen interacting with an intense X-ray electromagnetic field. Two approaches have been used. In the first approach, we calculate generalized differential and total cross sections based on second-order perturbation theory for the electron interaction with a monochromatic plane wave, with the A ² and A · P contributions from the nonrelativistic Hamiltonian (including retardation) treated exactly. In the second approach, we solve the time-dependent Schrödinger equation (TDSE) for a pulsed plane wave using a spectral approach with a basis of oneelectron orbitals, calculated with L ²-integrable B-spline functions for the radial coordinate and spherical harmonics Y _lm for the angular part. Retardation effects are included up to O(1/c), they induce extra terms forcing the resolution of the TDSE in a three dimensional space. Relativistic effects [of O (1/c ²)] are fully neglected. The isoelectronic series of hydrogen is explored in the range Z = 1 ? 5 in both TDSE and perturbative approaches. Photoelectron angular distributions are obtained for photon energies of 1 keV and 3 keV for hydrogen, and photon energy of 25 keV for the hydrogenic ion B⁴⁺. Perturbative and TDSE calculations are compared.     

Uniform nanoparticles building Ce1?x Pr x O2?δ mesoarchitectures: structure, morphology, surface chemistry, and catalytic performance

The design of cell-based bioreactors for inorganic particles formation requires both a better understanding of the underlying processes and the identification of most suitable organisms. With this purpose, the process of Au³⁺ incorporation, intracellular reduction, and Au⁰ nanoparticle release in the culture medium was compared for four photosynthetic microorganisms, Klebsormidium flaccidum and Cosmarium impressulum green algae, Euglena gracilis euglenoid and Anabaena flos-aquae cyanobacteria. At low gold content, the two green algae show maintained photosynthetic activity and recovered particles (ca. 10?nm in size) are similar to internal colloids, indicating a full biological control over the whole process. In similar conditions, the euglenoid exhibits a rapid loss of biological activity, due to the absence of protective extracellular polysaccharide, but could grow again after an adaptation period. This results in a larger particle size dispersity but larger reduction yield. The cyanobacteria undergo rapid cell death, due to their prokaryotic nature, leading to high gold incorporation rate but poor control over released particle size. Similar observations can be made after addition of a larger gold salt concentration when all organisms rapidly die, suggesting that part of the process is not under biological control anymore but also involves extracellular chemical reactions. Overall, fruitful information on the whole biocrystallogenesis process is gained and most suitable species for further bioreactor design can be identified, i.e., green algae with external coating.     

Studies on Diels–Alder thermoresponsive networks based on ether–urethane bismaleimide functionalized poly(vinyl alcohol)

Thermoreversible networks obtained by the Diels–Alder cycloaddition reaction of poly(vinyl furfural) with urethane bismaleimides containing polyether chain were synthesized. The formation of the networks was confirmed by attenuated total reflectance in conjunction with Fourier transform infrared spectroscopy (ATR–FTIR). The materials thermal properties were investigated using differential scanning calorimetry (DSC) and a coupling of dynamic thermogravimetry with Fourier transform infrared spectroscopy and mass spectrometry (TG–FTIR–MS) for pyrolysis behaviour under nitrogen atmosphere. A thermal decomposition mechanism of the networks and poly(vinyl furfural) was discussed via evolved gas analysis. The thermoreversibility of the networks was demonstrated by the presence of the endothermic peak characteristic to the retrodienic process on the DSC heating curves and also the appearance of the exothermic peak, due to the dienic process, on the DSC cooling curve. The dynamic contact angle and free surface energy values of the networks were determined. Measures of the heterogeneity and roughness of the surfaces suggested that the surfaces of the networks’ films are more homogenous than the initial poly(vinyl furfural) surface. Dynamic water vapour sorption studies were conducted.     

Optimal control for linear discrete-time systems with Markov perturbations in Hilbert spaces

Email: vio{at}utgjiu.ro Received on September 12, 2007; Accepted on December 26, 2008 In this article, we discuss a quadratic control problem forlinear discrete-time systems with Markov perturbations in Hilbertspaces, which is linked to a discrete-time Riccati equationdefined on certain infinite-dimensional ordered Banach space.We prove that under stabilizability and stochastic uniform observabilityconditions, the Riccati equation has a unique, uniformly positive,bounded on N and stabilizing solution. Based on this result,we solve the proposed optimal control problem. An example illustratesthe theory.     

Mesoporous Pt-SiO2 and Pt-SiO2-Ta2O5 catalysts prepared using Pt colloids as templates.

Sol‐gel synthesis of silica and silica–tantalum oxide embedded platinum nanoparticles is carried out using Pt colloids as templates. These colloids are prepared by reduction with Na[AlEt₃H] and stabilized with different ligands (ammonium halide derivatives, non‐ionic surfactants with polyether chains, and 2‐hydroxy‐propionic acid). The aim of the present study is to prepare mesoporous silica embedded Pt colloids combining the “precursor concept” with the model of catalyst preparation using preformed spheres. Nanoparticles of Pt incorporated in high surface area mesoporous materials are formed after calcination. Further, it is observed that calcination of these catalysts causes partial aggregation and oxidation of the parent colloids, a process that is largely dependent on the nature of the stabilizing ligands. Several methods have been used for characterization of these materials: adsorption‐desorption isotherms at 77 K, H₂ chemisorption, X‐ray diffraction(XRD), ²⁹Si and ¹³C magic angle spinning (MAS) NMR, ammonia diffuse reflectance Fourier transform infrared spectroscopy (NH₃‐DRIFT), transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS). It is found that both metal oxide systems exhibit Brønsted acidity (weaker for silica and quite strong for silica–tantalum oxide). In addition, NH₃‐DRIFT experiments demonstrate the oxidative properties of the surface. Part of the adsorbed NH₄⁺ species is oxidized to N₂O. Testing these catalysts in the reduction of NO and NO₂ with isopentane under lean conditions indicate that the activity of these catalysts is indeed dependent on the size of the platinum particles, with those of size 8–10 nm demonstrating the best results. The support likely contributes to this effect, particularly after Ta incorporation into silica.