Laser-excited ionic fluorescence spectrometry of rare-earth elements in the inductively-coupled plasma

A pulsed tunable dye laser pumped with an excimer laser is used to excite ionic fluorescence of the rare earth elements in the inductively-coupled plasma. Because several fluorescence lines were observed after laser excitation, it was possible to draw partial energy-level diagrams for most of the rare earths. Non-resonance fluorescence lines were used for all measurements in order to minimize spectral interferences. Detection limits at given excitation wavelengths are reported for each element. Laser-excited ionic fluorescence eliminates the problem of spectral interferences which has been associated with the determination of the rare earths by atomic emission spectrometry in the inductively-coupled plasma.     

Simultaneous determination of ondansetron and tropisetron in human plasma using HPLC with UV detection

A rapid and sensitive HPLC method for the simultaneous quantitation of ondansetron and tropisetron, two serotonin (5-HT) receptor antagonists frequently used in treatment and prevention of nausea and emesis, is described. The procedure involves liquid-liquid extraction of human plasma with dichloromethane coupled with reversed-phase HPLC and UV detection. The lower limits of quantification (LOQ) were 0.62 ng/mL for ondansetron and 1.25 ng/mL or tropisetron. Intra- and inter-assay coefficients of variation ranged from 1.5 to 7.5% and 5.3 to 13.7%, respectively. The sensitivity and precision were sufficient for determination of plasma concentrations after therapeutic administration of both drugs and the method can be used for the estimation of pharmacokinetic parameters.     

Tuning PtII-Based Donor–Acceptor Systems through Ligand Design: Effects on Frontier Orbitals,Redox Potentials,UV/Vis/NIR Absorptions,Electrochromism, and Photocatalysis

Asymmetric platinum donor–acceptor complexes [(pimp)Pt(Q²⁻)] are presented in this work, in which pimp=[(2,4,6-trimethylphenylimino)methyl]pyridine and Q²⁻=catecholate-type donor ligands. The properties of the complexes are evaluated as a function of the donor ligands, and correlations are drawn among electrochemical, optical, and theoretical data. Special focus has been put on the spectroelectrochemical investigation of the complexes featuring sulfonyl-substituted phenylendiamide ligands, which show redox-induced linkage isomerism upon oxidation. Time-dependent density functional theory (TD-DFT) as well as electron flux density analysis have been employed to rationalize the optical spectra of the complexes and their reactivity. Compound 1 ([(pimp)Pt(Q²⁻)] with Q²⁻=3,5-di-tert-butylcatecholate) was shown to be an efficient photosensitizer for molecular oxygen and was subsequently employed in photochemical cross-dehydrogenative coupling (CDC) reactions. The results thus display new avenues for donor–acceptor systems, including their role as photocatalysts for organic transformations, and the possibility to introduce redox-induced linkage isomerism in these compounds through the use of sulfonamide substituents on the donor ligands.     

Probing Electronic Symmetry Reduction during Charge Migration via Time-Resolved X-Ray Diffraction

The present work focuses on probing ultrafast charge migration after symmetry-breaking excitation using ultrashort laser pulses. LiCN is chosen as prototypical system because it can be oriented in the laboratory frame and it possesses optically-accessible charge transfer states at low energies. The charge migration is simulated within the hybrid time-dependent density functional theory/configuration interaction framework. Time-resolved electronic current densities and simulated time-resolved x-ray diffraction signals are used to unravel the mechanism of charge migration. Our simulations demonstrate that specific choices of laser polarization lead to a control over the symmetry of the induced charge migration. Moreover, time-resolved x-ray diffraction signals are shown to encode transient symmetry reduction at intermediate times.     

Modeling of Wormhole Growth in Cold Production

Cold production is a non-thermal process in which sand is intentionally produced with the oil in order to enhance oil recovery. Two experiments were performed to investigate the effect of producing large quantities of sand on the overall permeability of a formation. A large high porosity channel (wormhole) was observed in both experiments. A model of wormhole growth was successfully tested in two sand production experiments simulating the growth of a wormhole from a perforation in a vertical well. The produced volumes of oil, sand and gas, the pressure distribution along the pack and the final length of the wormholes were well predicted. The two sand packs had significantly different cohesive strengths. The strength of the sand did not have a significant effect on the growth of the wormholes. The formation of tensile failure bands at the wormhole surface, as observed in the experiments, may weaken the sand and allow it to be fluidized more easily. This weakening effect would explain the lower pressure gradients calculated at the surface of the wormhole while it developed compared to the critical pressure gradient for sand production predicted by Bratli and Risnes (1981).