Electronic spectra of dithieno analogues of phenanthrene

The magnetic circular dichroism (MCD) spectra of some dithieno analogues of phenanthrene: benzo [2,1-b;3,4-b′] dithiophene (I) benzo [1,2-b;4,3-b′] dithiophene (II), benzo [1,2-c;3,4-c′] dithiophene (III) and benzo [1,2-b;3,4-b′] dithiophene (IV) are reported. For I–III the spectra corresponding to two different transition moment directions could be obtained from low-temperature linear dichroism spectra. The results compare well with theoretical energies, oscillator strengths, moment directions and MCD B-terms which were obtained from semi-empirical quantum mechanical calculations in the π-electron approximation.     

High-performance liquid chromatographic separation of gangliosides, combined with immunological detection and fast atom bombardment mass spectrometric characterization

A complete strategy for the isolation of individual mono- and disialogangliosides has been elaborated. We have used straight-phase silica gel chromatography or partitioning to obtain a crude ganglioside fraction. This fraction was then peracetylated and run through a second silica gel column. After anion-exchange chromatography the gangliosides were separated by straight-phase high-performance liquid chromatography with chloroform-methanol-water mixtures as eluting solvents. The method is suitable for preparative isolation of gangliosides and subsequent structural characterization by thin-layer chromatography-enzyme-linked immunosorbent assay, fast atom bombardment mass spectrometry and/or gas chromatography-mass spectrometry, which is demonstrated by several examples, including the separation of GalNAc-II3NeuAc-GgOse4Cer from GalNAc-isoII3NeuAc-GgOse4Cer.     

Supported Liquid Membrane Work-Up of Blood Plasma Samples Coupled On-Line to Liquid Chromatographic Determination of Basic Antidepressant Drugs

An automated sample pretreatment of human blood plasma for liquid chromatographic determination of three antidepressant drugs, dibenzepine; a tricyclic antidepressant (TCA), reboxetine; a selective noradrenaline reuptake inhibitor (SNRI) and fluvoxamine; a selective serotonin reuptake inhibitor (SSRI), based on supported liquid membrane (SLM) for unsurpassed sample clean-up and analyte enrichment, has been developed. The chromatograms after enrichment of plasma blank and aqueous blank are virtually indistinguishable. The entire analytical procedure revealed good linearity and low detection limits of 5, 15 and 20 ng mL^–1 for dibenzepine, reboxetine and fluvoxamine, respectively. No carry-over effects were noted. The repeatability of extraction at three concentrations in the range 40–150 ng mL^–1 for the three drugs was between ca. 3% and 7% as relative standard deviation. The reproducibility relative standard deviation during three different days (replacing the membrane each day) was not significantly higher.     

Determination of aliphatic amines in air by membrane enrichment directly coupled to a gas chromatograph

Summary A method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H₂SO₄, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL^–1 for C₁–C₆ amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m³ air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m³ (ca 0.2–0.5 ppt by volume) in air.     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

Retention in coupled capillary column supercritical fluid chromatography with lipids as model compounds

Summary We have investigated to which extent retention data, acquired on single capillary columns, can be used for predicting retention factors in a coupled column system. For this purpose we utilized a model mixture of 18 lipid components with widely different vapor pressures and polarities. The sample was chromatographed on two columns, SB-biphenyl-30 (70% methyl-30% biphenylpolysiloxane) and SB-cyanopropyl-50 (50% methyl-50% cyanopropylsiloxane). Experimental retention factors, acquired in coupled column systems with two columns connected in different order, were thus compared with values calculated from runs on each single column. The agreement between calculated and experimental values generally was better than 5% without any pressure drop correction.To study the possibility of predicting retention behavior in a wide pressure range from a limited number of experiments, we also investigated the relation between solute retention and mobile phase density. We found that all data could be fitted to second order equations, which gives the possibility to optimize the resolution with respect to pressure from a limited number of runs at different pressures.     

Medium energy proton induced fission in Tb,La and Ag

Coincidence studies with silicon surface barrier detectors have been used to determine fragment kinetic energies, angular correlations and fission cross sections in the fission of Ag,¹³⁹La,¹⁵⁹Tb and U nuclei induced by 600 MeV protons. Symmetric mass distributions are deduced for Ag and Tb, whereas La shows an indication of a stable asymmetric mass distribution. We find no indication of the Businaro-Gallone point. Fission-spallation competition calculations are used to deduce values of macroscopic fission barrier heights and nuclear level density parameter values at deformations corresponding to the saddle point shapes. We find macroscopic fission barriers lower than those predicted by macroscopic theories. The total kinetic energies at symmetric mass divisions follow closely the Viola prediction.