Selective serotonin reuptake inhibitors in sewage influents and effluents from Tromsø, Norway

The new membrane-enclosed silicone collector (MESCO) was, in two different configurations with respect to the thickness of low-density polyethylene membrane used, subject to serial batch extraction tests to obtain (preliminary) sampling rates for estimating water concentrations of selected chlorinated organic compounds and polycyclic aromatic hydrocarbons. This rapid calibration procedure is simple to implement compared to experiments in a flow-through apparatus and yielded reasonable sampling rates in the range of 50 microL-2 mL per hour for the compounds tested. The new MESCO formats were also exposed for 28 days in the polluted creek to test their field performance. For priority contaminants of special interest, alpha-hexachlorocyclohexane and hexachlorobenzene, the time-weighted average concentrations derived from the freshly calibrated sampling devices agree well with those obtained by conventional water analysis of spot samples.     

Experimental passive self-tuning behavior of a beam resonator with sliding proof mass

A passively self-tuning resonator configuration is presented in this study. Three different prototype beam–mass systems were built and tested and all successfully displayed passive self-tuning behavior when driven by vibrations at frequencies ranging from 45 to 140 Hz and accelerations ranging from 0.007 to 2g. All three systems were able to achieve tuning within their operating regime when driven at a single frequency, as well as maintain a tuned condition as frequency was stepped up or down, demonstrating a bandwidth between 6 and 40 Hz. One application of such a passively self-tuning system is in vibration energy harvesting, where it is critical for performance that the harvester device resonance frequency matches the input vibration frequency, yet the input frequency may change over time and is not known a priori. The self-tuning resonator demonstrated in this paper can enable the energy harvesting system to adjust to the varying input frequencies and thereby increase the energy harvested over time.     

Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME)--practical considerations in the three-phase mode

In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8-79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1-7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4-3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenylmethylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature.     

Stable pentacoordinate carbocations: structure and bonding

We report that only elements more electropositive than carbon (Group 13, 14, and Be) form stable symmetrical HnE--CH3--EHn + structures (E=Group 1, 2, 13, or 14 element) with a planar CH3 group symmetrically bonded to two EHn moieties, in analogy with prototypical SN2 transition structures. Analysis of the bonding situation of these pentacoordinate carbon molecules was studied by means of an energy decomposition analysis (EDA) of the interaction energy. This shows that HnE--CH3--EHn + molecules can be viewed as being composed of one CH3 group that is sigma-covalently bonded to two EHn groups forming a three-center, two-electron bond.     

Percolation in layered media — A conductivity approach

Long square-lattice and cubic-lattice samples consisting of many layers are simulated. Within each layer, the concentration of permeable bonds is constant whereas each layer has a different concentration chosen randomly from the interval between the percolation threshold and unit concentration. The conductivity of the random resistor network corresponding to this percolation model is calculated, both parallel and perpendicular to the layers, in both two and three dimensions. For the conductivity parallel to the layers, an effective medium calculation comes within 10% of the true conductivity. For the conductivity perpendicular to the layers, percolation theory is necessary.List of Symbols G Total Conductivity in units of the conductivity of one bond - L Length of sample in units of the length of one bond - n Width of sample in units of the length of one bond - N Number of layers - p Probability that a bond conduct - p _c Percolation threshold - R Resistivity in units of the resistivity of one bond - t Percolation conductivity exponent - v Percolation correlation length exponent - Correlation length in units of the length of one bond     

Parallel electromembrane extraction in the 96-well format

The repeatability and extraction recoveries of parallel electromembrane extraction (Pa-EME) was thoroughly investigated in the present project. Amitriptyline, fluoxetine, and haloperidol were isolated from eight samples of pure water, undiluted human plasma, and undiluted human urine, respectively; in total 24 samples were processed in parallel. The repeatability was found to be independent of the different sample matrices (pure water samples, human plasma, and water) processed in parallel, although the respective samples contained different matrix components. In another experiment seven of the 24 wells were perforated. Even though the perforation caused the total current level in the Pa-EME setup to increase, the intact circuits were unaffected by the collapse in seven of the circuits. In another approach, exhaustive extraction of amitriptyline, fluoxetine, and haloperidol was demonstrated from pure water samples. Amitriptyline and haloperidol were also isolated exhaustively from undiluted human plasma samples; the extraction recovery of fluoxetine from undiluted human plasma was 81%. Finally, the sample throughput was increased with the Pa-EME configuration. The extraction recoveries were investigated by processing 1, 8, 68, or 96 samples in parallel in 10 min; neither the extraction recoveries nor the repeatability was affected by the total numbers of samples. Eventually, the Pa-EME was combined with ultra performance liquid chromatography (UPLC) to combine high-throughput sample preparation with high-throughput analytical instrumentation. The aim of the present investigation was to demonstrate the potential of electromembrane extraction as a high throughput sample preparation platform; and hopefully to increase the interest for EME in the bioanalytical field to solve exisiting and novel analytical challenges.     

Microextraction across supported liquid membranes forced by pH gradients and electrical fields

The present work has for the first time compared extraction of basic analytes across a supported liquid membrane (SLM) based on (1) passive diffusion in a pH gradient sustained over the SLM and (2) electrokinetic migration in an electrical field sustained over the SLM. For the passive diffusion experiments, performed as liquid-phase microextraction (LPME), five basic drugs were extracted under strong agitation from alkaline samples (10mM NaOH), through 2-nitrophenyl octylether immobilized in the pores of a porous hollow fibre of polypropylene (SLM), and into 25 microl of 10mM HCl as the acceptor solution. The experiments based on electrokinetic migration, performed as electro membrane isolation (EMI), were conducted under strong agitation from acidic samples (10mM HCl), through the same SLM as in LPME, and into 25 microl of 10mM HCl as the acceptor solution. Whereas LPME relied on diffusion and to some extent also convection as the principal mechanisms of mass transfer, mass transfer in EMI also included a strong contribution from electrokinetic migration. Thus, extraction kinetics was improved by a factor between 6 and 17 utilizing EMI instead of LPME. This major difference in terms of speed was especially pronounced from small sample volumes (150 microl), and suggest that EMI may be a very interesting future concept for miniaturized sample preparation. In addition to improved extraction kinetics, extraction rates were strongly compound dependent in EMI, opening the possibility to control the extraction selectivity by the extraction time.     

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