Denuder sampling system for the determination of gaseous and particle-bound organic health hazardous substances

A novel denuder system for the determination of airborne hazardous organic substances is presented. A special wall coating technique allows to reuse the denuder after a regeneration procedure. The denuder system has been designed for workplace air monitoring and can be used in combination with filters and back-up adsorbents to distinguish between the gaseous and the particle-bound phase of a compound. The use of dynamically generated test gases has been enabled reliable determinations of uptake rates and adsorption capacities as well as desorption efficiencies at different conditions. The penetration of particulate matter through the denuder has been examined.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

CYCLCROP indirect 13C mapping for long-time and chemical-shift selective diffusion measurements in complex hydrocarbon systems

Cyclic cross-polarization from a proton magnetization to ¹³C and from there back to proton coherences permits the indirect, ¹³C chemical shift selective detection of hydrocarbon compounds in the proton NMR channel. This excitation technique can be combined with elements of one-, two- or three-dimensional magnetic resonance imaging permitting the measurement of time-resolved spatial distributions of hydrocarbon components. Beginning this sort of CYCLCROP mapping experiment with a non-equilibrium distribution of the constituents in the system allows one to study the time evolution of the concentrations of all components that can be identified by characteristic ¹³C resonance lines. As applications, studies of ingress, mixing, gel formation, transport and metabolism in living plants, long-time inter- and self-diffusion in complex hydrocarbon systems are suggested. As a test experiment, the diffusion of methanol in swollen polymethylmethacrylate was examined.     

Kinetically stable complexes in water: the role of hydration and hydrophobicity

We describe here the synthesis and characterization of a molecular receptor that forms kinetically and thermodynamically stable host-guest complexes in water. This cavitand-based host is composed of a preorganized aromatic pocket whose rim is decorated with four negatively charged carboxylate groups. (1)H NMR and isothermal titration calorimetry have been used to characterize the behavior of the resulting complexes in response to changes in pH, buffer identity, and salt concentration and in the presence of sodium dodecyl sulfate micelles.     

Strategic views of accreditation

This paper summarises the experience we gained while going through an accreditation process in accordance with the requirements of ISO/IEC 17025 Standard. We propose in this paper an initial path finding study stage to evaluate the laboratory's predisposition for, and the benefits of, accreditation. We also present a conceptual framework as part of the path finding study stage to identify and classify different groups of activities in a laboratory into separate business domains. The objective of the study is to assess, for each business domain, the approach, the benefits, costs and implications of working with a systematic QA and then design a priori appropriate working systems tailored to the real needs of each business. Such a study should naturally lead to an appropriate definition of accreditation scope.

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Vibrational energy storage in high pressure mixtures of diatomic molecules

CO/N₂, CO/Ar/O₂, and CO/N₂/O₂ gas mixtures are optically pumped using a continuous wave CO laser. Carbon monoxide molecules absorb the laser radiation and transfer energy to nitrogen and oxygen by vibration–vibration energy exchange. Infrared emission and spontaneous Raman spectroscopy are used for diagnostics of optically pumped gases. The experiments demonstrate that strong vibrational disequilibrium can be sustained in diatomic gas mixtures at pressures up to 1 atm, with only a few Watts laser power available. At these conditions, measured first level vibrational temperatures of diatomic species are in the range T_V=1900–2300 K for N₂, T_V=2600–3800 K for CO, and T_V=2200–2800 K for O₂. The translational–rotational temperature of the gases does not exceed T=700 K. Line-of-sight averaged CO vibrational level populations up to v=40 are inferred from infrared emission spectra. Vibrational level populations of CO (v=0–8), N₂ (v=0–4), and O₂ (v=0–8) near the axis of the focused CO laser beam are inferred from the Raman spectra of these species. The results demonstrate a possibility of sustaining stable nonequilibrium plasmas in atmospheric pressure air seeded with a few percent of carbon monoxide. The obtained experimental data are compared with modeling calculations that incorporate both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, showing reasonably good agreement.     

Dysprosium Complexes and Their Micelles as Potential Bimodal Agents for Magnetic Resonance and Optical Imaging

Six diethylene triamine pentaacetic acid (DTPA) bisamide derivatives functionalized with p‐toluidine (DTPA‐BTolA), 6‐aminocoumarin (DTPA‐BCoumA), 1‐naphthalene methylamine (DTPA‐BNaphA), 4‐ethynylaniline (DTPA‐BEthA), p‐dodecylaniline (DTPA‐BC₁₂PheA) and p‐tetradecyl‐aniline (DTPA‐BC₁₄PheA) were coordinated to dysprosium(III) and the magnetic and optical properties of the complexes were examined in detail. The complexes consisting of amphiphilic ligands (DTPA‐BC₁₂PheA and DTPA‐BC₁₄PheA) were further assembled into mixed micelles. Upon excitation into the ligand levels, the complexes display characteristic Dy^III emission with quantum yields of 0.3–0.5 % despite the presence of one water molecule in the first coordination sphere. A deeper insight into the energy‐transfer processes has been obtained by studying the photophysical properties of the corresponding Gd^III complexes. Since the luminescence quenching effect is decreased by the intervention of non‐ionic surfactant, quantum yields up to 1 % are obtained for the micelles. The transverse relaxivity r₂ per Dy^III ion at 500 MHz and 310 K reaches a maximum value of 27.4 s^?1 mM ^?1 for Dy‐DTPA‐BEthA and 36.0 s^?1 mM ^?1 for the Dy‐DTPA‐BC₁₂PheA assemblies compared with a value of 0.8 s^?1 mM ^?1 for Dy‐DTPA. The efficient T₂ relaxation, especially at high magnetic field strengths, is sustained by the high magnetic moment of the dysprosium ion, the coordination of water molecules with slow water exchange kinetics and long rotational correlation times. These findings open the way to the further development of bimodal optical and magnetic resonance imaging probes starting from single lanthanide compounds.     

Determination of benzothiazole in untreated wastewater using polar-phase stir bar sorptive extraction and gas chromatography-mass spectrometry

Stir bar sorptive extraction (SBSE) was applied to extract benzothiazole (BT) from untreated wastewater using a novel polyacrylate (PA)-coated stir bar (PA Twister^®). After extraction, BT was desorbed in a thermal desorption system (TDS) and analysed by GC–MS (gas chromatography–mass spectrometry). The sample contained 30% (w/w) NaCl, the sample temperature was 30 °C and the extraction time was 240 min. Since no filtering or clean-up steps or solvents were necessary SBSE clearly performs better than all previously used extractions techniques for analysing BT in untreated wastewater in terms of easy use, sample throughput and analytical costs. In addition, matrix effects were small. The calibration curve resulting from the standard addition method was linear with a value of the stability index (R²) of 0.999 (n = 3). A good inter-day repeatability of the method was observed with a relative standard deviation (RSD) of 9.8% (n = 6). A low limit of detection (LOD) of 0.256 μg L⁻¹ was achieved using only a small sample volume of 18 mL. Small sample volumes significantly reduce sample transport costs. The concentration of BT in untreated wastewater was determined to be 1.04 μg L⁻¹.