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991.
Emil Völkert 《Accreditation and quality assurance》2004,9(4-5):237-238
Manufacturers support the concept of traceability. However, only a small number of the medically relevant measurands can be traced to the highest metrological order. In many cases, the measured substances are heterogeneous mixtures where traceability can be established only to either an international conventional reference measurement procedure or to a manufacturers own in-house reference system. The traceability concept needs to be seen in the context that the results of medical laboratories are not an aim per se, but are meant to provide useful medical information to clinicians, and that pre- and post-analytical steps may also contribute significantly to errors. There is a need for the further development of suitable reference measurement systems, but in view of the multitude of tasks and limited resources, priorities need to be set.Presented at BERM-9 – 9th International Symposium on Biological and Environmental Reference Materials, 15–19 June 2003, Berlin, Germany 相似文献
992.
This paper describes a new extraction tool for the determination of polycyclic aromatic hydrocarbons (PAHs) in soil and sediment samples, using dynamic microwave-assisted extraction combined with solid-phase extraction (DMAE-SPE). The critical variables for DMAE-SPE are investigated and optimized in an experimental design. The technique proved to be fast, accurate and able to yield quantitative extraction of PAHs from naturally contaminated sediment and soil samples. The set-up is fully automated and features monitored extraction, which facilitates rapid optimization of the method. In addition, only small quantities of solvent and sample are required. 相似文献
993.
Sven J. Cyvin Jon Brunvoll Björg N. Cyvin John L. Bergan E. Brendsdal 《Structural chemistry》1991,2(6):555-566
Hollow hexagons form a subclass of primitive coronoid systems. The macrocyclic aromatic hydrocarbon kekulene corresponds to a hollow hexagon. The hollow hexagons for given numbers of hexagonal units (h) were enumerated by computer aid, but also an analytical solution for the numbers of hollow hexagons was achieved. For the Kekulé structure counts (k) of a hollow hexagon a general formula is reported. Also the maximum and minimumK numbers are considered.This article is Part VI of the series Enumeration and Classification of Coronoid Hydrocarbons. For Part V, see ref. [36]. 相似文献
994.
[reactions: see text] Two complementary and efficient strategies have been developed for the regiospecific synthesis of unsymmetrical indolopyrrolocarbazoles (IPCs) mono-N-substituted with a pentacycle. A halogen in position 2 of the intermediate bisindolylmaleimides 3a-e allows a selective Mitsunobu coupling by exploiting the increased acidity of the 2-chloro-substituted indole nitrogen. It also promotes an easier cyclization of bisindolylmaleimides 4a-e and 7b-e to IPCs. Alkylation of the 2-unsubstituted indole-3-carboxamides 2a,b and further processing to the corresponding IPCs gives access to the opposite regioisomers. 相似文献
995.
A simple and inexpensive equipment for the optical resolution of enantiomers (and separation of diastereomers) on triacetylcellulose in ethanol at elevated pressure is described. It involves a closed circuit of solvent (pump—column—detector—pump) allowing a continuous chromatography up to 16 cycles without stopping the flow or handling fractions.This useful and versatile method permitting also the determination of enantiomeric purities is illustrated by several examples of centro-, axial- and planarchiral arenes and metallocenes.Herrn Prof. Dr.U. Schmidt, Stuttgart, zum 60. Geburtstag gewidmet. 相似文献
996.
Hyperfine structures of transitions in the a 3Πu ← X1Σg system of Na2 have been accurately measured by Doppler-free laser excitation spectroscopy in a collimated molecular beam. The hyperfine patterns are quantitatively explained and the reduced matrix elements of the magnetic dipole hf interaction determined from a least-squares fit to the measured line positions. 相似文献
997.
W. A. Schönfeldt P. H. Mokler D. H. H. Hoffmann A. Warczak 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,4(2):161-176
For 3.6 MeV/u Sm q+ projectiles a hump in the projectile (L l +L α) x-ray emission cross section is seen as a function of charge stateq for highq with 46≦q≦52 (closed incomingL shell). This hump is attributed to the Resonant electron Transfer from the Xe target atom with simultaneous Excitation of anL 3-shell electron to theM shell. The cross section for thisL 3-shell RTE process has values up to 2·10?19 cm2, which is seen in single spectra already. To verify the existence of theL-shell RTE process for the studied collision system, extensive calculations have been carried out. Especially theL 3-shell fluorescence yield for the radiative stabilization process in the highly-charged projectile has been considered. Our calculatedq-dependent cross sections for the RTE process support the given interpretation. 相似文献
998.
The nitration of 5‐amino‐1H‐tetrazole ( 1 ), 5‐amino‐1‐methyl‐1H‐tetrazole ( 3 ), and 5‐amino‐2‐methyl‐2H‐tetrazole ( 4 ) with HNO3 (100%) was undertaken, and the corresponding products 5‐(nitrimino)‐1H‐tetrazole ( 2 ), 1‐methyl‐5‐(nitrimino)‐1H‐tetrazole ( 5 ), and 2‐methyl‐5‐(nitramino)‐2H‐tetrazole ( 6 ) were characterized comprehensively using vibrational (IR and Raman) spectroscopy, multinuclear (1H, 13C, 14N, and 15N) NMR spectroscopy, mass spectrometry, and elemental analysis. The molecular structures in the crystalline state were determined by single‐crystal X‐ray diffraction. The thermodynamic properties and thermal behavior were investigated by using differential scanning calorimetry (DSC), and the heats of formation were determined by bomb calorimetric measurements. Compounds 2, 5 , and 6 were all found to be endothermic compounds. The thermal decompositions were investigated by gas‐phase IR spectroscopy as well as DSC experiments. The heats of explosion, the detonation pressures, and velocities were calculated with the software EXPLO5, whereby the calculated values are similar to those of common explosives such as TNT and RDX. In addition, the sensitivities were tested by BAM methods (drophammer and friction) and correlated to the calculated electrostatic potentials. The explosion performance of 5 was investigated by Koenen steel sleeve test, whereby a higher explosion power compared to RDX was reached. Finally, the long‐term stabilities at higher temperatures were tested by thermal safety calorimetry (FlexyTSC). X‐Ray crystallography of monoclinic 2 and 6 , and orthorhombic 5 was performed. 相似文献
999.
A simple intra- and inter-molecular potential for water molecules engaged in hydrogen bonding has been used in a one-dimensional approximation for a theoretical interpretation of the experimental correlation OH/OD versus OH in solid hydrates. The variation in the equilibrium OH(D) distance has also been considered. 相似文献
1000.
Comparison of the frequencies and half-widths of v1 in a variety of solvents shows that dispersion forces make a significant contribution to the effective intermolecular potential. Measurements of τv?1 and [ω2] in the CH3CN/CD3OD/CCl4 system demonstrates that long-range (hydrogen-bonding?) potentials significantly affect the relaxation rate. 相似文献