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1.
H. Falk R. Geerling B. Hattendorf K. Krengel-Rothensee K. P. Schmidt 《Analytical and bioanalytical chemistry》1997,359(4-5):352-356
An ICP-MS method for the determination of ultra-traces of 24 Elements (Li, Be, Mg, Al, Cr, Mn, Co, Zn, Cu, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Sn, Sb, Ba, Tl, Pb, Bi, U) at ng/L to μg/L levels in highly saline solutions (up to 30 g/L NaCl) was developed. Calculated to the salt content of the samples, limits of detection at the sub-μg/kg level were obtained. This allows the measurement of samples like sea water, or clinical samples like urine, serum and whole blood, with few or without sample preparation and a drastic improvement to the limits of detection. Compared to the determination in solutions of 1 g/L NaCl the limits of detection in the original sample were improved by one order of magnitude. Improvements in instrumental stability are achieved by the use of an additional gas, that is introduced to the aerosol stream and avoids salt deposition in the aerosol tube of the torch, the use of High Matrix Content (HMC) cones, that show no clogging even at NaCl-concentrations up to 50 g/L. With this setup the long term stability for measurements with changing matrix concentrations is < 10% without and < 5% with use of an internal standard for the individual samples. Cleaning up is necessary after 2 days of operation. The direct analysis of the Nearshore Seawater Reference Material NRC-CNRC CASS3 showed a good agreement with the certified and measured concentrations. Elements, that do not suffer from an isobaric overlap of matrix compounds can be determined clearly at ng/L levels. Measurement of different matrix concentrations showed, that acceptable results can be achieved with a single calibration for concentrations from 5 g/L NaCl to 30 g/L NaCl, though matrix matching shows the best results. 相似文献
2.
We discuss derivation‐like techniques for transforming one locally Hermitian partial ovoid of the Hermitian surface H(3,q2) into another one. These techniques correspond to replacing a regulus by its opposite in some naturally associated projective 3‐space PG(3,q) over a square root subfield. © 2006 Wiley Periodicals, Inc. J Combin Designs 15: 478–486, 2007 相似文献
3.
Benjamin Falk Santiago M. Vallinas James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2003,41(4):579-596
This article describes the development of optical pyrometry (OP) as a new analytical technique for the continuous monitoring of the progress of both free‐radical and cationic photopolymerizations. The method is rapid, reproducible, and very easy to implement. A temperature profile of a photopolymerization can be obtained. Preliminary studies have shown that the temperatures of some polymerizing monomers can easily reach temperatures in excess of 250 °C. The effects of the mass and reactivity of the monomer, light intensity, structures, and concentrations of the photoinitiators and monomers as well as the presence or absence of oxygen on various free‐radical and cationic photopolymerizations were examined with this method. Coupling of real‐time infrared spectroscopy with OP provides a convenient method for simultaneously monitoring both the chemical conversion and the temperature of a photopolymerization. This combined technique affords new insights into the effects of temperature‐induced autoacceleration on the course of photopolymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 579–596, 2003 相似文献
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5.
Summary N-Arylsubstituted ureas undergo exchange of the N-residue upon reaction with amines. Using kinetic measurements, investigation of product distribution, regioselectivity, catalysis, and substrate influences, it was shown that this reaction proceeds via a second order nucleophilic substitution at the urea carbonyl center. By means of semiempirical calculations using the MNDO method the alternative mechanism of fragmentation was investigated.
Zur Synthese N-substituierter Harnstoffe II: Nucleophile Substitution von Harnstoffen an der Carbonylgruppe
Zusammenfassung N-Arylsubstituierte Harnstoffe erleiden bei der Reaktion mit Aminen einen Austausch des N-Restes. Durch kinetische Messungen, Untersuchung der Produktverteilung, Regioselektivität, Katalyse und des Einflusses des Edukts konnte abgeleitet werden, daß es sich hiebei um eine nucleophile Substitution zweiter Ordnung am Carbonylzentrum des Harnstoffs handelt. Durch semiempirische Rechnungen mit Hilfe der MNDO Methode wurde der alternative Reaktionsmechanismus einer Fragmentierung untersucht.相似文献
6.
Heinz Falk Ernst Haslinger Thomas Schlederer 《Monatshefte für Chemie / Chemical Monthly》1979,110(6):1287-1294
The1H-NMR spin lattice relaxation times of aetiobiliverdin-IV- and biliverdindimethylester were determined using the inversion recovery technique. The relaxation times of protons attached to the terminal rings A and D are longer than those situated at the rings B and C which points to a higher mobility of rings A and D. Moreover these measurements allowed an independent assignment of the1H-NMR-signals of the methyl groups of biliverdindimethylester.
30. Mitt.:H. Falk undT. Schlederer, Ann. Chem., im Druck. 相似文献
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9.
Zhong-Le Huang Wolfgang Bensch Hubert Ebert 《Journal of solid state chemistry》2004,177(10):3245-3253
The effect of substitution of the anion Te by Se in non-stoichiometric Cr5Te8 has been investigated with respect to its crystal structure, magnetic properties, and electronic structure. The compounds Cr(1+x)Q2 (Q=Te, Se; Te:Se=7:1; (1+x)=1.234(6), 1.264(6), 1.300(7)) were synthesized at elevated temperatures followed by quenching the samples to room temperature. The crystal structures have been refined with X-ray powder diffraction data with the Rietveld method in the trigonal space group with lattice parameters a=3.8651(1)-3.8831(1) Å and c=5.9917(2)-6.0528(2) Å. The structure is related to the NiAs structure with full and deficient metal layers stacking alternatively along the c-axis. The irreversibility in the field-cooled/zero-field-cooled magnetization suggests that the substitution effects of one Te by one Se is strong enough to cause cluster-glass behavior, from ferromagnetic Cr5Te8 to cluster-glass Cr(1+x)Q2. Non-saturation magnetizations at 5.5 T and the magnetic relaxation results further support the existence of cluster-glass behavior. Accompanying SPR-KKR (spin-polarized relativistic Korringa-Kohn-Rostoker) band structure calculations strongly support the observation that the Cr(1) sites are preferentially occupied by Cr atoms and predict that these compounds are metallic. Results for the spin-resolved DOS and magnetic moments on each crystallographic sites are presented. 相似文献
10.
Zusammenfassung Ringschluß von -bzw. -Phenyl--ferrocenyl-buttersäure liefert die homoannular überbrückten Ketone (- bzw. -Phenyl--ketotetramethylen)-ferrocen (VI, VII, XIV). Die Ermittlung der Absolutkonfiguration dieser Ketone gelang durch Korrelation des Asymmetriezentrums der optisch aktiven -Phenyl--ferrocenyl-buttersäure (deren Absolutkonfiguration primär bestimmt wurde) mit der Konfiguration des planar asymmetrischen Anteils in den optisch aktiven Ketonen.Die erhaltenen Ergebnisse waren auch mit der früher für (+)-1,2-(-Ketotetramethylen)-ferrocen (I) auf unabhängigem Weg ermittelten Konfiguration in Einklang, wie durch Messung des optischen Circulardichroismus erwiesen werden konnte: die rechtsdrehenden Enantiomeren besitzen die (R), die linksdrehenden (S)-Konfiguration.
Mit 1 Abbildung
Über die Verwendung des Ausdruckes Ferrocen-Chiralität (bzw. Chiralitäts-Zentrum und Planar-Chiralität) vgl., Fußnote S. 266.
Vgl. hierzu die Fußnote auf S. 1066
3. Mitt. über Ferrocenasymmetrie, zugleich 24. Mitt. über Ferrocenderivate:H. Falk undK. Schlögl, Mh. Chem.96, 266 (1965). 相似文献
Ring closure of - and -phenyl--ferrocenylbutyric acid yielded the corresponding homoannularily bridged ketones, (- and -phenyl--ketotetramethylene)-ferrocene (VI, VII, XIV), respectively. The absolute configuration of these ketones could be established by correlation of the asymmetric center of the optically active -phenyl--ferrocenylbutyric acid (whose absolute configuration was determined previously) with the configuration of the planar asymmetric part in the optically active ketones.The results obtained support the configuration reported earlier for (+)-1,2-(-ketotetramethylene)-ferrocene (I) and established by an independent route. The configurations could also be supported by use of optical circular dichroism, i. e., the dextrorotatory enantiomers have the (R)-configuration, the laevorotatory the (S)-configuration.
Mit 1 Abbildung
Über die Verwendung des Ausdruckes Ferrocen-Chiralität (bzw. Chiralitäts-Zentrum und Planar-Chiralität) vgl., Fußnote S. 266.
Vgl. hierzu die Fußnote auf S. 1066
3. Mitt. über Ferrocenasymmetrie, zugleich 24. Mitt. über Ferrocenderivate:H. Falk undK. Schlögl, Mh. Chem.96, 266 (1965). 相似文献