Wasseruntersuchung

Ohne Zusammenfassung     

Einen Annarat zur selbstt?tigen Reinigung von Laboratoriumsger?ten

Ohne Zusammenfassung     

Zur Kenntnis der Vorgänge,welche in einem Kaolin bei allmählich ansteigender Erhitzung in Gegenwart von Luft und anderen Fremdgasen stattfinden

Ohne Zusammenfassung 121. Mitteilung H. Kappel und G. F. Hüttig, Kolloid-Z.91, 117 (1940); 119. Mitteilung G. F. Hüttig und H. Kappel, Angew. Chem.53, 57 (1940). Wir sind der Deutschen Forschungsgemeinschaft und dem Reichsamt für Wirtschaftsausbau zu gro?em Danke verpflichtet, da? sie uns durch ihre Unterstützung erm?glichten, die vorliegenden Untersuchungen zum Abschlu? zu bringen.     

Monitoring apple flavor by use of quartz microbalances

"Electronic noses", i.e. arrays of differently coated quartz microbalances (QMB), have been used for selective detection of, and discrimination between, volatile organic compounds (VOC) formed during the post-harvest ripening of apples. The flavor components to be differentiated are chemically rather similar carbonyl compounds, chiefly aldehydes and esters. Because their relative ratios change during the post-harvest ripening period, appropriately selected sensor-active layers lead to characteristic patterns of the sensor responses which can be analyzed via pattern-recognition methods. This enables qualitative and quantitative identification of individual components whereby the post-harvest ripening of apples and other fruits can be monitored. Different kinds of apple differ in type and concentration of individual carbonyl compounds.     

Ions generated from uranyl nitrate solutions by electrospray ionization (ESI) and detected with fourier transform ion-cyclotron resonance (FT-ICR) mass spectrometry

Electrospray ionization (ESI) of uranyl nitrate solutions generates a wide variety of positively and negatively charged ions, including complex adducts of uranyl ions with methoxy, hydroxy, and nitrate ligands. In the positive ion mode, ions detected by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry are sensitive to instrumental tuning parameters such as quadrupole operating frequency and trapping time. Positive ions correspond to oligomeric uranyl nitrate species that can be characterized as having a general formula of [(UO(2))(n)(A)(m)(CH(3)OH)(s)](+) or [(UO(2))(n)(O)(A)(m)(CH(3)OH)(s)](+) with n = 1-4, m = 1-7, s = 0 or 1, and A = OH, NO(3), CH(3)O or a combination of these, although the formation of NO(3)-containing species is preferred. In the negative ion mode, complexes of the form [(UO(2))(NO(3))(m)](-) (m = 1-3) are detected, although the formation of the oxo-containing ions [(UO(2))(O)(n)(NO(3))(m)](-) (n = 1-2, m = 1-2) and the hydroxy-containing ions [(UO(2))(OH)(n)(NO(3))(m)](-) (n = 1-2, m = 0-1) are also observed. The extent of coordinative unsaturation of both positive and negative ions can be determined by ligand association/exchange and H/D exchange experiments using D(2)O and CD(3)OD as neutral reaction partners in the gas-phase. Positive ions are of varying stability and reactivity and may fragment extensively upon collision with D(2)O, CD(3)OD and N(2) in sustained off-resonance irradiation/collision-induced dissociation (SORI-CID) experiments. Electron-transfer reactions, presumably occurring during electrospray ionization but also in SORI-CID, can result in reduction of U(VI) to U(V) and perhaps even U(IV).     

Hydroxyl radical reactions with halogenated ethanols in aqueous solution: Kinetics and thermochemistry

Laser flash photolysis combined with competition kinetics with SCN^? as the reference substance has been used to determine the rate constants of OH radicals with three fluorinated and three chlorinated ethanols in water as a function of temperature. The following Arrhenius expressions have been obtained for the reactions of OH radicals with (1) 2‐fluoroethanol, k₁(T) = (5.7 ± 0.8) × 10¹¹ exp((?2047 ± 1202)/T) M^?1 s^?1, (2) 2,2‐difluoroethanol, k₂(T) = (4.5 ± 0.5) × 10⁹ exp((?855 ± 796)/T) M^?1 s^?1, (3) 2,2,2‐trifluoroethanol, k₃(T) = (2.0 ± 0.1) × 10¹¹ exp((?2400 ± 790)/T) M^?1 s^?1, (4) 2‐chloroethanol, k₄(T) = (3.0 ± 0.2) × 10¹⁰ exp((?1067 ± 440)/T) M^?1 s^?1, (5) 2, 2‐dichloroethanol, k₅(T) = (2.1 ± 0.2) × 10¹⁰ exp((?1179 ± 517)/T) M^?1 s^?1, and (6) 2,2,2‐trichloroethanol, k₆(T) = (1.6 ± 0.1) × 10¹⁰ exp((?1237 ± 550)/T) M^?1 s^?1. All experiments were carried out at temperatures between 288 and 328 K and at pH = 5.5–6.5. This set of compounds has been chosen for a detailed study because of their possible environmental impact as alternatives to chlorofluorocarbon and hydrogen‐containing chlorofluorocarbon compounds in the case of the fluorinated alcohols and due to the demonstrated toxicity when chlorinated alcohols are considered. The observed rate constants and derived activation energies of the reactions are correlated with the corresponding bond dissociation energy (BDE) and ionization potential (IP), where the BDEs and IPs of the chlorinated ethanols have been calculated using quantum mechanical calculations. The errors stated in this study are statistical errors for a confidence interval of 95%. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 174–188, 2008     

Excitation Dynamics in High-precision Two-photon Spectroscopy

High-precision two-photon spectroscopy of hydrogen and hydrogenlike systems allows for stringent tests of bound state QED and provides a laboratory tool to probe a possible drift of fundamental constants. On the current level of accuracy in determining the hydrogen 1S-2S absolute frequency , it is crucial to take into account the time-dependent nature of the excitation process, in order to correctly describe the experimental observations. In particular, the ionization of the excited state by absorption of a single additional laser photon restricts the interaction time in the spectroscopy experiment and prevents the system from evolving into a populated steady state.     

Rates of rotational diffusion and Heisenberg spin exchange as obtained from CW ESR and ESR tomographic experiments on model systems and human skin

The purpose of the present paper is to describe possibilities and limitations for the determination of the rates of rotational diffusion and Heisenberg spin exchange, obtained from continuous-wave electron spin resonance (cw ESR) and ESR tomographic experiments. Model systems including nitroxides as paramagnetic reporter molecules have been examined in order to verify data, which have been obtained from cw ESR and ESR tomography. This has been done with particular emphasis on checking the influence of concentration, temperature, and viscosity on the spectral-spatial properties. These findings have been applied to the evaluation of penetration and permeation studies on human skin. The extracted full spectral information from ESR tomography allows the determination of the above mentioned dynamic parameters for model systems of definite geometry and for samples of human skin. It has been found that the signal-to-noise ratio is critical for all discussed applications.