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71.
Renata Wietecha Paweł Kościelniak Teresa Lech Tomasz Kielar 《Mikrochimica acta》2005,149(1-2):137-144
This study describes a simple, rapid and reliable method for simultaneous determination of selenium and arsenic in human hair by means of atomic fluorescence spectrometry combined with a hydride generation technique (HG-AFS). The procedure developed encompasses microwave digestion of a sample in the nitric acid environment only. The interferences caused by nitrous oxides are eliminated by removing a gas from above the digested solution with a stream of argon. The sample is then chemically treated in a flow-through hydride generation system and exposed to measurements in a double-channel atomic fluorescence spectrometer. The method permits determining both analytes in the linear range of 0.5–100µgL–1 with a detection limit equal to 0.2µgL–1, as well as with very good repeatability not exceeding 1% for Se and 2% for As. No mutual interferences from either of the analytes in the concentrations ranges matching the hair composition were found. The method was verified in terms of accuracy with the use of a reference material and then applied to the analysis of the natural samples of human hair. 相似文献
72.
Andrzej Maączyński Marian Góral Barbara Wiśniewska-Gocłowska Adam Skrzecz David Shaw 《Monatshefte für Chemie / Chemical Monthly》2003,134(5):633-653
Summary. The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility
of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is
used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane
in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental
data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature
range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental
data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the
data.
Corresponding author: E-mail: macz@ichf.edu.pl
Received August 5, 2002; accepted (revised) September 13, 2002
Published online March 13, 2003
RID="a"
ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70th birthday anniversary 相似文献
73.
Results of thermal and pyrolysis-GC/MS analyses of Na, Ca and Mg polyacrylates are presented. It was confirmed that the main decomposition reactions of the Na salt take place in the temperature range 420 – 470 and those of the other two polymers in the range 450–490. It was found that the solid residue after decomposition was the metal carbonate or oxide, while the volatile products consisted of H2, CO, CO2, saturated and unsaturated hydrocarbons (including cycloolefins and aromatic hydrocarbons) and aliphatic ketones. This suggests that the thermal decomposition of the metal polyacrylates proceeds via side-chain splitting and breaking of the main chain of the polymer, without retropolymerization.
Zusammenfassung Die Ergebnisse der Thermo- und Pyrolyse-GC/MS-analysen von Na-, Ca- und Mg-Polyacrylaten werden beschrieben. Es wurde bestÄtigt, dass die Hauptzersetzungsreaktionen des Natriumsalzes im Temperaturbereich von 420 bis 470, jene der anderen zwei Polymeren im Bereich von 450 bis 490 ablaufen. Es wurde nach der Zersetzung ein fester Rückstand von Metallkarbonat oder -oxid gefunden, wÄhrend die flüchtigen Produkte aus N2, CO, CO2, gesÄttigten und ungesÄttigten Kohlenwasserstoffen (darunter Zykloolefinen und aromatischen Kohlenwasserstoffen) und aliphatischen Ketonen bestanden. Dies lÄsst darauf schliessen, dass sich die thermische Zersetzung der Metallpolyacrylate über die Abspaltung der Seitenkette und der Spaltung der Hauptkette des Polymers ohne Retropolymerisation vollzieht.
Résumé On présente les résultats des analyses thermiques et des produits de décomposition pyrolytique par chromatographie en phase gazeuse et spectrométrie de masse (GC/MS) des polyacrylates de Na, Ca et Mg. On confirme que la réaction de décomposition principale du sel de sodium a lieu entre 420 et 470 et celle des deux autres polymères entre 450 et 490. On trouve que le résidu solide après décomposition est le carbonate ou l'oxyde du métal, tandis que les produits volatils consistent en N2, CO, CO2, en hydrocarbures saturés et non-saturés (y compris les cyclooléfines et hydrocarbures aromatiques) et en cétones aliphatiques. Cela permet de supposer que la décomposition thermique des polyacrylates métalliques s'effectue par coupure de la chaÎne latérale et par rupture de la chaÎne principale du polymère, sans rétropolymérisation.
-- -- Na, Ca Mg. , 420–470, — 450–490. , . H2, CO, CO2, , , . , .相似文献
74.
The influence of a partially filled conduction band on the magnetic properties of ferromagnetic semiconductors is studied within the framework of thes-f model. Allowing for magnon scattering to arbitrary order in the form of virtual electron- holecreation the magnon spectral density is derived, from which one gets magnon energies which are substantially renormalized by the presence of conduction electrons. In particular it is shown how the quasiparticle structure of the electronic excitation energies [4, 5] leads to scattering corrections in the magnon spectrum. These corrections are always negative and reduce the positive mean field part, which is proportional to the electron densityn. The calculated magnon spectrum is then used to determine the strikingn-dependence of the Curie-temperatureT
c
of Gd-doped EuO and EuS. 相似文献
75.
Ewa?Cholewa Ian?Burgess Julia?Kunze Jacek?LipkowskiEmail author 《Journal of Solid State Electrochemistry》2004,8(10):693-705
Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant
N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70th birthday and in recognition of his many contributions to electrochemistry. 相似文献
76.
Electrosorption of hydrogen into palladium-gold alloys 总被引:1,自引:0,他引:1
M. Łukaszewski K. Kuśmierczyk J. Kotowski H. Siwek A. Czerwiński 《Journal of Solid State Electrochemistry》2003,7(2):69-76
Hydrogen electrosorption into Pd-Au alloys has been studied in acidic solutions (1 M H2SO4) using cyclic voltammetry. Pd-Au electrodes with limited volume were prepared by electrochemical co-deposition. It was found
that the maximum H/(Pd+Au) ratios decrease monotonically with increasing gold content and reach zero at ca. 70 at% Au. Similarly
to the case of Pd limited volume electrodes, two peaks in the hydrogen region, corresponding to two types of sorbed hydrogen,
are observed on voltammograms for Pd-rich alloys. The hydrogen capacity, H/(Pd+Au), measured electrochemically, depends on
the sweep rate in the cyclic voltammetry experiments, which suggests that two different mechanisms for hydrogen desorption
from the Pd-Au alloy are possible. After a strong decrease of Pd concentration at the electrode surface, caused by long cyclic
polarization to sufficiently anodic potentials, the amount of absorbed hydrogen is still significant for alloys initially
rich in Pd. The results obtained from CO adsorption experiments suggest that only Pd atoms are active in the hydrogen absorption/desorption
process.
Electronic Publication 相似文献
77.
Differencies between the mechanism ofn-hexane and benzene adsorption on active carbon were investigated on the ground of kinetic measurements. As it has been stated, the kinetic measurements show fundamental differencies between the mechanism of adsorption in spite of analogy existing in the state of adsorption equilibrium. Within the range investigated, only the adsorption ofn-hexane follows the model of volume filling of micropores. Existence of those differencies is also confirmed by measurements of effective diffusion coefficient values as well as changes of activation energy of the diffusion—adsorption process.
Anwendung kinetischer Untersuchungen zur Interpretation des Adsorptionsverhaltens vonn-Hexan und Benzol an Aktivkohle
Zusammenfassung Mittels kinetischer Messungen untersuchte man die Unterschiede im Mechanismus des Adsorptionsverlaufes vonn-Hexan und Benzol an Aktivkohle. Man stellte fest, daß trotz der Analogie im Adsorptionsgleichgewichtszustand die kinetischen Messungen auf prinzipielle Unterschiede im Adsorptionsmechanismus hinweisen. Im untersuchten Bereich verläuft nur die Adsorption vonn-Hexane nach dem Modell der Mikroporenvolumenausfüllung. Die auftretenden Unterschiede wurden auch durch die Berechnungen der Werte der effektiven Diffusionskoeffizienten sowie Änderungen der Aktivierungsenergie des Diffusions-Adsorptionsprozesses bestätigt.相似文献
78.
Summary The method developed based on the determination of TC and TOC in the form of the total amount of CO2 requires application of the proper techniques for the final determination of CO2. The possibility of using a stream of carrier gas at a convenient flow-rate for desorbing quantitatively CO2 concentrated on a molecular sieve permits use of a wide variety of known analytical techniques for the final determination of CO2. Various methods were compared on the basis of both absolute and calibration measurements. The absolute methods chosen were gravimetric (classical or an automated version based on application of a gravimetric automat and automatic recording balance), thermogravimetric analysis and coulometry. The calibration methods included thermal conductivity, the flame-ionization detector (after conversion of CO2 into methane) and infrared absorption. Usefulness of the methods was evaluated on the basis of comparative statistical analysis of experimental data with respect to precision (Snedecor'sF-test and Bartlett'sU
2-test) and accuracy (Student'st-test).
Zusammenfassung Das entwickelte Verfahren zur Bestimmung des TC- und TOC-Gehaltes in Form der gesamten Menge CO2 erfordert die Anwendung geeigneter Analysentechniken zur Endbestimmung dieser Verbindung. Die Möglichkeit einer Desorption des am Molekularsieb angereicherten CO2 in einem Gasstrom mit geeignetem Durchfluß erlaubt zur Endbestimmung von CO2 die Anwendung einer Reihe verschiedener Analysenverfahren. Die Anwendbarkeit verschiedener, auf Absolutverfahren und auch auf relativen Messungen beruhender Methoden wurde vergleichend untersucht. Die folgenden Methoden zur CO2-Bestimmung wurden gewählt: die Gravimetrie (klassische oder automatisierte unter Einsatz eines Wägeautomaten und einer registrierenden Waage), die Thermogravimetrie und die Coulometrie. Von den relativen Methoden wurden die Thermokonduktometrie, der Flammenionisationsdetektor (nach Umsetzung von CO2 zu Methan) und das IR-Absorptionsmeßverfahren geprüft. Die Anwendbarkeit der Methoden wurde mit Hilfe statistischer Prüfverfahren beurteilt, wobei die Präzision (SnedecorsF-Test und BartlettsU 2-Test) und die Genauigkeit (Studentst-Test) der erhaltenen Analysenwerte verglichen wurden.相似文献
79.
Maciej Bujak Jacek Zaleski Victor Prezhdo Boris Uspenskiy 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(2):o76-o77
The title molecule, C11H12O3, is almost planar, with an average deviation of the C and O atoms from the least‐squares plane of 0.146 (4) Å. The geometry about the C=C bond is trans. The phenyl ring and –COOCH3 group are twisted with respect to the double bond by 9.3 (3) and 5.6 (5)°, respectively. The endocyclic angle at the junction of the propenoate group and the phenyl ring is decreased from 120° by 2.6 (2)°, whereas two neighbouring angles around the ring are increased by 2.3 (2) and 0.9 (2)°. This is probably associated with the charge‐transfer interaction of the phenyl ring and –COOCH3 group through the C=C double bond. The molecules are joined together through C—H?O hydrogen bonds between the methoxy and ester groups to form characteristic zigzag chains extended along the c axis. 相似文献
80.
Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air 总被引:3,自引:0,他引:3
Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed. 相似文献