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1.
When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L−1 (r2s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L−1 and 0.50 mg L−1, respectively. The LOD and LOQ for trans-CA were 0.23 mg L−1 and 0.77 mg L−1, respectively. 相似文献
2.
A. Goldmann G. Rosina E. Bertel F. P. Netzer 《Zeitschrift für Physik B Condensed Matter》1989,73(4):479-487
We report electron spectroscopic studies of the Rh(111) surface, with the aim to obtain bulk band-structure information. We have measured normal photoemision using tunable synchrotron radiation in the range of photon energies between 11 eV and 55 eV, and angle-dependent photoemission along the LUX and LKL azimuths using the He resonance lines (=21.2 eV, 40.8 eV). To complement these data, we studied angleresolved secondary electron emission after excitation with electrons and photons. We derive parts of the one-electron energy dispersionE(k) along L, and determine the energies of several bulk critical points (in eV):E(>
7+/8+)=–2.75±0.10,E(>
8+=–0.85±0.10,E(>
7–=16.1±0.5,E(>
6–/>
8–)=20.5±0.5,E(X
7+)=–5.0±0.1,E(L
6+)=–5.6±0.5,E(L
6+/L
4++5+)=–2.65±0.10,E(L
6+)=9.0±0.5 eV. Our results are compared to several available band structure calculations. 相似文献
3.
Zusammenfassung Das Verbrennen von Mischungen der exothermen Systeme Al-NaF-NaNO3 und Al-CaF2-NaNO3 wurde durch Röntgenanalyse ergänzte DTA untersucht. Um den Einfluß des durch Dissoziation von NaNO3 gebildeten Sauerstoffs zu bestimmen wurden auch Mischungen, welche anstatt NaNO3 NaNO2 oder Na2O2 enthielten, geprüft.Zwei, bei 310° bzw. 850° einsetzende exotherme Reaktionen wurden in den Gemischen vom Typ Al-NaF-NaNO3 gefunden. Die erste ist der Dissoziation von NaNO3 zuzuschreiben, die zweite ist der Anwesenheit von Luft zuzuordnen.Beide exothermen Reaktionen wurden im System Al-CaF2-NaNO3 in Richtung höherer Temperaturen verschoben. Die Untersuchung der NaNO2- oder Na2O2-haltigen Gemische anstatt NaNO3 zeigte, daß die Dissoziation von NaNO3 den zum Verbrennen benötigten Sauerstoff liefert, andererseits würde letztere Reaktion sonst nur in begrenztem Ausmaß stattfinden.
Combustion of exothermic mixtures belonging to the system Al-NaF-NaNO3 and Al-CaF2-NaNO3 was investigated by DTA and X-ray analysis. In order to determine the influence of the oxygen generated by dissociation of NaNO3, the mixtures containing NaNO2 or Na2O2 instead of NaNO3 were also examined.Two exothermic reactions starting at 310° and 850° rsp. were found in the mixtures of the Al-NaF-NaNO3 type. The first is due to the dissociation of NaNO3 and the second proceeds independence of the availability of air.Both exothermic reactions were shifted to higher temperatures in the system Al-CaF2-NaNO3. Investigation of the mixtures containing NaNO2 or Na2O2 instead of NaNO3 has proved that the dissociation of NaNO3 supplies the oxygen required for combustion which should otherwise proceed only in a limited extent.
Résumé On a étudié, par ATD et par analyse aux rayons X, la combustion des mélanges exothermiques appartenant aux systèmes Al-NaF-NaNO3 et Al-CaF2-NaNO3. Afin de déterminer l'influence de l'oxygène engendré par la dissociation de NaNO3, on a étudié de même des mélanges contenant NaNO2 ou Na2O2 au lieu de NaNO3.On a trouvé, dans les mélanges du type Al-NaF-NaNO3, des réactions exothermiques à partir des temperatures respectives de 310° et 850°. La première est due à la dissociation de NaNO3 et la seconde dépend de l'air disponible.Dans le système Al-CaF2-NaNO3 les deux réactions sont déplacées vers les températures plus élevées. L'examen de mélanges contenant NaNO2 ou Na2O2 au lieu de NaNO3 à montré que c'est la dissociation de NaNO3 qui fournit l'oxygène nécessaire pour la combustion. Celleci n'aurait lieu, autrement, que d'une manière limitée.
, l-NaF-NaNO3 Al-CaF2-NaNO3. , NaNO3, , NaNO3, , NaNO2 Na2. , Al-NaF-NaNO3 , 310° 850°. , . Al-CaF2-NaNO3 . , NaNO2 Na2O2, , , , , .相似文献
4.
5.
Accreditation and Quality Assurance - 相似文献
6.
From the early precipitation-based techniques, introduced more than a century ago, to the latest development of enzymatic bio- and nano-sensor applications, the analysis of phytic acid and/or other inositol phosphates has never been a straightforward analytical task. Due to the biomedical importance, such as antinutritional, antioxidant and anticancer effects, several types of methodologies were investigated over the years to develop a reliable determination of these intriguing analytes in many types of biological samples; from various foodstuffs to living cell organisms. The main aim of the present work was to critically overview the development of the most relevant analytical principles, separation and detection methods that have been applied in order to overcome the difficulties with specific chemical properties of inositol phosphates, their interferences, absence of characteristic signal (e.g., absorbance), and strong binding interactions with (multivalent) metals and other biological molecules present in the sample matrix. A systematical and chronological review of the applied methodology and the detection system is given, ranging from the very beginnings of the classical gravimetric and titrimetric analysis, through the potentiometric titrations, chromatographic and electrophoretic separation techniques, to the use of spectroscopic methods and of the recently reported fluorescence and voltammetric bio- and nano-sensors. 相似文献
7.
Mitja Krnel Primož Koželj Stanislav Vrtnik Andreja Jelen Magdalena Wencka Peter Gille Janez Dolinšek 《无机化学与普通化学杂志》2020,646(14):1099-1104
We present the anisotropic electrical and thermal transport coefficients (electrical resistivity, magnetoresistance, thermoelectric power, thermal conductivity), the magnetic properties, the specific heat and the electronic density of states of a monocrystalline In3Ni2 intermetallic compound, representing a precious-metal-free (and noble-metal-free) intermetallic catalyst for the selective hydrogenation of α,β-unsaturated aldehydes. The investigated physical parameters were determined along three orthogonal crystal-symmetry directions of the trigonal structure, the twofold axis, the 3 axis and within the mirror plane. All the investigated tensorial and vectorial quantities show the same anisotropy, with the quantities being isotropic for the twofold direction and in the mirror plane, whereas there is small, though still significant anisotropy to the 3 direction. The In3Ni2 crystal conducts the electricity and heat somewhat less efficiently along the 3 direction than along the twofold direction and in the mirror plane, but the differences are not large, of about 20 %. In3Ni2 is a diamagnetic intermetallic compound, with a presumably simple Fermi surface and electrons as the majority charge carriers. 相似文献
8.
Giulia Festa Claudia Scatigno Francesco Armetta Maria Luisa Saladino Veronica Ciaramitaro Viviana Mollica Nardo Rosina Celeste Ponterio 《Molecules (Basel, Switzerland)》2022,27(1)
Spectral preprocessing data and chemometric tools are analytical methods widely applied in several scientific contexts i.e., in archaeometric applications. A systematic classification of natural powdered pigments of organic and inorganic nature through Principal Component Analysis with a multi-instruments spectroscopic study is presented here. The methodology allows the access to elementary and molecular unique benchmarks to guide and speed up the identification of an unknown pigment and its recipe. This study is conducted on a set of 48 powdered pigments and tested on a real-case sample from the wall painting in S. Maria Delle Palate di Tusa (Messina, Italy). Four spectroscopic techniques (X-ray Fluorescence, Raman, Attenuated Total Reflectance and Total Reflectance Infrared Spectroscopies) and six different spectrometers are tested to evaluate the impact of different setups. The novelty of the work is to use a systematic approach on this initial dataset using the entire spectroscopic energy range without any windows selection to solve problems linked with the manipulation of large analytes/materials to find an indistinct property of one or more spectral bands opening new frontiers in the dataset spectroscopic analyses. 相似文献
9.
Bellino Antonio Rosina 《Annali dell'Universita di Ferrara》1971,16(1):63-114
Riassunto In primo luogo viene giustificata la possibilità per un diametro autoconiugato di una quartica piana di essere asse di simmetria
obliqua (in particolare ortogonale) e dopo aver illustrato alcune proprietà sulla simmetria, vengono dati appropriati accorgimenti
onde procedere, con la ?piccola variazione?, alla costruzione effettiva delle quartiche piane (dei vari generi) dotate di
tutti i possibili assi di simmetria obliqua (in particolare ortogonale), dandone anche, caso per caso, la corrispondente equazione.
Nota II 相似文献
Résumé D'abord on justifie la possibilité, pour les diamètres auto-conjugués, d'être aussi des axes de symmetrie oblique (en particulier orthogonale) pour les quartiques planes et après avoir illustré plusieurs propriétés sur la symmetrie, on donne quelques avisements opportuns pour procéder après à la construction effective, avec la ?petite variation? des quartiques planes (de tous les genres) douées de tous les possibles axes de symmetrie oblique (en particulier, orthogonale), en donnant aussi, chaque cas à part, l'équation correspondante.
Nota II 相似文献
10.
This paper describes the use of Ag/Ag2S and Ag/AgI ion-selective electrodes by means of chemical pretreatment of a silver wire or tube for the determination of
cysteine (RSH) in batch and flow injection analysis (FIA).
Received December 15, 2000. Revision July 11, 2001. 相似文献