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21.
Halina Polkowska-Motrenko Rajmund S. Dybczyński Ewelina Chajduk 《Accreditation and quality assurance》2010,15(4):245-250
This paper presents the work done by the Institute of Nuclear Chemistry and Technology (INCT), Warsaw on a procedure of the
certification of matrix reference materials (CRMs) for inorganic trace analysis. The INCT has been involved in preparation
and certification of that type of CRMs since 1986 till now. The certification of CRMs is performed on the basis of statistical
evaluation of the data obtained from the worldwide interlaboratory comparison. The initially adopted certification procedure
has been developed, and the final shape is presented and discussed. The modifications are connected with the new demands of
the international standards. The results of analysis of candidate CRMs obtained by the potentially primary procedures based
on radiochemical neutron activation analysis (RNAA) and results of analysis of CRM accompanying candidate RMs are applied
in the certification process for quality assurance purpose. 相似文献
22.
Stanis?aw Krompiec Mateusz Penkala Ewelina Kowalska Robert Penczek Piotr Bujak Witold Danikiewicz Grzegorz Spólnik Andrzej Kita Iwona Grudzka 《Monatshefte für Chemie / Chemical Monthly》2011,33(7):1241-1247
Abstract
Ru-catalyzed synthesis of mixed alkyl–alkyl acetals via addition of primary alcohols to allyl ethers has been extended to include long-chain and/or functionalized substrates. The catalytic systems for these reactions were generated from RuCl2(PPh3)3 and [RuCl2(1,5-COD)]x and phosphines [PPh3 or P(p-chlorophenyl)3] or SbPh3. Of particular importance is the almost quantitative elimination of transacetalization. The addition proceeds through allyl complexes, not via isomerization of allyl ethers––subsequent addition of ROH to vinyl ethers. 相似文献23.
The room temperature and cryogenic terahertz (THz) spectra (10-95 cm(-1)) of l-tartaric acid and dl-tartaric acid were investigated. At 293 K, the l-tartaric acid spectrum showed four absorption features at 36.4, 61.6, 78.7, and 87.3 cm(-1) in the experimental spectrum. Once cooled to 78 K, these features narrowed and shifted to 35.9, 63.4, 81.1, and 90.1 cm(-1). The THz spectrum of dl-tartaric acid is significantly different, containing only a single absorption at 79.9 cm(-1) at room temperature, which shifts to 82.9 cm(-1) at 78 K. Solid-state density functional theory calculations [B3LYP/6-311G(2d,2p)] were performed to simulate the crystalline structure of both molecular solids and to assign the observed spectral features to specific atomic motions. The THz spectrum of l-tartaric acid is particularly interesting in that it contains a theoretically unaccounted for spectral feature that may arise from second-order phonon processes and also exhibits an anomalous red-shifting absorption feature with cooling that is shown to originate from negative thermal expansion of the crystal. 相似文献
24.
Terahertz spectroscopy provides a noninvasive and nondestructive method for detecting and identifying concealed explosives. In this work, the room-temperature and cryogenic terahertz spectra of two common improvised explosive oxidizers, namely, potassium nitrate (KN) and ammonium nitrate (AN), are presented, along with detailed solid-state density functional theory (DFT) analyses of the crystalline structures and spectral features. At both 294 and 78 K, KN exhibits two terahertz absorption features below 100 cm(-1) that have been assigned through DFT simulations to arise from hindered nitrate rotations in the KN-II crystalline polymorph. The terahertz spectrum of AN exhibits a pronounced temperature dependence. The 294 K spectrum is free of any absorptions, whereas the 78 K spectrum consists of several narrow and intense peaks. The origin of this large difference is the polymorphic transition that occurs during cooling of AN, where room-temperature AN-IV is converted to AN-V at 255 K. The 78 K terahertz spectrum of AN is assigned here to various ion rotations and translations in the AN-V polymorph lattice. The analysis of the room-temperature AN-IV terahertz spectrum proved to be more complicated. The solid-state DFT simulations predicted that the room-temperature crystal structure of AN is not very well described using the standard Pmmn space-group symmetry as previously believed. The AN-IV polymorph actually belongs to the Pmn2(1) space group, and the perceived Pmmn symmetry results from vibrational averaging through nitrate rotations. This newly observed Pmn2(1) crystal symmetry for room-temperature AN is the reason for the absence of absorption features in the 294 K terahertz spectrum of AN and provides new insight into the polymorphic transitions of this ionic solid. 相似文献
25.
We present an optical experiment which permits us to evaluate the information exchange necessary to self-induce cooperatively a well-organized pattern in a randomly activated molecular assembly. A low-power coherent beam carrying polarization and wavelength information is used to organize a surface relief grating on a photochromic polymer thin film which is photoactivated by a powerful incoherent beam. We demonstrate experimentally that less than 1% of the molecules possessing information cooperatively transmit it to the entire photoactivated polymer film. 相似文献
26.
Ewelina Chajduk Halina Polkowska-Motrenko Rajmund S. Dybczyński 《Accreditation and quality assurance》2008,13(8):443-451
This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological
samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography
with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on
Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated
by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material
Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils
all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended
as new CRMs and proficiency test samples. 相似文献
27.
Dr. Katarzyna Trzeciak Dr. Ewelina Wielgus Dr. Sławomir Kaźmierski Mehrnaz Khalaji Prof. Assoc. Marta K. Dudek Prof. Dr. Marek J. Potrzebowski 《Chemphyschem》2023,24(7):e202200884
In this work, we present results for loading of well-defined binary systems (cocrystal, solid solution) and untreated materials (physical mixtures) into the voids of MCM-41 mesoporous silica particles employing three different filling methods. The applied techniques belong to the group of “wet methods” (diffusion supported loading – DiSupLo ) and “solvent-free methods” (mechanical ball-mill loading – MeLo , thermal solvent free – TSF ). As probes for testing the guest1-guest2 interactions inside the MCM-41 pores we employed the benzoic acid ( BA ), perfluorobenzoic acid ( PFBA ), and 4-fluorobenzoic acid ( 4-FBA ). The guests intermolecular contacts and phase changes were monitored employing magic angle spinning (MAS) NMR Spectroscopy techniques and powder X-ray diffraction (PXRD). Since mesoporous silica materials are commonly used in drug delivery system research, special attention has been paid to factors affecting guest release kinetics. It has been proven that not only the content and composition of binary systems, but also the loading technique have a strong impact on the rate of guests release. Innovative methods of visualizing differences in release kinetics are presented. 相似文献
28.
Agnieszka Czakaj Ewelina Jarek Marcel Krzan Piotr Warszyski 《Molecules (Basel, Switzerland)》2021,26(19)
Ethyl lauroyl arginate (LAE) is an amino acid-based cationic surfactant with low toxicity and antimicrobial activity. It is widely used as a food preservative and component for food packaging. When stored, LAE decomposes by hydrolysis into surface-active components Nα-lauroyl–l-arginine (LAS) or dodecanoic (lauric) acid. There are only a limited number of reports considering the mechanism of surface activity of LAE. Thus, we analysed the surface tension isotherm of LAE with analytical standard purity in relation to LAE after prolonged storage. We used quantum mechanical density functional theory (DFT) computations to determine the preferred hydrolysis path and discuss the possibility of forming highly surface-active heterodimers, LAE-dodecanoate anion, or LAE-LAS. Applying molecular dynamics simulations, we determined the stability of those dimers linked by electrostatic interactions and hydrogen bonds. We used the adsorption model of surfactant mixtures to successfully describe the experimental surface tension isotherms. The real part surface dilational modulus determined by the oscillation drop method follows a diffusional transport mechanism. However, the nonlinear response of the surface tension could be observed for LAE concentration close to and above Critical Micelle Concentration (CMC). Nonlinearity originates from the presence of micelles and the reorganisation of the interfacial layer. 相似文献
29.
30.
Ewelina Janiga Gakhyun Kim Piotr J. Chmielewski Tadeusz Lis Dongho Kim Marcin Stpie 《化学:亚洲杂志》2020,15(18):2854-2858
Energy‐transfer cassettes consisting of naphthaleneimide‐fused metalloporphyrin acceptors (M=Zn and Pd) and BODIPY donors have been designed and synthesized. These systems have rigid pseudo‐tetrahedral structures with a donor‐acceptor separation of ca. 17.5 Å. Spectroscopic investigations, including femtosecond transient absorption measurements, showed efficient excitation energy transfer (EET) occurring according to the Förster mechanism. Strong fluorescence of the donor units and significant spectral overlap of the donor and acceptor subunits are prerequisites for the efficient EET in these systems. 相似文献