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排序方式: 共有208条查询结果,搜索用时 15 毫秒
41.
Pejić N Blagojević S Anić S Kolar-Anić L 《Analytical and bioanalytical chemistry》2007,389(6):2009-2017
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric
monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state
close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation
by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift
and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the
limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was
used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using
the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed. 相似文献
42.
Kralj S Cordoyiannis G Zidansek A Lahajnar G Amenitsch H Zumer S Kutnjak Z 《The Journal of chemical physics》2007,127(15):154905
The influence of controlled-pore glass (CPG) confinement on the phase behavior of octylcyanobiphenyl liquid crystal (LC) is studied by means of x-ray scattering and high precision calorimetry. For CPG samples with pore diameter 2R>24 nm, the smectic order parameter temperature dependence eta(T) reveals apparent presmectic ordering far above the bulk smectic A-nematic (SmA-N) phase transition for both nontreated and silane-treated CPG matrices. The behavior of eta(T) is qualitatively similar in all samples, well obeying the mean field approach (MFA) in which the surface wetting tendency plays the dominant role. In contrast, the critical fluctuations remain important in the specific heat data, which cannot be described within the MFA. We show experimentally that randomness and surface wetting become dominant over finite-size effects for 2R approximately<10 nm, in agreement with theoretical analysis. In nontreated samples, the noncritical character of the static disorder and the interfacial LC-CPG coupling almost completely suppress the quasi-SmA-N and nematic-isotropic phase transitions at 2R approximately 15.1 and approximately 7.5 nm, respectively. 相似文献
43.
Hunzinger C Schrattenholz A Poznanović S Schwall GP Stegmann W 《Journal of chromatography. A》2006,1123(2):170-181
In this article we evaluate methods used to reveal the molecular complexity, which is generated in biological samples by posttranslational modifications (PTM) of proteins. We show how distinct molecular differences on the level of phosphorylation sites in a single protein (ovalbumin) can be resolved with different success using 1D and 2D gel-electrophoresis and reversed-phase liquid chromatography (LC) with monolithic polystyrol-divinylbenzol (PS-DVB) columns for protein separation, and matrix-assisted laser desorption ionisation-time of flight mass spectrometry (MALDI-TOF MS) for protein identification. Phosphorylation site analysis was performed using enzymatic dephosphorylation in combination with differential peptide mass mapping. Liquid chromatography-MALDI-TOF MS coupling with subsequent on-target tryptic protein digestion turned out to be the fastest method tested but yielded low resolution for the analysis of PTM, whereas 2D gel-electrophoresis, due to its unique capability of resolving highly complex isoform pattern, turned out to be the most suitable method for this purpose. The evaluated methods complement one another and in connection with efficient technologies for differential and quantitative analysis, these approaches have the potential to reveal novel molecular details of protein biomarkers. 相似文献
44.
Nives Vladislavić Marijo Buzuk Slobodan Brinić Maša Buljac Marija Bralić 《Journal of Solid State Electrochemistry》2016,20(8):2241-2250
A study on the preparation and characterization of the potentiostatically prepared bismuth films (BiFs), in order to obtain satisfactory electroanalytical tool, is presented. BiFs formed on glassy carbon were characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The dependence of the BiFs properties upon electrolytes composition and electrochemical parameters are discussed and diagnostic criteria that allow estimation of the BiF morphology are proposed. Analytical performance data of the formed BiF electrodes were obtained by their application to the determination of glutathione (GSH) and folic acid (FA) using square-wave cathodic stripping voltammetry. The dependence of the analytical performance of the formed BiFs on their specific surface areas, along with their different morphology, is discussed. Adequate method and parameters for the electrochemical formation of optimal BiF, in order to fulfill the analytical requirements, are proposed. The best analytical performance was obtained with films formed from acetic buffer solution spiked with EDTA, as a consequence of the improved surface coverage and most arranged homogenous structure of the film. This electrode displays a linear response range toward GSH with estimated detection limit of 0.005 μM and sensitivity of 3.28 μA μM?1 for linear range of 0.01 to 0.1 μM. Also, the utilization of the BiF electrode for the determination of FA was demonstrated by direct electroreduction of FA. 相似文献
45.
46.
Zhou XJ Shi J Yoshida T Cuk T Yang WL Brouet V Nakamura J Mannella N Komiya S Ando Y Zhou F Ti WX Xiong JW Zhao ZX Sasagawa T Kakeshita T Eisaki H Uchida S Fujimori A Zhang Z Plummer EW Laughlin RB Hussain Z Shen ZX 《Physical review letters》2005,95(11):117001
High resolution angle-resolved photoemission spectroscopy data along the (0,0)-(pi,pi) nodal direction with significantly improved statistics reveal fine structure in the electron self-energy of the underdoped (La2-xSrx)CuO4 samples in the normal state. Fine structure at energies of (40-46) meV and (58-63) meV, and possible fine structure at energies of (23-29) meV and (75-85) meV, have been identified. These observations indicate that, in (La2-xSrx)CuO4, more than one bosonic modes are involved in the coupling with electrons. 相似文献
47.
<正>Coarse-graining of some sort is a fundamental and unavoidable step in any attempt to derive the classical mechanical behavior from the quantum formalism.We utilize the two-mode Bose-Hubbard model to illustrate how different coarse-grained systems can be naturally associated with a fixed quantum system if it is compatible with different dynamical algebras.Alternative coarse-grained systems generate different evolutions of the same physical quantities,and the difference becomes negligible only in the appropriate macro-limit. 相似文献
48.
Igor Serša Slobodan Macura 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):466-477
We experimentally verified a recently proposed technique for the excitation of a complicated three-dimensional profile (CARVE,completelyarbitraryregionalvolumeexcitation). CARVE is based on a generalized DANTE RF pulse sequence and a synchronous string of gradient steps. Provided there is no limitation in the number of pulses, CARVE can generate an excitation profile of any shape with any resolution. However, hardware limitations and sample properties restrict the number of RF pulses and gradient steps and, thus, limit attainable resolution of the excitation profile. We theoretically and experimentally showed that spatial resolution can be increased by distributing a long sequence among several CARVE experiments and summing up their signals. This is particularly important for three-dimensional excitation profiles where ann-fold increase in resolution requires ann3-fold increase of the number of events in the sequence. The potential use of three-dimensional CARVE might be in spectroscopic imaging where the excitation profile can be tailored to match the shape of a selected organ or body part. 相似文献
49.
Djaković-Sekulić Tatjana Lj. Perišić-Janjić Nada U. Petrović Slobodan D. 《平面色谱法杂志一现代薄层色谱法》2003,16(2):147-153
JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of para-substituted amides of α-phenylacetic, benzoic, propanoic, and 2,2-dimethylpropanoic acid... 相似文献
50.
Onjia AE Milonjić SK Todorović M Loos-Neskovic C Fedoroff M Jones DJ 《Journal of colloid and interface science》2002,251(1):10-17
The surface properties of Ni and Cu hexacyanoferrates were investigated by the inverse gas chromatography method. Retentions of 10 organic compounds were measured at zero surface coverage in the temperature range 80 to 95 degrees C. The gas/solid partition coefficients and the related thermodynamic data of adsorption (standard free energy change, standard state enthalpies, and entropy changes) also at zero surface coverage were determined. The dispersive component of free surface energy of both hexacyanoferrates, at investigated temperatures, was calculated. The surface acid/base properties were also evaluated using polar adsorbates and the results obtained indicate that nickel hexacyanoferrate is more acidic than copper hexacyanoferrate. 相似文献