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11.
Jandera P Skeifíková V Rehová L Hájek T Baldriánová L Skopová G Kellner V Horna A 《Journal of separation science》2005,28(9-10):1005-1022
Methods were developed for the analysis of natural antioxidants including phenolic compounds and flavonoids in beverages and plant extracts using gradient HPLC with multi-channel electrochemical coulometric detection. Suitability of various reversed-phase columns for this purpose was compared; pH and mobile phase gradients were optimized with respect to the separation selectivity and sensitivity of detection. Because of different target compounds in various sample types, the overlapping resolution maps and the normalized resolution product approaches described earlier were used to select optimum columns and gradients to suit the analysis of the individual sample types. The methods were applied to the analysis of phenolic compounds and flavonoids in beer, wine, tea, and yacon extracts. 32 phenolic compounds were identified and determined, including derivatives of benzoic and cinnamic acids, flavones, and a few related glycosides. Eight-channel CoulArray detection offers high selectivity and sensitivity with limits of detection in the low microg L(-1) range, at least an order of magnitude lower than single-channel coulometric detection using the Coulochem detector. No special sample pretreatment is necessary and, because of the compatibility of the CoulArray detector with gradient elution, phenolic antioxidants of different polarities can be determined in a single run. In addition to the retention times, the ratios of the areas of the pre-dominant and post-dominant peaks to the area of the dominant peak can be used for improved identification of natural antioxidants. 相似文献
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Veronika Pilařová Tomáš Gottvald Pavel Svoboda Ondřej Novák Karolína Benešová Sylvie Běláková Lucie Nováková 《Analytica chimica acta》2016
The goal of this study was to develop an effective supercritical fluid chromatography method using single quadrupole MS for analysis of all isomeric forms of vitamin E. Finally, two fast and effective methods, the high resolution one and the high speed one, for the determination of 8 vitamin E isomers in human serum were developed. 相似文献
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A comparative alcoholysis study of N-silylated derivatives of simple heterocyclic carboxamides (lactams, imides, ureas) is presented. The second-order rate constant values span a range as wide as three orders of magnitude. On the basis of DFT calculations, a good correlation between reactivity and the Si?O distance was found within each family of compounds. The viability of two different reaction pathways was evaluated using a detailed computational mechanistic study of the methanolysis of cyclic urea homologues. Peculiarities in the single-crystal X-ray diffraction structures of the trimethylsilyl and trimethylsiloxy phthalimides are also discussed. 相似文献
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Veronika Scholtyssek 《Numerical Functional Analysis & Optimization》2013,34(9-10):925-944
The inverse eigenvalue problem for symmetric matrices (IEP) is formulated as a system of two matrix equations. For solving the system a variation of Newton's method is used which has been proposed by Fusco and Zecca [Calcolo XXIII (1986), pp. 285–303] for the simultaneous computation of eigenvalues and eigenvectors of a given symmetric matrix. an iteration step of this method consists of a Newton step followed by an orthonormalization with the consequence that each iterate satisfies one of the given equations. The method converges locally y quadratically to regular solutions. The algorithm and some numerical examples are presented. In addition, it is shown that the so called Method III proposed by Friedland, Nocedal, and Overton [SIAM J. Numer. Anal.,24 (1987), pp. 634–667] for solving IEP may be constructed similarly to the method presented here 相似文献
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Ceren Kütahya Nicolai Meckbach Prof. Dr. Veronika Strehmel Prof. Dr. Jochen S. Gutmann Prof. Dr. Bernd Strehmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(46):10444-10451
NIR exposure at 790 nm activated photopolymerization of monomers comprising UV-absorbing moieties by using [CuII/(TPMA)]Br2 (TPMA=tris(2-pyridylmethyl)amine) in the ppm range and an alkyl bromide as initiator. Some of them comprised structural elements selected either from those showing proton transfer or photocycloaddition upon UV excitation. Polymers obtained comprise living end groups serving as macroinitiator for controlled synthesis of block copolymers with relatively narrow molecular weight distributions. Chromatographic results indicated formation of block copolymers produced by this synthetic approach. Free-radical polymerization of monomers pursued for comparison exhibited the expected broader dispersity of molecular weight compared to photo-ATRP. Polymerization of these monomers by UV photo-ATRP failed on the contrary to NIR photo-ATRP demonstrating the UV-filter function of the monomers. This work conclusively provides a new approach for the polymerization of monomers comprising UV-absorbing moieties through photo-ATRP in the NIR region. This occurred in a simple and efficient pathway. However, studies also showed that not all monomers chosen successfully proceeded in the NIR photo-ATRP protocol. 相似文献
17.
Advanced Sensing of Antibiotics with Magnetic Gold Nanocomposite: Electrochemical Detection of Chloramphenicol 下载免费PDF全文
Dr. Petr Jakubec Dr. Veronika Urbanová Dr. Zdenka Medříková Prof. Dr. Radek Zbořil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14279-14284
The sensing and accurate determination of antibiotics in various environments represents a big challenge, mainly owing to their widespread use in medicine, veterinary practice, and other fields. Therefore, a new, simple electrochemical sensor for the detection of antibiotic chloramphenicol (CAP) has been developed in this work. The amplification strategy of the sensor is based on the application of magnetite nanostructures stabilized with carboxymethyl cellulose (Fe3O4‐CMC) and decorated with nanometer‐sized Au nanoparticles (NPs) (Fe3O4‐CMC@Au). In this case, CMC serves as a stabilizing agent, preventing the aggregation of Fe3O4 NPs, and hence, enabling the kinetic barrier for electron transport to be overcome, and the Au NPs serve as an electron‐conducting tunnel for better electron transport. As a proof of concept, the developed nanosensor is used for the detection of CAP in human urine samples, giving a recovery value of around 97 %, which indicates the high accuracy of the as‐prepared nanosensor. 相似文献
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Karel Kolomazník Ji?í Pecha Veronika Friebrová Dagmar Janá?ová Vladimír Va?ek 《Heat and Mass Transfer》2012,48(9):1505-1512
Biostimulators are substances able to enhance the immune system of cultivated crops and support plant metabolism. Their utilization helps to reduce the amount of chemicals used in agriculture. To perform the desired effect, a biostimulator must be able to penetrate into the plant tissue. The time of penetration however, is limited, since the biostimulator must remain in a liquid state. This is of great importance—especially in field conditions, where the treated plants are exposed to different weather condition and other extrinsic factors. A mathematical model based on diffusion mechanisms has been elaborated to describe the biostimulator transport process from penetration of the leaves into the plant’s inner tissues. By means of the effective diffusion coefficient of the prepared specific protein hydrolyzate, this model can be used to estimate the time necessary for the uptake of the minimal active amount of the biostimulator. 相似文献