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251.
Sergio García-Fonseca Ana Ballesteros-GómezSoledad Rubio Dolores Pérez-Bendito 《Journal of chromatography. A》2010,1217(16):2376-2382
A supramolecular solvent made up of reverse micelles of decanoic acid, dispersed in a continuous phase of THF:water, was proposed for the simple, fast and efficient microextraction of OTA in wheat prior to liquid chromatography-fluorescence determination. The method involved the stirring of 300 mg-wheat subsamples (particle size 50 μm) and 350 μL of supramolecular solvent for 15 min, subsequent centrifugation for 15 min and the direct quantitation of OTA in the extract, previous 5.7-fold dilution with ethanol/water/acetic acid (49.5/49.5/1), against solvent-based calibration curves. No clean-up of the extracts or solvent evaporation was needed. Interactions between the supramolecular solvent and major matrix components in the wheat (i.e. carbohydrates, lipids and proteins) were investigated. The reverse micelles in the extractant induced gluten flocculation but only in the coacervation region of lower analytical interest (i.e. at percentages of THF above 11%). The quantitation of OTA was interference-free. Representativity of the 300 mg-wheat subsamples was proved by analysing a reference material. OTA recoveries in wheat ranged between 84% and 95% and the precision of the method, expressed as relative standard deviation, was 2%. The quantitation limit of the method was 1.5 μg kg−1 and was below the threshold limit established for OTA in raw cereals by EU directives (5.0 μg kg−1). The method developed was validated by using a certified reference material and it was successfully applied to the determination of OTA in different wheat varieties from crops harvested in the South of Spain. OTA was not detected in any of the analysed samples. This method allows quick and simple microextraction of OTA with minimal solvent consumption, while delivering accurate and precise data. 相似文献
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Verónica de la Fuente Dipl.‐Chem. Mark Waugh Dr. Graham R. Eastham Dr. Jonathan A. Iggo Dr. Sergio Castillón Prof. Dr. Carmen Claver Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6919-6932
Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes [Pd(O3SCH3)(L‐L)][O3SCH3] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex [Pd(O3SCH3)(L‐ L)][O3SCH3], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism. 相似文献
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Oreste Senofonte Nicola Violante Sonia D'Ilio Stefano Caimi Antonio Peri Sergio Caroli 《Microchemical Journal》2001,69(3)
In the framework of the Human Biology and Medicine Project of the National Program for Research in Antarctica (Programma Nazionale di Ricerche in Antartide, PNRA) a study was undertaken to explore the suitability of trace element determination in human hair as a tool for the early detection of the impact of extreme environmental conditions on the health of members of the Italian and French expeditions. This study included three campaigns, namely, the 1995–1996 expedition to the Italian base of Terra Nova Bay, as well as the 1997–1998 and 1998–1999 expeditions to both the Italian base of Terra Nova Bay and the Italian–French base of Dome C. Sampling of hair of participants in the expeditions was carried out both prior to departure and at the end of the period spent at the bases. As regards storage, pre-treatment and analysis of hair samples they were performed in accordance with previously established procedures. Acid-assisted microwave digestion was adopted as the best approach for preparing solutions for subsequent analysis by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. In the first part of this study, only the elements Ca, Cu, Fe, Mg and Zn were selected, while at a later stage it was decided to also include Co, Cr, Mn, Mo and Ni. Experimental results were subjected to basic statistical analysis to detect possible significant differences in element concentrations that occurred during the sojourn at the bases, with a view to identify possible remedial action to minimize adverse consequences. 相似文献
258.
Sergio Peris Bartosz Tylkowski Joan Carles Ronda Ricard Garcia‐Valls José Antonio Reina Marta Giamberini 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5426-5436
Two new polyethers, bearing azobenzene moiety in the side chain, were synthesized in excellent yields by means of anionic polymerization of 4‐glycidyloxyazobenzene and 4‐cyano‐4′‐glycidyloxyazobenzene (leading to azo‐P1 and azo‐P2 polymers, respectively) with the system polyiminophosphazene base t‐Bu‐P4/3,5‐di‐tert‐butylphenol as initiator. The polymers were characterized with respect to their molecular weights, structure, and calorimetric features. The polyether bearing cyanoazobenzene group in the side chain was found to exhibit nematic phase up to 200 °C. E–Z isomerization of both polymers in tetrahydrofuran solution, after irradiating with UV light at 364 nm for 15 min, was investigated by means of UV–visible absorption spectroscopy. In the case of glycidylic monomers as well as the resulting polymers, E–Z isomerization was also investigated by means of 1H NMR, by direct irradiation in the NMR probe in deuterated 1,1,2,2‐tetrachloroethane solution. By this technique, in the case of 4‐cyano‐4′‐glycidyloxyazobenzene, it was found that irradiation led to a photostationary state corresponding to an amount of Z isomer equal to 25%. For azo‐P1 polymer, Z–E or “reverse” isomerization was investigated at 60, 70, or 80 °C directly in the NMR probe; as expected, the process followed a first‐order rate law. The kinetic constants as well as the activation energy for the process were determined in this temperature range. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5426–5436, 2009 相似文献
259.
Laura Gherardi Daniela Bettinelli Sergio Spreafico Fedor G m ry 《Physica C: Superconductivity and its Applications》1998,310(1-4):52-56
Transport AC losses measured in self-field conditions on multifilamentary Bi-2223 tapes are often found to be lower than those calculated within the framework of the critical state model for a bulk wire with elliptical cross section, though generally higher than predicted for a strip. This effect is sometimes ascribed to the non-ideal geometry of the tapes, which does not exactly reproduce either shape. Here we propose an alternative explanation assuming that the critical current density of superconducting material depends on magnetic field. In practice, we analyzed the AC loss curve and deduced different Ic values for the individual data points, using the standard Norris equation for elliptical conductor. This gives the relation between ‘calculated' Ic and the self-field associated to AC transport current, which can be regarded as an alternative way to qualify the dependence of Jc on magnetic field. Important is that this procedure covers the range of fields below the self-field at Ic where the measurement in background DC field can not be used to determine Jc(B). 相似文献
260.
We study the asymptotic behavior of the free energy for a model (defined by Sinai) of one-dimensional random walk with random potential. In particular, we obtain a central limit theorem and a strong law of large numbers for this free energy. We use some results on the free energy to study some sample path properties of this random walk which are related respectively to its recurrence and localization. Some exponents describing the recurrence and localization are found. 相似文献