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191.
Phoebe Y. T. Hon Man-ying Wan Della W. M. Sin Yiu-chung Wong 《Analytical and bioanalytical chemistry》2013,405(23):7241-7250
This paper describes a metrological approach to evaluate the measurement capability of laboratories participating in two proficiency testing (PT) programmes involving the analysis of five polycyclic aromatic hydrocarbons (PAHs) in sediment samples. Reference values of PAHs in the programmes for performance assessment were obtained from an accurate isotope dilution gas chromatography mass spectrometry (ID-GCMS) method which was thoroughly validated and verified. Isotope dilution mass spectrometry (IDMS) technique usually has a well-defined measurement uncertainty budget and a traceability link to an International System of Units. Provision of the metrological reference values in PT enables the establishment of a technical platform to assess the actual competence of the participating laboratories in sediment PAHs analysis. Results of the PT programmes showed that about 80 % of the laboratories employed gas chromatography in their analyses and the remaining used liquid chromatography. Irrespective of the techniques being used, however, the majority of the participating laboratories were observed to underestimate values in which the mean values of the five reported PAHs were less than those of the ID-GCMS-derived reference values by 13–20 %. Only 41–44 % of the participating laboratories were able to achieve satisfactory z-scores. The present study revealed that the reinforcement of the capability for accurate measurement of PAHs in sediment samples in laboratories worldwide should be addressed. 相似文献
192.
Laetitia Shintu Stefano Caldarelli Mylène Campredon 《Analytical and bioanalytical chemistry》2013,405(28):9093-9100
In this paper, we present for the first time the use of high-resolution magic angle spinning nuclear magnetic resonance (HRMAS NMR) spectroscopy combined with chemometrics as an alternative tool for the characterization of tobacco products from different commercial international brands as well as for the identification of counterfeits. Although cigarette filling is a very complex chemical mixture, we were able to discriminate between dark, bright, and additive-free cigarette blends belonging to six different filter-cigarette brands, commercially available, using an approach for which no extraction procedure is required. Second, we focused our study on a specific worldwide-distributed brand for which established counterfeits were available. We discriminated those from their genuine counterparts with 100 % accuracy using unsupervised multivariate statistical analysis. The counterfeits that we analyzed showed a higher amount of nicotine and solanesol and a lower content of sugars, all endogenous tobacco leaf metabolites. This preliminary study demonstrates the great potential of HRMAS NMR spectroscopy to help in controlling cigarette authenticity. Figure
Prediction of the authenticity of smuggled B2 cigarettes. All of them were further established as counterfeits 相似文献
193.
Clemente Bretti Concetta De Stefano Claudia Foti Silvio Sammartano 《Journal of solution chemistry》2013,42(7):1452-1471
The protonation constants and solubilities of three complexons [ethylenediamine-N,N′-disuccinic acid (EDDS), ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) and 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CDTA)] are reported in aqueous solutions of NaCl with different ionic strength values (0 ≤ I ≤ 4.8 mol·L?1) and, in the case of CDTA, in (CH3)4NCl (0.1 ≤ I ≤ 2.7 mol·L?1). The dependence on ionic strength of the protonation constants of these three complexons and four other complexons that were previously reported (NTA, EDTA, DTPA and TTHA), is analyzed in NaCl solution; the ionic strength influences quite strongly the protonation constants (as an example for CDTA, log10 K 1 = 10.54 and 9.25 at I = 0.1 and 1 mol·L?1, respectively), while the effect of (CH3)4NCl concentration is lower. Based on the total solubility S T and the protonation constant data at different salt concentrations, the solubility of the neutral species S 0 and the solubility products K S0 are obtained. The Setschenow coefficients k m and the solubility values S 0 0 in pure water are also reported (S 0 0 = 0.55, 0.21 and 0.75 mmol·kg?1 for EDDS, EGTA and CDTA, respectively). The dependence of the protonation constants on ionic strength is also interpreted in terms of ion pair formation, and the formation constants of Na+ species are reported. 相似文献
194.
Abstract Phase diagrams of chiral nematic liquid crystals are studied within the framework of a generalized Landau-Ginzburg-de Gennes theory. Using the parametrization of Grebel, Hornreich, and Shtrikman for the tensor order parameter Q, all relevant elastic terms are included for the helicoidal phase and the blue phases of chiral nematic liquid crystals up to fourth order in Q and its gradient ?Q. The influence of the additional elastic terms on the phase diagrams of the chiral nematic phases is then investigated. The theory correctly describes the variation of the pitch with temperature and the induced biaxiality of the cholesteric phase. The results resolve the discrepancies encountered by Hornreich and Shtrikman in the comparison of experiment and theory. New features in the topology of the phase diagrams of blue phases, like re-entrant phase transitions, are predicted. 相似文献
195.
Walter Vastarella Livia Della Seta Amedeo Masci Jan Maly Manuela De Leo Ligia Maria Moretto 《International journal of environmental analytical chemistry》2013,93(10-11):701-714
Gold nanowires were synthesized within polycarbonate membranes according to an electroless deposition method, obtaining nanoelectrode ensembles (NEEs) with special electrochemical features. NEEs were coupled with home-produced carbon graphite screen printed electrodes and the electrochemical properties of the original nanoelectrode ensemble on screen printed substrate (NEE/SPS) assembly has been tested for sensors application. Glucose oxidase has been used as model enzyme in order to verify the feasibility of disposable gold NEE/SPS biosensors. Finally, different immobilisation and electrochemical deposition techniques based on either self assembled monolayers of cysteamine (CYS) or amino-propyl-triethoxysilane (APTES) and conductive polyaniline (PANI) molecular wires were used. Spatial patterning of the enzyme on the polycarbonate surface and of PANI wires on gold nanoelectrodes was obtained. Possible direct electron transfer between the enzyme and the PANI modified gold nanoelectrodes has been evaluated. 相似文献
196.
Mohammad Hayatifar Claudia Forte Guido Pampaloni Yury V. Kissin Anna Maria Raspolli Galletti Stefano Zacchini 《Journal of polymer science. Part A, Polymer chemistry》2013,51(19):4095-4102
This report describes propylene polymerization reactions with titanium complexes bearing carbamato ligands, Ti(O2CNMe2)Cl2 ( I ) and Ti(O2CR2)4 [R2 = NMe2 ( II ), NEt2 ( III ) and ( IV )]. Combinations of these complexes and MAO form catalysts for the synthesis of atactic polypropylene, as confirmed by FT‐IR, DSC and 13C NMR analysis. Effects of main reaction parameters on the catalyst activity were studied including the type of complex, solvent, temperature, and the [Al]/[Ti] molar ratio. The highest activity was observed when chlorobenzene was used as a solvent and AlMe3‐depleted MAO was employed as a cocatalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4095–4102 相似文献
197.
Dr. Oscar Francesconi Prof. Cristina Nativi Dr. Gabriele Gabrielli Matteo Gentili Marco Palchetti Beatrice Bonora Dr. Stefano Roelens 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(35):11742-11752
Synthetic ditopic receptors, designed for the molecular recognition of dimannosides, have been prepared by bridging two monotopic units effectively recognizing mannosides with linkers of the appropriate size and flexibility, endowed with hydrogen‐bonding groups. Affinities toward the α and β glycosides of the biologically relevant Manα(1–2)Man disaccharide were measured by NMR spectroscopy and isothermal titration calorimetry (ITC) in polar organic media (30–40 % DMF in chloroform). Significant selectivities and affinities in the micromolar range were observed in most cases, with two newly designed receptors being the most effective receptors of the set, together with a distinct preference of the dimannosides for the (S) enantiomer of the receptor in all cases. A 3D view of the recognition mode was elucidated by a combined NMR spectroscopic/molecular modeling approach, showing the dimannoside included in the cleft of the receptor. Compared to the monotopic precursors, the ditopic receptors showed markedly improved recognition properties, proving the efficacy of the modular receptor design for the recognition of disaccharides. 相似文献
198.
Joel Malmgren Dr. Stefano Santoro Dr. Nazli Jalalian Prof. Fahmi Himo Prof. Berit Olofsson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10334-10342
Phenols, anilines, and malonates have been arylated under metal‐free conditions with twelve aryl(phenyl)iodonium salts in a systematic chemoselectivity study. A new “anti‐ortho effect” has been identified in the arylation of malonates. Several “dummy groups” have been found that give complete chemoselectivity in the transfer of the phenyl moiety, irrespective of the nucleophile. An aryl exchange in the diaryliodonium salts has been observed under certain arylation conditions. DFT calculations have been performed to investigate the reaction mechanism and to elucidate the origins of the observed selectivities. These results are expected to facilitate the design of chiral diaryliodonium salts and the development of catalytic arylation reactions that are based on these sustainable and metal‐free reagents. 相似文献
199.
Dr. Antonello Di Crescenzo Dr. Luca Bardini Dr. Bruna Sinjari Dr. Tonino Traini Dr. Lisa Marinelli Dr. Mauro Carraro Prof. Raimondo Germani Dr. Pietro Di Profio Prof. Sergio Caputi Prof. Antonio Di Stefano Prof. Marcella Bonchio Prof. Francesco Paolucci Prof. Antonella Fontana 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16415-16423
Novel hydrogel phases based on positively charged and zwitterionic surfactants, namely, N‐[p‐(n‐dodecyloxybenzyl)]‐N,N,N‐trimethylammonium bromide (pDOTABr) and p‐dodecyloxybenzyldimethylamine oxide (pDOAO), which combine pristine carbon nanotubes (CNTs), were obtained, thus leading to stable dispersions and enhanced cross‐linked networks. The composite hydrogel featuring a well‐defined nanostructured morphology and an overall positively charged surface was shown to efficiently immobilise a polyanionic and redox‐active tetraruthenium‐substituted polyoxometalate (Ru4POM) by complementary charge interactions. The resulting hybrid gel has been characterised by electron microscopy techniques, whereas the electrostatic‐directed assembly has been monitored by means of fluorescence spectroscopy and ζ‐potential tests. This protocol offers a straightforward supramolecular strategy for the design of novel aqueous‐based electrocatalytic soft materials, thereby improving the processability of CNTs while tuning their interfacial decoration with multiple catalytic domains. Electrochemical evidence confirms that the activity of the catalyst is preserved within the gel media. 相似文献
200.