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81.
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83.
The interaction of 1-naphthol-N-methyl-carbamate (carbaryl) and its degradation product, 1-naphthol, with the surfactant hexadecyl-trimethylammonium bromide has been studied. The micellar medium allows the direct spectrofluorimetric determination of carbaryl, with 6.2 ng/ml as detection limit in acidic medium, or indirectly, after hydrolysis, as 1-naphthol at pH 11.0 or pH 3.0 with detection limits of 0.4 and 1.6 ng/ml, respectively. The recoveries of carbaryl and 1-naphthol from natural waters are acceptable. 相似文献
84.
85.
Solid-phase microextraction coupled with high-performance liquid chromatography for the analysis of heterocyclic aromatic amines 总被引:3,自引:0,他引:3
Solid-phase microextraction (SPME) coupled with high-performance liquid chromatography (HPLC) with UV diode array detection (DAD) for the analysis of heterocyclic aromatic amines (HAs) is described. Four kinds of fiber coatings: Carbowax-templated resin (CW-TPR), Carbowax-divinylbenzene (CW-DVB), poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) and polyacrylate (PA) were evaluated for extraction of nine most biologically active heterocyclic aromatic amines. Different parameters affecting to the microextraction and determination of HAs were studied, such as absorption and desorption time, desorption mode, composition of the solvent for desorption, pH, ionic strength, and percentage of methanol in the sample. To determine these amines in food samples a new simplified procedure is proposed, consisting of treatment of the sample with methanolic NaOH prior microextraction by CW-TPR fiber coating and HPLC-DAD determination. The advantages of this new method are the reduced amounts of time and organic solvents required. 相似文献
86.
Cabrita EJ Afonso CA de Oliveira Santos AG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(7):1455-1467
Studies aimed at the development of new synthetic pathways for the preparation of chiral cyclic oxaza and diaza phosphoramides suitable for use in asymmetric chemistry led us to the investigation of the imide -amide rearrangement of cyclic phosphorimidates. As a result of this work new types of oligomeric organophosphorus compounds, formed by a novel 1,4-addition type ring opening polymerisation, were identified. These compounds are the stable intermediates of the imide-amide rearrangement, which upon heating yield the previously reported rearranged product. A detailed study of the mechanism of the Lewis acid catalysed imide-amide rearrangement and stereochemical control of the final products is reported. As a result, the full mechanism was elucidated and evidence of retention of configuration at the rearranged carbon atom is presented. Substituent effects were rationalised based on molecular modelling calculations. 相似文献
87.
M. Dos Santos Afonso Cecilia Di Risio M. Zysmilich Roberto O. Marqués M.A. Blesa 《Radiation Physics and Chemistry》1996,48(6):715-718
The influence of gamma and reactor (n + γ) preirradiation on the dissolution of magnetite microcrystals synthetized by a low-temperature wet method was studied. Two opposite effects affect the dissolution rate: the annealing due to the gamma radiation and the generation of new imperfect coordination polyhedra. A model for the kinetic processes was proposed and the kinetic parameters were calculated. 相似文献
88.
Argelio González Rosa M. Linares Juan H. Ayala Ana M. Afonso Venerando González 《Mikrochimica acta》1995,118(3-4):153-162
The effect of cationic micelles of benzyldimethylhexadecylammonium chloride and hexadecyltrimethylammonium bromide on the fluorescence spectra of indole and its carboxylic derivatives were determined. The larger solute-micelle binding constants were provided by benzyldimethylhexadecylammonium chloride, ranging from 0.10·105 and 2.15·105
M
–1 for indole-5-carboxylic and indole-2-carboxylic acid, respectively. The determination of indole-4-carboxylic acid with a detection limit of 1.0 ng ml–1, in the presence of the 3-and 5-substituted derivatives, shows the analytical potential of the synchronous spectrofluorimetry combined with the enhancement effects caused by micellar media. 相似文献
89.
90.
Eurico J. S. Cabrita António G. O. Santos Carlos A. M. Afonso 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1)
Abstract The imide-amide rearrangement of cyclic phosphorirnidates 1 leads to the formation of phosphoramidates 3, either thermally (> 180°C) or by the action of a Lewis acid (BF3 OEt2, 60°C)1. In an attempt to develop a synthetic pathway to β aminoalcohols based on this rearrangement, we have thoroughly studied the influence of the structure of the reactants on the Lewis acid catalysed rearrangement. This study brought some insight into the mechanism of this particular reaction, namely the identification of a new polymeric structure 2. not yet described, which is converted into 3 by thermolysis2. The formation of 2 at rt was followed by 3 P NMR. In the case of R′? Ph, the reactivity observed for R2N was: i-Pr2N > Pyrrolidine > n-Bu2N For R2=i-Pr2, the observed R′ group effect was: Bn > 4-NO2Bn > Ph. No reaction was observed for R′ ? Ts, n-Oct. In the case of the groups R′ ? Bn and R2=i Pr2 the Lewis acid effect was also studied: BF3OEt2, BF3MeOr-Bu, Sc(OTf)3 or CITi(Oi-Pr)3 or Me2SnCl2. 相似文献