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排序方式: 共有232条查询结果,搜索用时 242 毫秒
61.
Aurora Martín-Calero Juan H. Ayala Venerando González Ana M. Afonso 《Analytical and bioanalytical chemistry》2009,394(4):937-946
The beneficial effects of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF4) ionic liquid (IL) as mobile phase additive, desorption solvent, and memory effect suppressor in solid-phase microextraction (SPME)–high-performance liquid chromatography with fluorescence detection for the determination of six heterocyclic aromatic amines have been evaluated for the first time. Several chromatographic parameters have been evaluated in the presence or absence of IL or using triethylamine as the most common mobile phase additive, with a Nova-Pak® C18 stationary phase. This IL was found to be clearly superior to triethylamine for efficiency as well as peak shape enhancement and sensitivity increase. SPME was chosen because it is faster than conventional extraction techniques and allowed us to minimize the use of organic solvents. However, memory effect may become a problem when a high-sensitivity detector is used. The appropriate conditions for the desorption step and to eliminate the memory effect involving BMIm-BF4 were established and optimized. The method was applied for the determination of these compounds in commercial meat extracts. 相似文献
62.
Semi-covalent imprinted polymer using propazine methacrylate as template molecule for the clean-up of triazines in soil and vegetable samples 总被引:1,自引:0,他引:1
Cacho C Turiel E Martín-Esteban A Ayala D Pérez-Conde C 《Journal of chromatography. A》2006,1114(2):255-262
A semi-covalent imprinted polymer was prepared by precipitation polymerisation using propazine methacrylate as template molecule, ethylene glycol dimethacrylate as cross-linker and toluene as porogen. After removal of propazine by basic hydrolysis of the covalent bond, the optimum loading, washing and elution conditions for the solid-phase extraction of the selected triazines were established. The binding sites present in the polymeric matrix were characterised by fitting the experimental results of several rebinding studies to the Langmuir-Freundlich isotherm. Subsequently, an analytical methodology based on molecularly imprinted solid-phase extraction (MISPE) was developed for the determination of several triazinic herbicides in soil and vegetable samples. Following this procedure, a good degree of clean-up of the sample extracts was easily achieved, allowing the HPLC-UV determination of selected triazines in complex samples at low concentration levels. 相似文献
63.
Experimental preparation and UV/IR spectroscopic characterization of 1,3-dibutanal-1,2,4,5-tetroxane
Ayala DA Romero JM Jorge NL Gómez-Vara ME Jubert AH Castro EA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,64(3):717-721
We report the experimental preparation of the 1,3-butanal-1,2,4,5-tetroxane by oxidation of glutataldehyde with oxygen peroxide in presence of concentrated sulfuric acid, following the Bayer and Viller method modified by Jorge et al. The UV and IR spectra are studied from the experimental and theoretical standpoint. A rather complete vibrational assignment was performed and the nature of the electronic transitions was discussed in detail. 相似文献
64.
Conde FJ Afonso AM González V Ayala JH 《Analytical and bioanalytical chemistry》2006,385(7):1162-1171
A sampling and analysis method for the determination of 21 phenolic compounds in smoke samples from biomass combustion has
been developed. The smoke is used to make smoked foods, following an artisanal procedure used in some parts of the Canary
Islands. The sampling system consists of a Bravo H air sampler, two impingers, each one containing an aqueous solution of
sodium hydroxide 0.1 mol L−1, followed by a silica gel trap. The variables optimized to reach the best sampling conditions were volume of absorbent solution
and sampling flow. Under the optimum conditions, 100 mL of absorbent solution of NaOH 0.10 mol L−1 and 2 L min−1 for the sampling flow, sampling efficiencies are higher than 80%. Analysis of phenolic compounds was carried out by headspace
solid-phase microextraction (HS-SPME) coupled to gas chromatography–mass spectrometry (GC-MS). Five different fiber coatings
were employed in this study. By means of a central composite design, extraction time, salt concentration, and pH of the solution
were optimized: 65-μm carbowax–divinylbenzene, extraction time 90 min, concentration in NaCl of 35% (m/v), and pH 2 yielded
the highest response. Detection limits of phenol and their alkyl derivatives, guaiacol and eugenol, are between 1.13 and 4.60 ng mL−1. 3-Methoxyphenol, 2,6-dimethoxyphenol, and vanillin have detection limits considerably higher. Good linearity (R
2≥0.98) was observed for all calibration curves in the established ranges. The reproducibility of the method (RSD, relative
standard deviation) was found to oscillate between 7 and 18% (generally close or lower than 10%). 相似文献
65.
66.
A simple and rapid method is developed for extraction and determination of polycyclic aromatic hydrocarbons (PAHs) in marine sediments. The procedure was based on the microwave-assisted extraction of PAHs in marine sediment samples using a micellar medium of Polyoxyethylene 10 lauryl ether as extractant. Two-level factorial designs have been used to optimize the microwave extraction process. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 85.70 and 100.73%, with a relative standard deviation of 1.77-7.0% for PAHs with a ring number higher than three. 相似文献
67.
M. Miranda-Hernández J. Ayala Marina E. Rincón 《Journal of Solid State Electrochemistry》2003,7(5):271-276
In this work we study the effect of surface structure on the charge storage capacity of carbon black electrodes with various
changes in surface chemistry, morphology, and doping species. Cyclic voltammetry and chronopotentiometry studies, performed
under alkaline conditions with carbon paste electrodes, indicate the importance of surface structure and grain size on the
faradic and capacitive charge contributions of these materials. Among the various carbon blacks studied, the lithiated material
shows superior charge storage capacity, suggesting the importance of alkaline metals and oxygenated groups on the carbon surface.
For the graphitic carbon, the appearance of a reversible redox process with cycling resembles the electrochemical behavior
reported for hydrogen storage in carbon nanotubes.
Electronic Publication 相似文献
68.
69.
In this present study the extraction of polycyclic aromatic hydrocarbons (PAHs) from marine sediments with a micellar medium of Polyoxyethylene 10 lauryl ether by an ultrasound-assisted method has been studied. Factorial design experiments were used in order to optimize the extraction parameters: extraction time, surfactant concentration and surfactant volume:amount of sediment relationship. The results suggest that surfactant concentration is statistically the most significant factor. The analysis of extracts has been carried out by HPLC with UV detection. Fortified sediments gave an average recovery between 86.7 and 106.6%, with relative standard deviation of 2.02-6.83% for PAHs with a ring number higher than three. 相似文献
70.
Néstor M. Carballeira David Sanabria Norma L. Ayala Clarisa Cruz 《Tetrahedron letters》2004,45(19):3761-3763
A stereoselective synthesis for the (5Z,9Z)-14-methyl-5,9-pentadecadienoic acid and the monounsaturated analog (Z)-14-methyl-9-pentadecenoic acid was accomplished in six to seven steps where double alkyne coupling was the key step. This synthesis will facilitate the study of the topoisomerase I inhibitory profile of this important class of fatty acids. 相似文献