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71.
Solid-phase extraction combined with dispersive liquid-liquid microextraction (SPE-DLLME) was applied for the extraction of six organophosphorous pesticides (OPPs) in water samples. The analytes considered in this study were determined by gas chromatography with mass spectrometry and included prophos, diazinon, chlorpyrifos methyl, methyl parathion, fenchlorphos and chlorpyrifos. Several extraction conditions (extraction solvent and elution/dispersion solvents nature, extraction solvent volume, elution solvent volume, water volume and sample volume) were tested for SPE-DLLME with these analytes and the best results were obtained using carbon tetrachloride as the extraction solvent and acetone as the elution/dispersion solvent. Calibration curves for the determination of OPPs in water samples were constructed in the concentration range of 10-100 ng/L. Limits of detection (LODs) ranged from 38 to 230 pg/L values that are below the maximum admissible level for drinking water (100 ng/L). Relative standard deviations (RSD) were between 8.6 and 10.4% for a fortification level of 100 ng/L. At the same fortification level, the relative recoveries (R.R.) of tap, well and irrigation water samples were in the range of 30.2-97.1%. 相似文献
72.
César Ricardo Teixeira Tarley Felipe Nascimento Andrade Fernanda Midori de Oliveira Marcela Zanetti Corazza Luiz Fernando Mendes de Azevedo Mariana Gava Segatelli 《Analytica chimica acta》2011,(2):145
A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb2+ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb2+ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L−1), eluent (HNO3) concentration (0.5 mol L−1) and preconcentration flow rate (4.0 mL min−1), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L−1 (r = 0.999) with limit of detection of 0.75 μg L−1; the precision (repeatability) calculated as relative standard deviation (n = 10) was 5.0 and 3.6% for Pb2+ concentration of 10.0 and 60.0 μg L−1, respectively. From on-line breakthrough curve, column capacity was 3.5 mg g−1. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min−1, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb2+/Cd2+, Pb2+/Cu2+ and Pb2+/Zn2+. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb2+ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb2+ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results. 相似文献
73.
José Fernando Gonçalves Mauricio G. C. Resende Jorge J. M. Mendes 《Journal of Heuristics》2011,17(5):467-486
This paper presents a biased random-key genetic algorithm for the resource constrained project scheduling problem. The chromosome
representation of the problem is based on random keys. Active schedules are constructed using a priority-rule heuristic in
which the priorities of the activities are defined by the genetic algorithm. A forward-backward improvement procedure is applied
to all solutions. The chromosomes supplied by the genetic algorithm are adjusted to reflect the solutions obtained by the
improvement procedure. The heuristic is tested on a set of standard problems taken from the literature and compared with other
approaches. The computational results validate the effectiveness of the proposed algorithm. 相似文献
74.
R.J.C LimaP.T.C Freire J.M SasakiF.E.A Melo J.Mendes FilhoM.H Lente J.A Eiras 《Solid State Communications》2003,126(6):339-342
We have investigated the behavior of the Li1.43Cs0.57SO4 single-crystal Raman spectra and dielectric permittivity as a function of temperature. It was observed that the crystal, which is an occupationally disordered system, with orthorhombic C2v2 structure at room temperature, undergoes a phase transition at 230 K. In the new phase the SO4 tetrahedra remain in two non-equivalent sites and there is no evidence of the doubling of the unit cell. 相似文献
75.
J.J. Lima-Silva J. Mendes Filho M.H. Lente D. Garcia 《Solid State Communications》2004,131(2):111-114
Lead zinc niobate-lead titanate[(1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3] (PZN-PT) crystals with x=4.5% and x=12% have been investigated using dielectric and Raman measurements over a range of temperatures. Above room temperature, dielectric measurements show that both compositions exhibit structural phase transitions according to the phase diagram proposed by Kuwata et al. [Ferroelectrics 387 (1981) 579]. Below room temperature, an anomaly at around 180 K for the x=12% sample is observed, suggesting another phase transition. Raman measurements are used to study all phase transitions. 相似文献
76.
I.O. Mazali A.G. Souza Filho B.C. Viana J. Mendes Filho O.L. Alves 《Journal of nanoparticle research》2006,8(1):141-148
In this paper we report the synthesis and characterization of TiO2 nanocrystal dispersed into a porous Vycor glass. We have obtained very small TiO2 nanocrystals in the anatase form. The nanocrystal size is controlled via the mass increment only thus preventing the growth through the coalescence process. The nanocrystal size was monitored through transmission electron microscope and Raman scattering. The␣coalescence control is attributed due to the obtention of nanocrystals dispersed into the host and to the terminal bonds present in the porous which act as an anchor thus resulting in a low diffusion of the nanocrystals through the porous network. 相似文献
77.
78.
S. Cimmino E. Di Pace E. Martuscelli L. C. Mendes C. Silvestre 《Journal of Polymer Science.Polymer Physics》1994,32(12):2025-2035
The article discusses the influence of an oligomeric resin, hydrogenated oligo (cyclopentadiene) (HOCP), on the morphology and properties of its blends with high density polyethylene (HDPE). HDPE/HOCP blends after solidification contain three phases: the crystalline phase of HDPE and two amorphous phases, one rich in amorphous HDPE and the other in HOCP. DSC thermograms and the loss modulus behaviors show that the γ transition is influenced by HOCP molecules and, in addition to the αc transition of HDPE, there is another transition that is attributed to the HOCP-rich phase. The hypothesis of the two amorphous phases is confirmed by the optical microscopy observations performed on isothermally crystallized blend films. © 1994 John Wiley & Sons, Inc. 相似文献
79.
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