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131.
Cloud point extraction for determination of cadmium in soft drinks by thermospray flame furnace atomic absorption spectrometry 总被引:3,自引:0,他引:3
Cloud point extraction (CPE) is proposed as a preconcentration procedure for the determination of Cd in soft drinks by thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The cadmium reacted with pyridyl-azo-naphthol (PAN) to form hydrophobic chelates, which were extracted into the micelles of Triton X-114 in a solution buffered at pH 9. NaCl was used for the phase separation. The variables which affect the preconcentration were optimized using a 23 factorial design and central composite design (CCD). A response surface maximum point was obtained, and the critical values were a concentration of 0.13 mmol L? 1 PAN, 0.03% m/v Triton X-114 and 2.3% m/v NaCl. Under the optimized conditions, after the extraction and preconcentration steps, a sample volume of 100 μL was introduced into the hot Ni tube using water as the carrier at a flow rate of 0.4 mL min? 1. The values obtained for the detection limit, relative standard deviation and preconcentration factor were 0.0178 μg L? 1, 4.1% (n = 8) and 55.5, respectively. The accuracy of the proposed method was demonstrated by performing addition-recovery experiments. Recoveries varied from 88 to 104%. 相似文献
132.
Luiz Gustavo Lacerda Tiago André Denck Colman Tabata Bauab Marco Aurélio da Silva Carvalho Filho Ivo Mottin Demiate Eliane Carvalho de Vasconcelos Egon Schnitzler 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1893-1899
The avocado (Persea americana, Miller) is a tree that is native to Central/North America (Mexico) and it is very popular worldwide due to its food applications. Its seeds contain an important amount of starch and there is lack of study and understanding regarding the physico-chemical properties of this biopolymer. In this research, starch granules were extracted from avocado seeds and oxidised with standard sodium hypochlorite solutions at 0.5, 1.0 and 2.0 %. Untreated and modified samples were investigated using the following techniques: simultaneous thermogravimetry–differential thermal analysis, differential scanning calorimetry, non-contact atomic force microscopy, rapid viscoamylographic analysis and X-ray powder patterns diffractometry. The main purpose was to investigate the thermal, structural and rheological behaviour of native and oxidised avocado starch, and it was verified that the treated samples showed a decrease in gelatinisation enthalpy and average roughness as well as in the degree of relative crystallinity and pasting properties. 相似文献
133.
Iriux Almodovar Wilson Cardona Tomás Delgado-Castro Gerald Zapata-Torres Marcos Caroli Rezende Ramiro Araya-Maturana 《Journal of the Iranian Chemical Society》2014,11(4):1021-1026
Competing reduction and cycloaddition products were formed in the reaction of 8,8-dimethylnaphthalene-1,4,5(8H)-trione with a hydroxysulfinyldiene. The ratio of reduction to cycloaddition products depended on the stereochemistry of the diene and on the solvent employed, being higher in ethanol than in benzene. The ratio was also affected by the addition of Lewis acids, decreasing in the order BF3 = Al2O3 > MgCl2 > ZnCl2. The results help to explain and predict the occurrence of these competing processes in Diels–Alder cycloadditions involving quinonedienophiles. 相似文献
134.
Sandra Simon Pierre Alcouffe Eliane Espuche 《Journal of Polymer Science.Polymer Physics》2014,52(18):1211-1220
In this study, bimetallic/polymer films are synthesized from polyetherimide (PEI), palladium acetate and silver nitrate for a wide range of total metal amount (from 0 to 30 wt %) and different Ag to Pd molar ratios. Hybrid precursor films are first prepared from polymer/metal complex solutions and the metal nanoparticles are then generated within the PEI matrix by annealing the precursor film under specific conditions. Reference neat PEI films and monometallic films are prepared in the same conditions. Interestingly, formation of AgPd alloys directly within the polymer films is for the first time obtained from a very simple and environmentally friendly route. Based on X‐ray diffraction and transmission electron microscopy analyses, a nanostructuration mechanism is proposed. The interactions of hydrogen towards the nanocomposites are investigated and discussed as a function of the nanoparticle composition. The impact of the nanostructuration is also studied on H2, CO2, and He permeation properties. Significant improvement of barrier properties is achieved. The pertinent parameters of the gas transport are identified and modelled for each gas/composite system. Finally, from both morphological and gas transport analyses, it is concluded that in situ generation AgPd alloys with Pd to Ag ratio above 1 leads to very interesting and promising materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1211–1220 相似文献
135.
136.
M. F. S. Rezende A. M. Lacerda H. -D. Pfannes R. A. Mansur J. D. Ardisson A. I. C. Persiano 《Hyperfine Interactions》1994,83(1):231-234
The effects of filing FeCoV alloys with equiatomic FeCo and up to 14 at% V is studied by Mössbauer spectroscopy and X-ray diffraction. We observed that filing eliminates the paramagnetic component observed in samples in the form of plates. The filed material also presents a linear increase of the lattice parameter and a linear decrease of the average hyperfine field of the alpha phase due to extra low-field satellites with increasing vanadium contents. This indicates that filing produces a gamma to alpha phase transformation, which increases the amount of vanadium in solid solution in the FeCo alpha phase. 相似文献
137.
138.
R. Siquieri J. Rezende J. Kundin H. Emmerich 《The European physical journal. Special topics》2009,177(1):193-205
In this work a study through numerical simulation of dendritic growth for the system Fe-Mn under the influence of a forced
flow field is presented. The investigations are based on an extension of the quantitative phase-field approach developed by
Echebarria et. al. Phy. Rev. E 061604 (2004), to simulate the solidification of Fe-Mn under the influence of a forced flow
field. The simulations are performed for isothermal conditions and the investigation concentrates on the effects of forced
flow on the dendrite morphology during the growth dynamics. The effects of forced flow on microsegregation are also discussed. 相似文献
139.
140.
The contributions that dipolar, single-ion and exchange anisotropy make to the perpendicular susceptibility χ?, the field H′c for which ω↓ (k = 0) vanishes, and other properties of antiferromagnetic MnF2 at T = 0 K are considered, first, i n the ionic approximation. A comparison of the calculated dipolar and single-ion anisotropy with the measured χ?, H′c and magnon dispersion would seemingly require then the inclusion of an unreasonably large anisotropic exchange field HAE = -0.9 kOe. However, an estimate of the effects that overlap and covalency have on the anisotropy reveals that much of the discrepancy between the results obtained from the point-dipolar, ionic approximation and the measured quantities is a consequence of the spatial redictribution of the cation magnetization onto the ligands. 相似文献