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81.
Luiz A. F. Coelho Jos V. Oliveira Saul G. D'vila Janete H. Y. Vilegas Fernando M. Lanas 《Journal of separation science》1997,20(8):431-436
The effects of temperature and solvent density on the characteristics of the extracts obtained from supercritical fluid extraction (SFE) of the volatile compounds from Brazilian rosemary (Rosamarinus officianalis L., Labiatae) using carbon dioxide (CO2) as solvent were investigated. The experiments were performed in a semi-batch laboratory scale home-made unit at two temperatures, viz. 310.15 and 320.15 K, over the pressure range of 100-160 bar. This study allowed to determine the crossover point and the maximum solubility of the oil. The products were analyzed by HRGC-MS, and compounds grouped in three different classes according to their molecular mass distribution in order to evaluate the influence of the variables studied on the characteristics of the extracts. The model proposed by Sovová was adopted in an attempt to interpret the mass transfer phenomena in the extraction process. 相似文献
82.
Commercial solid-phase extraction (SPE) cartridges with C18 bonded silica packings effectively cleaned up acetonitrile extracts of 3-g samples of fats and oils for determination of organophosphorus pesticide residues by gas chromatography with flame photometric detection. Cartridges from three different sources were tested and found to differ in lipid capacity and inertness (free silanol activity). Consequently, the amount of packing (i.e., number of cartridges) and/or the choice of eluent used were adjusted for each brand of cartridge to achieve optimum clean-up and analyte recovery. Seven pesticides with a wide range of polarity (acephate, azodrin, chlorpyrifos, diazinon, malathion, methamidophos and methyl parathion) were separated from coextracted lipids by elution with either acetonitrile or methanol, depending on the brand of cartridge used. Cartridges were regenerated by purging lipids with dichloromethane and were reused numerous times without apparent loss of effectiveness. Recoveries from vegetable oils and butterfat fortified with the seven compounds at levels of 0.05–0.87 μg g?1 ranged from 80 to 103%. Practical limits of determination range from 0.01 to 0.08 μg g?1, depending on analyte response. 相似文献
83.
Alex von Bohlen Henriette Brink-Kloke Christiane Althoff 《Analytica chimica acta》2003,480(2):327-335
An aqua regia extraction procedure for heavy metals in soils optimised for total reflection X-ray fluorescence analysis is presented. The procedure is applied to 92 soil samples of medieval layers from the city area of Dortmund. Sixteen elements (P, S, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Ag, Sn, and Pb) were used to characterise 17 sample sites. The results are projected onto the medieval urban structure of Dortmund. Two sites loaded with non-ferrous heavy metal could be detected and correlated with archaeological data. The efficiency and repeatability of the proposed extraction procedure is discussed. 相似文献
84.
E. Lachowicz B. R
a
ska F. Teixidor H. Meliani M. Barboiu N. Hovnanian 《Journal of membrane science》2002,210(2):279-290
The reactivity of new ligands described as S1, S5, S2O9 (in respect to character and amount of donors) towards metal ions was examined by extraction from HNO3 and HCl media. These ligands were next utilised as carriers for Ag and Pd transport through a supported liquid membrane (SLM). The effect of collecting a greater number of S donors in one molecule and the influence of type of donors (O–S versus S) on efficiency and selectivity of Ag and Pd(II) extraction and transport were examined.
The extraction of Ag from HNO3 solutions increased with increasing amount of S-donors in one molecule (S12O95). For palladium the sequence was different (S512O9). The transport of Ag through SLM impregnated with m-chlorotoluene solution of ionophore increased in the same order as in the case of extraction, whereas for Pd the row was different: S52O91. The highest fluxes of Ag and Pd transported from HNO3 equalled to 5.25×10−7 and 1.37×10−7 mol/m2 s, respectively. Palladium flux depended on stripping solution type (Na2S2O3
85.
G. Durand S. Chiron V. Bouvot D. Barceló 《International journal of environmental analytical chemistry》2013,93(1-2):31-42
Abstract C-18 Empore extraction disks were used for the isolation and trace enrichment of different groups of pesticides from river water and artificial sea water at concentration levels of 0.2, 5 and 20 μg/l [chlorotriazines, (atrazine and simazine), their dealkylated metabolites, (deethyl- and deisopropylatrazine), organophosphorus (parathion-ethyl), phenylurea (linuron), anilide (propanil), carbamate (aldicarb and carbofuran) and carbamate transformation products (aldicarb sulfoxide, aldicarb sulfone and 3-hydroxy-7-phenol carbofuran]. The extraction disks allowed high flow rates thus 51 samples could be processed within 2h. 30 min. For most of the pesticides the recoveries, as determined by liquid chromatography with diode array detection (LC-DAD), varied from 74 up to 125% with coefficients of variations (CV) of 5-10%, whereas for the carbamate transformation products the recoveries were in the range of 30-35% having a CV of 17-21%. At spiking level of 0.2 μg/l the dealkylated triazine metabolites and the carbamate transformation products were not detected at all. 相似文献
86.
Literature data on distribution ratios (Dw) of Np(V) and Pa(V) for the AG1-X8 resin are scarce whereas those related on resin capacity factors (k′) values for TEVA, TRU and U/TEVA resins are absent. Therefore, batch extraction experiments for Pa(V) and Np(V) from HCl and HNO3 media were realized, at tracer scale, with AG1-X8 and EIChroM resins (TEVA, TRU and U/TEVA). Based on the new Dw and k′ values obtained in this study, a new protocol for Pa/Np separation has been developed leading to a better separation factor of 105 and a chemical yield of 97 ± 3% and 99 ± 1% for Pa and Np, respectively. A separation of 231Pa from uranium matrix was successfully tested. 相似文献
87.
Bound rubber formation was investigated in detail by applying various extraction temperatures (at room temperature, 90°C, and 180°C) and novel treatment methods (ammonia bubbling and sonication). Bound rubbers could be divided into three major components of core shell, primary layer including tightly primary layer and occluded rubber, and secondary layer including connecting filament. Bound rubber content of the core shell was measured by four successive procedures of extraction at room temperature, ammonia bubbling, extraction at 180°C and sonication. Bound rubber content of the tightly primary layer was measured by three successive procedures of extraction at 90°C, ammonia bubbling and sonication. Bound rubber content of the primary layer was measured by two successive procedures of extraction at 90°C and sonication. 相似文献
88.
The fast transient fluorescence (FTRF) technique was used to study critical exponents at the glass transition in free-radical crosslinking copolymerization (FCC) for two different monomeric systems, methyl methacrylate (MMA) and styrene (S). Pyrene (Py ) was used as a fluorescence probe. The fluorescence lifetimes of Py from its decay traces were measured and used to monitor the gelation process. Changes in the viscosity of the pregel solutions due to glass formation dramatically enhance the fluorescent yield of aromatic molecules. This effect is used to study the glass transition upon gelation of MMA and S monomeric systems as a function of time, at various temperatures and crosslinker concentrations. The results are interpreted in the view of percolation theory. The gel fraction and weight average degree of polymerization exponents β and γ are found to be 0.37 ± 0.02 and 1.66 ± 0.07 in agreement with percolation results. 相似文献
89.
《Analytical letters》2012,45(12):995-1001
Abstract Correlations between extraction distribution ratios, bond types, and common solvent physical properties were determined for 19 extraction systems. Different types of bonding are involved in the water adduct formation on different types of chelates. 相似文献
90.
《Comptes Rendus Chimie》2014,17(3):261-267
Solvent extraction processes have been largely used in various industries. They recently were improved through new physical concepts such as CO2 Supercritical Fluid Extraction, Ultrasound assisted process, Microwave-assisted extraction, Instant Controlled Pressure Drop DIC-assisted extraction… Systematically, a pretreatment stage of grinding takes place in order to improve the exchange surface increasing the starting accessibility. Swelling of the material structure implies an increase of the porosity thus leading to higher solvent diffusivity within the solid matrix. A new concept of expanded granule powder has recently been defined using Instant Controlled Pressure Drop DIC technology. Whatever the type of solvent is (even CO2-SFE), such a swelled structure dramatically intensifies the kinetics through a higher specific exchange surface thanks to the open pores, while improving the solution solvent–solute diffusivity within the solid. Coupled to ultrasound, the internal transfer of solute within the pore solvent can likewise be intensified by replacing molecular diffusion within the pores by an effective convection transfer. In this work, we carried out a first approach of modeling of solvent extraction kinetics of expanded granules involving higher exchange surface and greater internal diffusion process. 相似文献