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Solvent Ratio (solvent + ratio)
Selected AbstractsPreparation and optimization of 2,4-D loaded cellulose derivatives microspheres by solvent evaporation techniqueJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Z. El Bahri Abstract Controlled release herbicide formulations were prepared by microencapsulation using solvent evaporation technique. 2,4-D was chosen as core material, which was microencapsulated in two cellulose derivatives as matrices: cellulose acetate butyrate butyryl (CAB) and ethylcellulose (EC). The work is intended to produce systems containing the herbicide to reduce its risks by dermal contact, evaporation, or degradation and to control the release of the active agent. The microspheres loaded by 2,4-D were characterized by scanning electron microscopy and infrared spectroscopy. We have obtained microparticles in the range of D32 of 42,277 ,m with CAB and 88,744 ,m with EC by varying the process parameters. The drug entrapment was improved by controlling certain factors such as polymer/solvent ratio, pH of continuous phase, and organic phase solvent. The drug release was established in deionized water at pH = 5.5 and 25°C and the 2,4-D concentrations were estimated by UV analysis. The release data were analyzed according to Fick's law and the results demonstrate that the release rate can be controlled by modifying the process parameters. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2742,2751, 2007 [source] Fast determination of prominent carotenoids in tomato fruits by CEC using methacrylate ester-based monolithic columnsELECTROPHORESIS, Issue 22 2007Ana Maria Adalid Abstract In this study, the major carotenoids (,-carotene and lycopene) present in tomato fruits were analyzed by CEC with a methacrylate ester-based monolithic column. The effects of the porogenic solvent ratio, and the hydrophobicity of bulk monomer employed were examined on carotenoids separations. A fast separation of these analytes was achieved in less than 5.0,min in a mobile phase containing 35% THF, 30% ACN, 30% methanol, and 5% of a 5,mM Tris aqueous buffer, pH,8, with lauryl methacrylate-based monoliths. The CEC method was evaluated in terms of detection limit and reproducibility (retention time, area, and column preparation) with values below 1.6,,g/mL and 7.2%, respectively. The proposed procedure was successfully applied to the determination of both carotenoids in fruits of several tomato-related species and its usefulness to analyze large series of samples for nutritional quality screening trials in tomato breeding programs is demonstrated. To our knowledge, this is the first work that exploits the powerful and user-friendly monolithic technology for quality breeding and germplasm evaluation program purposes. [source] Polymer Scaffolds for Small-Diameter Vascular Tissue EngineeringADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Haiyun Ma Abstract To better engineer small-diameter blood vessels, a few types of novel scaffolds are fabricated from biodegradable poly(L -lactic acid) (PLLA) by means of thermally induced phase-separation (TIPS) techniques. By utilizing the differences in thermal conductivities of the mold materials and using benzene as the solvent scaffolds with oriented gradient microtubular structures in the axial or radial direction can be created. The porosity, tubular size, and the orientational direction of the microtubules can be controlled by the polymer concentration, the TIPS temperature, and by utilizing materials of different thermal conductivities. These gradient microtubular structures facilitate cell seeding and mass transfer for cell growth and function. Nanofibrous scaffolds with an oriented and interconnected microtubular pore network are also developed by a one-step TIPS method using a benzene/tetrahydrofuran mixture as the solvent without the need for porogen materials. The structural features of such scaffolds can be conveniently adjusted by varying the solvent ratio, phase-separation temperature, and polymer concentration to mimic the nanofibrous features of an extracellular matrix. These scaffolds were fabricated for the tissue engineering of small-diameter blood vessels by utilizing their advantageous structural features to facilitate blood-vessel regeneration. [source] Supercritical carbon dioxide separation of bergamot essential oil by a countercurrent processFLAVOUR AND FRAGRANCE JOURNAL, Issue 5 2003Marco Poiana Abstract The ef,ciency of separation of bergamot essential oil, performed by a countercurrent column ,lled with Raschig rings and using supercritical carbon dioxide as partition solvent, is affected by various parameters. In the experiments explained in this work, the direct effect of CO2 density was shown and the ratio between the amount of oil loaded to on the column and the amount of CO2 used were discussed. The conditions that produced extracts with a similar volatile fraction composition of starting material and with a high yield (more than 80% of recovery) were those with a low feed:solvent ratio; the lowest bergaptene content was obtained at low CO2 density or at high feed:solvent ratio. A good result was observed at a CO2 density of 206 g/dm3 (8 MPa of pressure and a temperature gradient of 46,50,54 °C) and a feed:solvent ratio of 9.4,9.6; in this separation, a yield of 74,77% and a bergaptene content lower than 0.01% was measured. Copyright © 2003 John Wiley & Sons, Ltd. [source] The application of response surface methodology to the production of phenolic extracts of lemon grass, galangal, holy basil and rosemaryINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 2 2006T. Juntachote Summary The effects of independent variables (ethanol:water ratio, temperature and time) on the extraction yield and antioxidant properties of phenolic extracts from lemon grass, galangal, holy basil and rosemary were studied. The extraction solvent ratio of ethanol to water was found to have a significant (P < 0.05) influence on extraction yield, reducing power and total phenolic content, but not on the antioxidant activity of all herb and spice samples, while extraction temperature had only minor effects. Extraction time had a significant (P < 0.05) effect only on the reducing power of holy basil extracts. The optimum extraction conditions, i.e. extraction solvent ratio of ethanol to water, extraction temperature and extraction time for maximum total phenolic content, were 3:1 at 25 °C for 30 min for lemon grass, 3:1 at 75 °C for 90 min for galangal and holy basil and 3:1 at 75 °C for 30 min for rosemary. [source] Single-Mode Microwave Ovens as New Reaction Devices: Accelerating the Living Polymerization of 2-Ethyl-2-OxazolineMACROMOLECULAR RAPID COMMUNICATIONS, Issue 22 2004Frank Wiesbrock Abstract Summary: The ring-opening cationic polymerization of 2-ethyl-2-oxazoline was performed in a single-mode microwave reactor as the first example of a microwave-assisted living polymerization. The observed increase in reaction rates by a factor of 350 (6 h,,,1 min) in the range from 80 to 190,°C could be attributed solely to a temperature effect as was clearly shown by control experiments and the determined activation energy. Because of the homogenous microwave irradiation, the polymerization could be performed in bulk or with drastically reduced solvent ratios (green chemistry). Monomer conversion, represented by the ratio ln{[M0]/[Mt]}, plotted against time for six temperatures in the range from 80 to 180,°C, and polymerization reaction vials, showing an increase in yellow color for those reactions performed (well) above and below 140,°C, indicating side reactions. [source] Simple Bisthiocarbonohydrazones as Sensitive, Selective, Colorimetric, and Switch-On Fluorescent Chemosensors for Fluoride AnionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2007Feng Han Abstract Bisthiocarbonohydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F,) or acetate (Ac,). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the ,-conjugation framework, the delocalization bridge CHN, the aromatic moiety, and the hetero atom in the CX group (X=O, S) of the sensors. Single-crystal structures and 1H,NMR titration analysis shows that the CHN moiety is a hydrogen-bond donor, and it is proposed that an additional CH,,,F hydrogen bond is formed for the sensors in the presence F,. A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F, and Ac,. The recognition of F, in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H2O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor,F, complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN. [source] | |||||||||||||