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Preparation Procedure (preparation + procedure)
Kinds of Preparation Procedure Selected AbstractsRole of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Yuxia Luan Dr. Abstract Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed. [source] The Effect of Preparation Procedures on the Morphology of Melanin from the Ink Sac of Sepia officinalisPIGMENT CELL & MELANOMA RESEARCH, Issue 1 2003Yan Liu The structure of melanin extracted from the ink sac of the cuttlefish Sepia officinalis was examined for different methods of isolation and purification of the pigment. Scanning electron microscopy (SEM) images of Sepia eumelanin prepared by different procedures establish that multi-,m-sized aggregates reported by previous workers are generated by their sample preparation, and that the dominant constituents of Sepia melanin are ,150 nm spherical granules. Brunauer-Emmett-Teller (BET) measurements reveal that Sepia eumelanin from Sigma (prepared by spray drying the pigment) has a surface area of 14.3 m2/g. Pigment extracted directly from the fresh ink sac and then freeze-dried has a surface area of 21.5 m2/g, while CO2 -supercritically dried has a surface area of 37.5 m2/g. This is consistent with SEM images showing that the process of freeze-drying produces aggregates, but to a lesser extent than spray drying. Supercritical drying of the sample produces suspensions of the individual ,150 nm granule, which is more reflective of the natural pigment. Brunauer-Emmett-Teller surface area analysis and Barrett-Joyner-Halenda (BJH) pore volume analysis indicate that the surface of the granules is not smooth and the interior of the granules is not porous, but rather the aggregates of granules are porous. Ultra-high resolution SEM and atomic force microscopy (AFM) images show the granules are easily deformed and are comprised of smaller constituents. De-aggregation of the granules by sonication and ultra-filtration reveal a range of structures depending on the pore size of the membrane used. The implications of these results on quantifying photochemical properties and kinetic reaction rate constants of melanin are discussed. [source] Thermal Behavior of Isotactic Poly(propylene)/Maleated Poly(propylene) BlendsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2007Catalin Vîlcu Abstract This paper analyzes the thermal and thermo-oxidative degradation behavior, phase separation, melting, and crystallization of blends consisting of isotactic poly(propylene) (IPP) and poly(propylene) grafted with maleic anhydride (PP- g -MA). It has been established that, depending on the blend composition and crystallization/preparation procedure, the blends of IPP and PP- g -MA can either co-crystallize or evidence phase separation. This conclusion has been attained by comparing the DSC results of crystallization under dynamic and isothermal conditions with X-ray diffraction results. On the basis of the obtained results, the optimum mixing ratios have been established as 95,85 wt.-% IPP/5,15 wt.-% PP- g -MA. Thermo-oxidative behavior has been studied by thermogravimetry and differential thermal analysis. [source] Growth and characterization of Nd, Yb , yttrium oxide nanopowders obtained by sol-gel methodCRYSTAL RESEARCH AND TECHNOLOGY, Issue 12 2007A. Rzepka Abstract Nanopowders of Y2O3 pure, doped and codoped by Nd3+, Yb3+ were obtained by sol-gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one-phased compounds of Y2O3 doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y2O3 doped 0.5 at% Nd and 2 at% Yb are presented. Y2O3 containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co-doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Amperometric Glucose Biosensors Based on Glassy Carbon and SWCNT-Modified Glassy Carbon ElectrodesELECTROANALYSIS, Issue 1 2008Irene Carpani Abstract Different carbonaceous materials, such as single-walled carbon nanotubes (SWCNTs) and glassy carbon submitted to an electrochemical activation at +1.80,V (vs. SCE) for 900,s, have been used with the aim of comparing their performances in the development of enzyme electrodes. Commercial SWCNTs have been pretreated with 2.2,M HNO3 for 20,h prior to use. The utility of activated GC as promising material for amperometric oxidase-based biosensors has been confirmed. With glucose oxidase (GOx) as a model enzyme, glucose was efficiently detected up to 1 mM without the use of a mediator. Both electrodes operated in stirred solutions of 0.1,M phosphate buffer (pH,5.5), containing dissolved oxygen, at a potential of ,0.40,V vs. SCE. Although the performances of the two carbonaceous materials were comparable, the biosensors based on activated GC were characterized by a practically unchanged response 40 days after the fabrication, a better signal to noise ratio, and a little worse sensitivity. In addition, the preparation procedure of such biosensors was more simple, rapid and reproducible. [source] Microstructural Characterization of Lamellar Features in TiAl by FIB Imaging,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Dennis Peter A novel experimental procedure is introduced to determine phase fractions and the distribution of individual phases of TiAl-based two-phase alloys using the focused ion beam (FIB) technique. Two , -titanium aluminide alloys with a fine-grained duplex and a nearly lamellar microstructure are examined. The special FIB-based preparation procedure results in high contrast ion beam-induced images for all investigated alloys and allows to quantify the phase contents easily by automated microstructural analysis. Fine two-phase structures, e.g. lamellar colonies in , -TiAl, can be imaged in high resolution with respect to different phases. To validate the FIB-derived data, we compare them to results obtained with another method to determine phase fractions, electron back-scatter diffraction (EBSD). This direct comparison shows that the FIB-based technique generally provides slightly higher ,2 -fractions, and thus helps to overcome the limited lateral resolution near grain boundaries and interfaces associated with the conventional EBSD approach. Our study demonstrates that the FIB-based technique is a simple, fast, and more exact way to determine high resolution microstructural characteristics with respect to different phase constitutions in two-phase TiAl alloys and other such materials with fine, lamellar microstructures. [source] Adhesion Characteristics of PDMS Surfaces During Repeated Pull-Off Force Measurements,ADVANCED ENGINEERING MATERIALS, Issue 5 2010Elmar Kroner Abstract To mimic the adhesive effects of gecko toes, artificial surfaces have been manufactured recently using polydimethylsiloxanes (PDMS). However, the effects of repeated contacts on the adhesive properties remain largely unexplored. In this paper we report on the effect of repeated pull-off force measurements on the adhesion behavior of PDMS (polymer kit Sylgard 184, Dow Corning) tested with a borosilicate glass probe. A decrease in pull-off force with increase in number of test cycles is found until a plateau is reached. The initial value and the rate of change in pull-off force strongly depend on the sample preparation procedure, including curing time and cross-linking. It is proposed that the behavior is due to steady coverage of the probe with free oligomers. The results are crucial for developing reusable, durable, and residue-free bioinspired adhesives. [source] Low-Temperature and High-Strain Rate Superplastic ZirconiaADVANCED ENGINEERING MATERIALS, Issue 3 2003Y. Sakka A superplastic ceramic with a strain rate comparable to metals based on 3% Y2O3 -doped tetragonal zirconia (3YTZ) was synthesized at relatively low temperature, based on the doping with MgO and TiO2. The desirable material properties result from both a refined preparation procedure for the zirconia, and from enhanced cation lattice diffusion due to the MgO and TiO2 doping. [source] Direct integration of cell-free-synthesized connexin-43 into liposomes and hemichannel formationFEBS JOURNAL, Issue 16 2010Yuki Moritani Proteoliposomes were directly prepared by synthesizing membrane proteins with the use of minimal protein synthesis factors isolated from Escherichia coli (the PURE system) in the presence of liposomes. Connexin-43 (Cx43), which is a water-insoluble integral membrane protein that forms a hexameric complex in membranes, was cotranslationally integrated with an essentially uniform orientation in liposomes. The addition of liposomes following protein expression (post-translational presence of liposomes) did not lead to the integration of Cx43 into the liposome membranes. The amount of integrated Cx43 increased as the liposome concentration increased. The presence of liposomes did not influence the total amount of synthesized Cx43. The Cx43 integrated into the liposome membranes formed open membrane pores. These results indicate that the liposomes act in a chaperone-like manner by preventing Cx43 from aggregating in solution, because of integration into the bilayer, and also by functionalization of the integrated Cx43 in the membrane. This is the first report that cell-free-synthesized water-insoluble membrane protein is directly integrated with a uniform orientation as a functional oligomer into liposome membranes. This simple proteoliposome preparation procedure should be a valuable approach for structural and functional studies of membrane proteins. Structured digital abstract ,,MINT-7900670: Cx-43 (uniprotkb:P08050) and Cx-43 (uniprotkb:P08050) bind (MI:0407) by cross-linking study (MI:0030) [source] Radiation Grafted Membranes for Polymer Electrolyte Fuel Cells,FUEL CELLS, Issue 3 2005L. Gubler Abstract The cost of polymer electrolyte fuel cell (PEFC) components is crucial to the commercial viability of the technology. Proton exchange membranes fabricated via the method of radiation grafting offer a cost-competitive option, because starting materials are inexpensive commodity products and the preparation procedure is based on established industrial processes. Radiation grafted membranes have been used with commercial success in membrane separation technology. This review focuses on the application of radiation grafted membranes in fuel cells, in particular the identification of fuel cell relevant membrane properties, aspects of membrane electrode assembly (MEA) fabrication, electrochemical performance and durability obtained in cell or stack tests, and investigation of failure modes and post mortem analysis. The application in hydrogen and methanol fuelled cells is treated separately. Optimized styrene,/,crosslinker grafted and sulfonated membranes show performance comparable to perfluorinated membranes. Some properties, such as methanol permeability, can be tailored to be superior. Durability of several thousand hours at practical operating conditions has been demonstrated. Alternative styrene derived monomers with higher chemical stability offer the prospect of enhanced durability or higher operating temperature. [source] Direct Current Plasma Emission Spectrometric Determination of Major, Minor and Trace Elements in Microwave Oven Acid Leachates of Powdered Whole Coal SamplesGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005Sandro Fadda DCP-AES; échantillons de charbon; four à micro-ondes; éléments facilement ionisables; effets de matrice. Major concentrations of Al2O3, Fe2O3, MgO, CaO, Na2O and K2O, minor levels of TiO2, P2O5 and thirty petrologically, geochemically and environmentally significant trace elements have been determined in microwave oven acid leachates of whole powdered coal samples by direct current plasma-atomic emission spectrometry (DCP-AES). A single sample preparation procedure was suitable for all the determinations with no additional dilution step for major elements solution. Dried samples (0.5 g) were treated in low-pressure PFA digestion vessels with HF/HCl/HNO3/HClO4 acids to quantitatively extract the analytes from the bulk material, while leaving the major part of organic matrix as a residue. The major constituents of geological samples, in particular the easily ionised elements (EIEs) such as alkali and alkaline earths, may complicate the instrumental determinations in DCP-AES because of differential enhancements of elemental emission intensities and stray light interferences. Taking account of these factors, the coal matrix is considered to have very low major oxide totals as compared to many other common geo-environmental and related materials (rocks, sediments, soil, ashes etc.). The sample size employed here, while yielding a relatively concentrated solution to cover a wide range of elemental determinations, provided a sample matrix that significantly diminished interferences for DCP measurements. The need for closely matching the unknowns and calibrators was eliminated except for overall acidity and an excess quantity of caesium for EIE buffering. Calibration of the spectrometer was accomplished by simple aqueous single element solutions as high concentration calibrators in addition to a reagent blank as a low concentration calibrator. Two point working curves were established to allow for the maximum concentrations of each element expected in the unknowns. The precision of determinations under routine conditions as well as the reproducibility of the leaching and precision of instrumental measurements have been evaluated. Relative standard deviations (RSD) were of 1,2% for those elements whose concentrations in solid samples were well above the limits of quantification. Method detection limits in the buffered solutions were also evaluated. To evaluate the accuracy of the microwave oven-DCP method a suite of eight certified coal reference materials of differing rank, were analysed with good agreement with the certified and/or available published data. Results are presented for the uncertified major oxides in the AR series reference materials. Les concentrations en éléments majeurs: Al2O3, Fe2O3, MgO, CaO, Na2O et K2O, en éléments mineurs TiO2, P2O5 et en 30 éléments en trace dont le comportement est important en Pétrologie, en Géochimie et en Environnement, ont été analysées par spectrométrie d'émission atomique à plasma à courant direct (DCP-AES), dans des lessivages acides effectués dans un four à micro-ondes sur des échantillons de charbon mis en poudre. Ce mode préparatoire unique est adaptéà toutes les déterminations sans qu'il soit nécessaire d'effectuer une dilution supplémentaire pour l'analyse des éléments majeurs. Les échantillons préalablement desséchés (0.5 g) sont traités dans les pots de PFA de basse pression, avec un mélange d'acides HF/HCl/HNO3/HClO4, afin d'extraire quantitativement les analytes du matériel géologique, tout en laissant la plus grande part de la matrice organique sous forme résiduelle. Les constituants majeurs de ces échantillons géologiques, en particulier les éléments facilement ionisables (EIEs) tels que les alcalins et les alcalino-terreux, peuvent compliquer l'analyse en DCP-AES à cause des rendements variables des intensités d'émission élémentaires et des interférences de raies de lumière. Mais là dessus, la matrice de charbon se révèle être bien plus pauvre en oxydes majeurs que les autres matériaux géologiques, environnementaux ou de type proche (roches, sédiments, sols, cendres). La taille d'échantillon retenue ici, tout en fournissant une solution relativement concentrée qui permet la détermination de beaucoup d'éléments, fournit une matrice qui diminue significativement les interférences lors de la mesure par DCP-AES. Le besoin d'avoir les solutions d'échantillons et les solutions de calibration avec des matrices très proches est donc éliminé, mis à part pour l'acidité totale et la quantité excessive de Césium pour tamponner les EIE. La calibration du spectromètre est faite avec des solutions mono- élémentaires aqueuses, pour déterminer les points de concentrations élevées et avec le blanc de réactifs pour le point de concentration basse. Les courbes de calibrations sont déterminées avec 2 points, pour autoriser l'analyse de concentrations maximales pour chaque élément dans les échantillons inconnus. La précision des déterminations en conditions de routine ainsi que la reproductibilité de l'opération de lessivage et la précision instrumentale des analyses ont étéévaluées. Les déviations standards relatives (RSD) sont de 1,2% pour tout élément dont les concentrations dans le solide sont au dessus des limites de quantification. Les limites de détection de la méthode dans les solutions tamponnées ont aussi étéévaluées. Enfin, pour évaluer la justesse de cette méthode "micro-ondes - DCP" huit charbons certifiés matériaux de référence de différents types ont été analysés, et sont en bon accord avec les données certifiées ou seulement disponibles publiées. Les données sur un certain nombre d'oxydes d'éléments majeurs actuellement non certifiés sont présentées pour les matériaux de référence AR. [source] Combining microwave and ultrasound irradiation for rapid synthesis of nanowires: a case study on Pb(OH)BrJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 12 2009Xiao-Fang Shen Abstract BACKGROUND: One-dimensional (1D) nanostructures such as wires, tubes and belts have attracted much attention in recent years because of their fascinating properties and promising applications, and various methods have been developed to prepare 1D nanostructures. Microwave and ultrasound, two methodologies for rapid synthesis, have both been applied to fabricate nanostructures. This paper reports on combining microwave and ultrasound irradiation as a new strategy for rapid synthesis of nanowires. Using Pb(OH)Br as a study case, nanowires were rapidly synthesized under the combined irradiation. The use of the ionic liquid 1-butyl-3-methylimidazolium bromide as a structure-directing agent and microwave absorbent significantly simplified the preparation procedure. RESULTS: Combined microwave,ultrasound irradiation at (50 W,50 W) greatly reduced the reaction time (10 min) and significantly increased the product yield (45.0%) in comparison with conventional heating (24 h reaction time, 23.0% yield). Combined microwave,ultrasound irradiation at (50 W,50 W) also changed the resultant wires from 20,30 µm diameter and 2,3 mm long to 80,800 nm and 50,100 µm, respectively. Further increase in power of the combined irradiation (250 W,50 W) led to a dramatic reduction in the reaction time (80 s) with a slightly increased yield of 48.2%. CONCLUSIONS: The obvious advantages of combined microwave,ultrasound irradiation are marked improvement of the product yield, significant enhancement of reaction rate and increased aspect ratio of the 1D structure. Copyright © 2009 Society of Chemical Industry [source] Mandibular and maxillary furcation tunnel preparations , literature review and a case reportJOURNAL OF CLINICAL PERIODONTOLOGY, Issue 1 2001Stefan G. Rüdiger Abstract Aim: The objective of this literature review and subsequent case report is to discuss and illustrate the tunnel preparation procedure as a treatment alternative for furcation-involved molars. Review of the literature: Furcation tunnel preparation, i.e., the creation of access for plaque control between periodontally diseased roots, has not been discussed in the literature as comprehensively as root resective therapy, though success rates appear to fall within the same range. A short root trunk and a wide furcation entrance diameter are prerequisites for the indication of the tunnel preparation procedure. Although accessory canals in the furcation area are frequent findings on extracted teeth, endodontic complications have not been reported to be major complications after tunnel preparation. Caries developed at tunneled teeth even under proper maintenance, but did not necessarily lead to the loss of an affected tooth. Case report: In the case presented to illustrate the indication for the tunnel preparation procedure, periodontal disease was almost entirely restricted to the furcation sites of molar teeth. Affected teeth were either extracted or left intact and subjected to tunneling procedures. Periodontal health could be established and maintained at both single and double tunnels over a period of 2 years of periodontal supportive therapy. [source] On the nature of Ti(IV)-pillared layered metal hydroxides prepared from green, water-soluble Ti-peroxideAICHE JOURNAL, Issue 5 2010Jing He Abstract Ti-peroxide pillared layered double hydroxides (LDHs) have been prepared for the first time using water-soluble Ti-peroxide as an intercalating precursor. It is novel and alluring that the whole preparation procedure does not involve any usage of organic or chlorine-containing hazards. Intercalated into the LDH interlayer region, Ti-peroxide is prevented partially from condensation in the solvent evaporation. The interlayer TiO2 unit exists in triangular (,2) structure with C2, symmetry in most cases, giving an interlayer gallery of 0.50,0.60 nm. But in the case of pH 4.0, monodentate (,1) structure is also observed, giving an interlayer gallery of 0.70 nm. All the Ti-peroxide pillared LDHs prepared in this work show catalytic activity in the selective oxidation of thioether. The Ti-peroxide introduced into the interlayer regions of Mg/Al LDH with a particle size of around 50,120 nm exhibits better recyclability than Ti-peroxide gel, either in bulk or adsorbed on the exterior surface of LDH particles. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Determination of BAPTA-AM, the acetoxymethyl tetraester of BAPTA, in rat plasma by liquid chromatography tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2006Feng Zheng Abstract BAPTA-AM is the acetoxymethylester of the calcium chelator BAPTA and has demonstrated efficacy in several animal models of cerebral ischemia. This paper describes the development of a method for the determination of BAPTA-AM in rat plasma by liquid chromatography/tandem mass spectrometry. Owing to multiple ester groups in the structure of BAPTA-AM, [M + Na]+ was chosen as the analytical ion for quantification of BAPTA-AM. During the analytical method development, a high percentage of organic solvent and the addition of an amount of sodium acetate and formic acid in the mobile phase were found to favor the sensitivity and reproducibility of [M + Na]+. Poor fragmentation was usually observed in the MS/MS spectra of sodium adduct ions. However, abundant and reproducible fragment ions were observed for the BAPTA-AM sodium adduct ion, and therefore the traditional selective reaction-monitoring mode was used to further improve the sensitivity of MS detection. Because of the lability of the ester bond, a combination of fluoride and hydrochloric acid was applied to minimize the enzymatic hydrolysis, and acetonitrile was chosen to avoid the chemical hydrolysis or solvolysis during the sample collection and preparation procedure. On the basis of these studies, a rapid, sensitive and reproducible method for the determination of BAPTA-AM in rat plasma, using LC/ESI-MS/MS and a simple protein precipitation procedure, was developed and validated. Also, the present method was successfully applied to the determination of BAPTA-AM plasma concentrations for pharmacokinetic studies in rats. Copyright © 2006 John Wiley & Sons, Ltd. [source] DEVELOPMENT OF SAMPLE PREPARATION, PRESENTATION PROCEDURE AND SENSORY DESCRIPTIVE ANALYSIS OF GREEN TEAJOURNAL OF SENSORY STUDIES, Issue 4 2008SOH MIN LEE ABSTRACT Although the infusing condition of green tea is critical in determining green tea quality, the green tea industries lack a validated standardized tea preparation procedure. The objectives were (1) to develop an effective sample preparation and presentation procedure to conduct an objective sensory analysis; and (2) to elucidate the effects of green tea types and infusing conditions on the sensory characteristics of green tea. The optimum infusing times for green tea at two temperatures (60 and 80C) were determined using the just-about-right scale evaluated by consumers. Then, a descriptive analysis was conducted. The panelists developed 16 descriptors, and determined the reference samples and the tasting procedure. The optimum infusing time,temperature combinations are approximately 3 min at 60C or 1 min at 80C. The intensity of fermented-like flavor increased, but cut grass and floral flavor decreased with the lower-graded tea leaf. Samples infused at 60C,3 min were sweeter but less bitter than samples at 80C,1 min. PRACTICAL APPLICATIONS The sample preparation method and evaluating conditions developed in this study have been validated using both analytical and consumer studies. The protocols showed to be powerful in discriminating the sensory characteristics between the samples when conducting objective sensory analyses. The sensory lexicons and standards established should be useful to researchers and product developers who are working with flavors of green tea. Additionally, the sample preparation method and evaluation procedure introduced in this study are relatively straightforward, thus, making it possible for the general sensory scientist group to use an effective standardized method when conducting objective sensory analyses of green tea. [source] Supported liquid membranes in hollow fiber liquid-phase microextraction (LPME) , Practical considerations in the three-phase modeJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2007Kari Folde Bårdstu Abstract In this work, three-phase liquid-phase microextraction (LPME) based on a supported liquid membrane (SLM) sustained in the wall of a hollow fiber was investigated with special focus on optimization of the experimental procedures in terms of recovery and repeatability. Recovery data for doxepin, amitriptyline, clomipramine, and mianserin were in the range of 67.8,79.8%. Within-day repeatability data for the four basic drugs were in the range of 4.1,7.7%. No single factor was found to be responsible for these variations, and the variability was caused by several factors related to the LPME extractions as well as to the final HPLC determination. Although the volume of the SLM varied within 0.4,3.1% RSD depending on the preparation procedure, and the volume of the acceptor solution varied within 4.8% RSD, both recoveries and repeatability were found to be relative insensitive to these variations. Thus, the handling of microliters of liquid in LPME was not a very critical factor, and the preparation of the SLM was accomplished in several different ways with comparable performance. Reuse of hollow fibers was found to suffer from matrix effects due to built-up of analytes in the SLM, whereas washing of the hollow fibers in acetone was beneficial in terms of recovery, especially for the extraction of the most hydrophobic substances. Several of the organic solvents used in the literature as SLM suffered from poor long-term stability, but silicone oil AR 20 (polyphenyl-methylsiloxane), 2-nitrophenyl octyl ether (NPOE), and dodecyl acetate (DDA) all extracted with unaltered performance even after 60 days of storage at room temperature. [source] Self-organization and finite size effects in epitaxial ferromagnetic MnAs films on GaAsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2007L. Däweritz Abstract The self-organized striped structure of coexisting ,-MnAs and ,-MnAs, characteristic for MnAs films grown on GaAs(001) by molecular beam epitaxy under As-rich conditions at low temperature, has been studied in samples prepared under conditions closer to the equilibrium. Whereas the period of the stripe pattern is independent on the preparation procedure, the width of the ferromagnetic ,-MnAs stripes increases. Thus, the aspect ratio p between the stripe width L and the stripe thickness t can be varied over a wide range. The magnetic properties of the finite-size magnetic system are investigated as a function of the ratio p at room temperature. The transition from type-I domains with meander-like contrast in the magnetic force microscopy (MFM) image to type-II domains with a line-shaped contrast due to the division of the stripe into N subdomains across the stripe occurs at p ratios expected from a model based on the shape anisotropy. Besides the well-known N = 3 type-II domains also type-II domains with N = 4, 5 were detected. When the stripe width approaches the period of the self-organized structure, the boundary between two neighboring stripes is imaged as chessboard-like contrast in the MFM pattern. The shape of the magnetic hysteresis loops changes with the p ratio or, in other words, with the predominance of in-plane or out-of plane magnetic moments in the demagnetized state. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conducting and transparent SWNT/polymer compositesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006Urszula Dettlaff-Weglikowska Abstract Flexible, transparent and conducting poly(methyl methacrylate) (PMMA) composites films were prepared using SOCl2 functionalized SWNTs. Optical absorption spectra measured on composite films confirm that the composite preparation procedure preserves the electronic properties (position of the Fermi level) of the p-doped nanotubes in the polymer matrix. Due to the doping effect of SOCl2 the electrical conductivity of the composites is improved by a factor of 5. The light transmission of the composite films depends on the film thickness and on the nanotube concentration. The optical transmittance of visible light at 500 nm was found to be 92% for 0.1 wt% SWNT loading and 46% for 0.5 wt% SWNT loading. The thickness of the specimens was approximately 20 µm. Conductivity measurement of the thin films performed with the four lead method revealed values 3.5 × 10,3 S/cm and 4.7 × 10,1 S/cm, respectively. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanostructured polyolefins/clay composites: role of the molecular interaction at the interfacePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2008Elisa Passaglia Abstract The extent of interphase interactions between polymer phase and inorganic particles is the driving force addressing the preparation/properties design in the field of the corresponding micro- and nanocomposites. In the case of preparation of nanocomposites based on polyolefins (POs) and inorganic compounds as potentially nanodispersed phase, the use of a PO with proper functional groups is necessary for the interface adhesion and stabilization of the nanostructured morphology. According to this approach, ethylene/propylene copolymers with a different propylene content were used for the preparation of nanocomposites through melt mixing with organophilic montmorillonites (OMMT). By taking into account the important role of functionalities grafted onto POs, two different synthetic approaches were compared here: (1) the dispersion of the inorganic filler was obtained by using previously functionalized POs bearing carboxylate groups as matrices; (2) the nanocomposites were prepared by performing contemporaneously the functionalization of POs (by using maleic anhydride (MAH) and/or diethyl maleate (DEM)) and the dispersion of the filler in a one-step process. The morphology of the nanocomposites as well as the variation of solubility and glass transition temperature (Tg) of the PO matrix were evaluated and tentatively discussed with reference to functionalization degrees, structure of PO, and preparation procedure. Copyright © 2008 John Wiley & Sons, Ltd. [source] Matrix vapor deposition/recrystallization and dedicated spray preparation for high-resolution scanning microprobe matrix-assisted laser desorption/ionization imaging mass spectrometry (SMALDI-MS) of tissue and single cellsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 3 2010Werner Bouschen Matrix preparation techniques such as air spraying or vapor deposition were investigated with respect to lateral migration, integration of analyte into matrix crystals and achievable lateral resolution for the purpose of high-resolution biological imaging. The accessible mass range was found to be beyond 5000 u with sufficient analytical sensitivity. Gas-assisted spraying methods (using oxygen-free gases) provide a good compromise between crystal integration of analyte and analyte migration within the sample. Controlling preparational parameters with this method, however, is difficult. Separation of the preparation procedure into two steps, instead, leads to an improved control of migration and incorporation. The first step is a dry vapor deposition of matrix onto the investigated sample. In a second step, incorporation of analyte into the matrix crystal is enhanced by a controlled recrystallization of matrix in a saturated water atmosphere. With this latter method an effective analytical resolution of 2,µm in the x and y direction was achieved for scanning microprobe matrix-assisted laser desorption/ionization imaging mass spectrometry (SMALDI-MS). Cultured A-498 cells of human renal carcinoma were successfully investigated by high-resolution MALDI imaging using the new preparation techniques. Copyright © 2010 John Wiley & Sons, Ltd. [source] High-throughput determination of carbocysteine in human plasma by liquid chromatography/tandem mass spectrometry: application to a bioequivalence study of two formulations in healthy volunteersRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 7 2006Hui-chang Bi A rapid and sensitive liquid chromatography/tandem mass spectrometry (LC/MS/MS) method to determine carbocysteine in human plasma was developed and fully validated. After methanol-induced protein precipitation of the plasma samples, carbocysteine was subjected to LC/MS/MS analysis using electrospray ionization (ESI). The MS system was operated in the selected ion monitoring (SRM) mode. Chromatographic separation was performed on a Hypurity C18 column (i.d. 2.1,mm,×,50,mm, particle size 5,µm). The method had a chromatographic running time of 2.0,min and linear calibration curves over the concentration ranges of 0.1,20,µg/mL for carbocysteine. The lower limit of quantification (LLOQ) of the method was 0.1,µg/mL for carbocysteine. The intra- and inter-day precision was less than 7% for all quality control samples at concentrations of 0.5, 2.0, and 10.0,µg/mL. These results indicate that the method was efficient with a simple preparation procedure and a very short running time (2.0,min) for carbocysteine compared with methods reported in the literature and had high selectivity, acceptable accuracy, precision and sensitivity. The validated LC/MS/MS method has been successfully used to a bioequivalence study of two tablet formulations of carbocysteine in healthy volunteers. Copyright © 2006 John Wiley & Sons, Ltd. [source] Bioanalysis of pentoxifylline and related metabolites in plasma samples through LC-MS/MSBIOMEDICAL CHROMATOGRAPHY, Issue 6 2010Daniela Iuliana Sora Abstract Analytical aspects related to the assay of pentoxifylline (PTX), lisofylline (M1) and carboxypropyl dimethylxanthine (M5) metabolites are discussed through comparison of two alternative analytical methods based on liquid chromatography separation and atmospheric pressure electrospray ionization tandem mass spectrometry detection. One method is based on a ,pure' reversed-phase liquid chromatography mechanism, while the second one uses the additional polar interactions with embedded amide spacers linking octadecyl moieties to the silicagel surface (C-18 Aqua stationary phase). In both cases, elution is isocratic. Both methods are equally selective and allows separation of unknowns (four species associated to PTX, two species associated to M1) detected through specific mass transitions of the parent compounds and owning respective structural confirmation. Plasma concentration,time patterns of these compounds follow typical metabolic profiles. It has been advanced that in-vivo formation of conjugates of PTX and M1 is possible, such compounds being cleaved back to the parent ones within the ion source. The first method was associated with a sample preparation procedure based on plasma protein precipitation by strong organic acid addition. The second method used protein precipitation by addition of a water miscible organic solvent. Both analytical methods were fully validated and used to assess bioequivalence between a prolonged release generic formulation and the reference product, under multidose and single dose approaches. Copyright © 2009 John Wiley & Sons, Ltd. [source] Measurement of fexofenadine concentration in micro-sample human plasma by a rapid and sensitive LC-MS/MS employing protein precipitation: application to a clinical pharmacokinetic studyBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Daqing Guo Abstract A simple, rapid and sensitive liquid chromatography/positive ion electro-spray tandem mass spectrometry method (LC-MS/MS) was developed and validated for the quantification of fexofenadine with 100,,L human plasma employing glipizide as internal standard (IS). Protein precipitation was used in the sample preparation procedure. Chromatographic separation was achieved on a reversed-phase C18 column (5,,m, 100 × 2.1,mm) with methanol,:,buffer (containing 10,mmol/L ammonium acetate and 0.1% formic acid; 70,:,30, v/v) as mobile phase. The total chromatographic runtime was approximately 3.0,min with retention time for fexofenadine and IS at approximately 1.9 and 2.1,min, respectively. Detection of fexofenadine and IS was achieved by LC-MS/MS in positive ion mode using 502.1 , 466.2 and 446.0 , 321.1 transitions, respectively. The method was proved to be accurate and precise at linearity range of 1,600,ng/mL with a correlation coefficient (r) of ,0.9976. The validated method was applied to a pharmacokinetic study in human volunteers following oral administration of 60 or 120,mg fexofenadine formulations, successfully. Copyright © 2009 John Wiley & Sons, Ltd. [source] Generation of Equally Sized Particle Plaques Using Solid-Liquid SuspensionsBIOTECHNOLOGY PROGRESS, Issue 3 2006Tim Herrmann A device is presented for the generation of equally sized plaques of sensitive particles in a 96-well format. The resulting particle plaques can be used for the measurement of adsorption isotherms and uptake kinetics in protein chromatography or for immobilization reactions. The particle plaques are formed from suspensions with a vacuum device that is designed as a reusable sandwich module. The particles are retained by a mesh while the solvent is removed by the vacuum. As most particles used for protein chromatography are sensitive to mechanical stress and dehydration, the vacuum device is gentle enough to allow the use of these particles, thus eliminating the uncertainty of slurry preparation and pipetting. Apparatus characteristics and preparation procedures are described precisely. The physical intactness of the particles after the preparation procedure is proved by microscopic analysis. Data on the uniformity of the obtained resin plaques with respect to the reproducibility of their adsorption performance is given. Finally, adsorption isothermal and kinetic data of BSA on an ordinary HIC system obtained by high-throughput measurements are shown as an application example. [source] Role of the Preparation Procedure in the Formation of Spherical and Monodisperse Surfactant/Polyelectrolyte ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Yuxia Luan Dr. Abstract Complexes formed by a double-tail cationic surfactant, didodecyldimethyl ammonium bromide, and an anionic polyelectrolyte, an alternating copolymer of poly(styrene-alt-maleic acid) in its sodium salt form, were investigated with respect to variation in the charge ratio (x) between the polyelectrolyte negative charges and the surfactant positive charges. The morphology and microstructure of the complexes were studied by light microscopy and small-angle X-ray scattering for different preparation conditions. Independent of the sample preparation procedure and the charge ratio x, the X-ray results show that the microscopic structure of the complexes is a condensed lamellar phase. By contrast, the morphology of the complexes changes dramatically with the preparation procedure. The complexes formed by mixing a surfactant solution and a polyelectrolyte solution strongly depend on x and are always extremely heterogeneous in size and shape. Surprisingly, we show that, when the two solutions interdiffuse slowly, spherical complexes of micrometric and rather uniform size are systematically obtained, independently on the initial relative amount of surfactant and polyelectrolyte. The mechanism for the formation of these peculiar complexes is discussed. [source] Immediate functional loading of implants in single tooth replacement: a prospective clinical multicenter studyCLINICAL ORAL IMPLANTS RESEARCH, Issue 8 2008Mauro Donati Abstract Objectives: The aim of the present study was to evaluate the outcome of immediate functional loading of implants in single-tooth replacement using two different installation procedures. Material and Methods: One hundred and fifty-one subjects, who required single-tooth rehabilitation in the area of 15,25 and 35,45, were enrolled in eight private clinics in Italy. The implant sites were randomly allocated to one of the following treatment groups. In the control group, in which a standard preparation procedure for implant placement and submerged healing of the implant was used, abutment connection and loading of the implants were performed 3 months after installation. In the test group 1, a standard preparation procedure for the implant placement and immediate functional loading of implant was carried out. In the test 2 group, however, a modified implant installation procedure (osteotome technique) was used followed by immediate functional loading of the implant. Clinical and radiographic examinations were performed at 3 and 12 months of follow-up at all sites. Results: Three implants (5.5%) from the test 2 group (osteotome preparation) and one (2%) from the test 1 group (conventional drill preparation) failed to integrate and were removed one and three months after implant installation. The mean marginal bone loss assessed at 12 months was 0.31 mm (test 1), 0.25 mm (test 2) and 0.38 mm (control) (no statistically significant differences were found between the three treatment groups.) Conclusion: It is suggested that immediate functional loading of implants that are placed with a conventional installation technique and with sufficient primary stability may be considered as a valid treatment alternative in a single-tooth replacement. [source] Method development and validation for the analysis of didanosine using micellar electrokinetic capillary chromatographyELECTROPHORESIS, Issue 21 2005Swapna Mallampati Abstract A selective MEKC method was developed for the analysis of didanosine in bulk samples. Successful separation of didanosine from 13 of its potential impurities, derived from the various synthetic preparation procedures, was achieved. As CZE gave poor separation selectivity, MEKC was preferable. The use of EKC allowed achievement of the separation in a significantly shorter time than conventional HPLC. An anionic long-chain surfactant, lithium dodecyl sulfate (LiDS), was used as the pseudostationary phase and sodium tetraborate buffer as the aqueous phase. In order to obtain the optimal conditions and to test the method robustness, a central composite response surface modeling experiment was performed. The optimized electrophoretic conditions include the use of an uncoated fused-silica capillary with a total length of 40,cm and an ID of 50,,m, a BGE containing 40,mM sodium tetraborate and 110,mM LiDS at pH,8.0, an applied voltage of 18.0,kV, and the capillary temperature maintained at 15°C. The method was found to be robust. The parameters for validation such as linearity, precision, and sensitivity are also reported. Three commercial bulk samples were analyzed with this system. [source] Formation and decay of the ABTS derived radical cation: A comparison of different preparation proceduresINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2002Carola Henriquez Bleaching of a preformed solution of the blue-green radical cation 2,2,-azinobis (3-ethylbenzothizoline-6-sulfonic acid) (ABTS+·) has been extensively used to evaluate the antioxidant capacity of complex mixtures and individual compounds. The reaction of the preformed radical with free-radical scavengers can be easily monitored by following the decay of the sample absorbance at 734 nm. The ABTS radical cation can be prepared employing different oxidants. Results obtained using MnO2 as oxidant show that the presence of manganese ions increases the rate of [ABTS]+· autobleaching in a concentration-dependent manner. The radicals can also be obtained by oxidizing ABTS with 2,2, -azobis(2-amidinopropane)hydrochloride (AAPH) or peroxodisulfate (PDS). The oxidation by AAPH takes place with a large activation energy and a low reaction order in ABTS. The data support a mechanism in which the homolysis of AAPH is the rate-limiting step, followed by the reaction of ABTS with the peroxyl radicals produced after the azocompound thermolysis. On the other hand, the low activation energy measured employing PDS, as well as the kinetic law, are compatible with the occurrence of a bimolecular reaction between the oxidant and ABTS. Regarding the use of ABTS-based methodologies for the evaluation of free radical scavengers, radical cations obtained employing AAPH as oxidant can be used only at low temperatures, conditions where further decomposition of the remaining AAPH is minimized. The best results are obtained with ABTS derived radicals generated in the reaction of PDS with an ABTS/PDS concentration ratio equal (or higher) to two. However, even with radicals prepared by this procedure, stoichiometric coefficients considerably larger than two are obtained for the consumption of the radical cation employing tryptophane or p -terbutylphenol as reductants. This casts doubts on the use of ABTS-based procedures for the estimation of antioxidant capacities. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 659,665, 2002 [source] Characterization of natural wax esters by MALDI-TOF mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2009Vladimír Vrkoslav Abstract The applicability of matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) to the analysis of wax esters (WEs) was investigated. A series of metal salts of 2,5-dihydroxybenzoic acid (DHB) was synthesized and tested as possible matrices. Alkali metal (Li, Na, K, Rb, Cs) and transition metal (Cu, Ag) salts were studied. The matrix properties were evaluated, including solubility in organic solvents, threshold laser power that should be applied for successful desorption/ionization of WEs, the nature of the matrix ions and the mass range occupied by them, and the complexity of the isotope clusters for individual metals. Lithium salt of dihydroxybenzoic acid (LiDHB) performed the best and matrices with purified lithium isotopes (6LiDHB or 7LiDHB) were recommended for WEs. Three sample preparation procedures were compared: (1) mixing the sample and matrix in a glass vial and deposition of the mixture on a MALDI plate (Mix), (2) deposition of sample followed by deposition of matrix (Sa/Ma), and (3) deposition of matrix followed by deposition of sample (Ma/Sa). Morphology of the samples was studied by scanning electron microscopy. The best sample preparation technique was Ma/Sa with the optimum sample to matrix molar ratio 1 : 100. Detection limit was in the low picomolar range. The relative response of WEs decreased with their molecular weight, and minor differences between signals of saturated and monounsaturated WEs were observed. MALDI spectra of WEs showed molecular adducts with lithium [M + Li]+. Fragments observed in postsource decay (PSD) spectra were related to the acidic part of WEs [RCOOH + Li]+ and they were used for structure assignment. MALDI with LiDHB was used for several samples of natural origin, including insect and plant WEs. A good agreement with GC/MS data was achieved. Moreover, MALDI allowed higher WEs to be analyzed, up to 64 carbon atoms in Ginkgo biloba leaves extract. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||