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Liquid Composition (liquid + composition)
Selected AbstractsCE-MS method development for peptides analysis, especially hepcidin, an iron metabolism markerELECTROPHORESIS, Issue 15 2009Gaëlle B. Martin Abstract A method for the resolution of a peptides mixture including hepcidin-25, an iron metabolism marker, was developed by CE-ESI-MS. Several strategies were tested to optimize peptide separation, such as the addition of cyclodextrins or organic solvents in the BGE or the use of coated capillaries. Best results in terms of resolution, symmetry and efficiency were obtained with a BGE made of 500,mM ammonium acetate pH 4.5/ACN 70:30,v/v. Using the methodology of experimental design, BGE concentration, sheath liquid composition and MS-coupling parameters were then optimized in order to obtain the best signal intensity for hepcidin. Finally, a 225,mM BGE and a sheath liquid composed of isopropanol/water 80:20,v/v containing 0.5%,v/v formic acid were selected as it constitutes the best compromise for selectivity, peak shape and sensitivity. [source] Ammonium perfluorooctanoate as a volatile surfactant for the analysis of N -methylcarbamates by MEKC-ESI-MSELECTROPHORESIS, Issue 22 2006Geert Van Biesen Abstract Ammonium perfluorooctanoate (APFOA) was investigated as an MS-friendly surfactant for the analysis of a mixture of ten N -methylcarbamates with MEKC-ESI-MS. Because of the relatively low boiling point of perfluorooctanoic acid (,190°C), APFOA can be introduced into a mass spectrometer without the adverse effects of less volatile surfactants such as SDS. With a BGE consisting of 50,mM APFOA/isopropanol (IPA) 98:2 and with 30,kV applied, a very fast separation (,6,min) was possible with only one pair of analytes comigrating. Using an experimental design with four factors (voltage, nebulizer pressure, concentration of APFOA, and concentration of IPA) we were able to resolve all analytes in just over 11,min. Sheath liquid composition and flow rate, drying gas temperature and flow rate, and fragmentor voltage were then optimized for maximum signal intensity and S/N. It was found that the faster method gave better S/N because of narrower peak widths, and detection limits in SIM mode were between 0.01 (aldicarb) and 0.08,mg/L (methomyl). Calibration curves were prepared with standards of 0.50, 1.00, and 2.00,mg/L for the analysis of samples obtained after SPE of tap water spiked with the ten N -methylcarbamates at a level of 10,µg/L. All analytes showed very good recoveries (>86%), except for the most polar analyte aldicarb sulfone (recovery of 73%), testifying for the potential use of APFOA for this kind of analyses. [source] Crystallization of Highly Supercooled Silicate MeltsADVANCED ENGINEERING MATERIALS, Issue 12 2006M. Roskosz Crystallization of liquids in the system CaO-MgO-Al2O3 -SiO2 at one atmosphere has been studied at temperatures between the glass transition (Tg) and the solidus. To determine the textures, compositions and unit-cell parameters of the crystalline phases, the authors have characterized the experimental charges over a wide range of length scales by scanning and transmission electron microscopy, electron microprobe analyses, X-ray diffraction, and Raman spectroscopy. With increasing temperature, crystals tend to reach the equilibrium composition, but the relative importance of thermodynamic and kinetic factors is a single function of T - Tg, regardless of liquid composition. This feature is of considerable practical interest as it provides the possibility, not only to predict, but also to control the composition of the crystallizing phases. [source] Persistence effects in flavour release from liquids in the mouthINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2003Kevin M. Wright Summary The flavour of drinks, creams and liquid-like food consumed without chewing is an important quality factor for consumers and manufacturers alike, so reliable predictive models of flavour release from liquids in the mouth are highly desirable. In this paper we show how the breath-by-breath concentration of aroma in the headspace after swallowing an aliquot of liquid can be modelled using basic principles of interfacial mass transfer. This mechanistic model is used to fit the experimental data for dilute aqueous solutions of five aroma compounds consumed by trained panellists. It is shown that many aroma compounds give detectable concentrations in the exhaled breath several minutes after swallowing and after ten or more exhalations. The influence of liquid composition on this aroma persistence effect is discussed. [source] Characterization of differential ebulliometers for measuring activity coefficientsAICHE JOURNAL, Issue 1 2000J. David Raal Differential ebulliometry is a powerful and rapid procedure for obtaining infinitely dilute activity coefficients with potentially very good accuracy. Tedious degassing procedures are not necessary, as in a static method, and from only a few measurements full system phase behavior can be evaluated. The principal problem, precise evaluation of the equilibrium liquid composition from the known composition of a prepared solution charged to the apparatus, is well known but has so far defied adequate resolution. A system of exact self-consistent equations was developed for the characterization of an ebulliometer through a dimensionless ebulliometer constant. Evaluation of this constant from typical data and its subsequent use are illustrated for a system of known phase equilibrium behavior. Remarkably, the equations permit evaluation of the effective "static" holdups in various parts of the equipment without any volume measurements. Since one equation is redundant to the main purpose, it can be used for a consistency check of measured and calculated data. The equations also furnish a guide for the operation of ebulliometers. [source] Qualitative model of concrete acidification due to cathodic protection,MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 2 2008W. H. A. Peelen In this paper a mathematical description and numerical implementation for ion transport in concrete due to current passage is developed, in which the heterogeneous equilibrium between Ca2+, OH, and the solid Ca(OH)2 is incorporated. The description is based on the Nernst,Planck equation for ion transport, and reaction terms for the dissolution/precipitation of Ca(OH)2. This description was implemented in the finite element package Comsol Multiphysics. In this way Ca(OH)2 depletion in a zone at a CP anode adjacent to a bulk of concrete with Ca(OH)2 could be modelled in one calculation. Drawback of this model is that the kinetic parameters in the reaction terms are not known, and must be chosen high to ensure the dissolution of Ca(OH)2 to be in equilibrium. This proved numerically challenging and sometimes caused long calculation times. The growth rate of the zone without solid depends on the current density applied, concrete cover, the pore liquid composition and the diffusion constants of Ca2+ and OH,. This rate must be evaluated numerically. This qualitative model of anode acidification shows no participation of Na+; therefore transport properties of this ion do not affect the acidification rate of concrete. The same would hold for any other ion included in the model, which is not involved in electrochemical or chemical reactions. [source] The parameterization of solid metal-liquid metal partitioning of siderophile elementsMETEORITICS & PLANETARY SCIENCE, Issue 10 2003Nancy L. CHABOT We present a method for parameterizing solid metal-liquid metal partition coefficients for siderophile (metal-loving) elements as a function of the metallic liquid composition. Our parameterization method is based on an older theory of Jones and Malvin (1990), which stated that the metallic liquid is composed of metal and non-metal-bearing domains, and the domains are the dominant influence on the partitioning behavior. By revising the means by which the metal domains are calculated, our revised parameterization method is able to match experimental partitioning data from the Fe-Ni-S, Fe-Ni-P, Fe-Ni-S-P, and Fe-Ni-C systems. Mathematical expressions were derived for the solid metal-liquid metal partitioning of 13 siderophile elements. Elements that are chalcophile (S-loving), P-loving, or C-loving prefer the non-metal-bearing domains in the metallic liquid and, consequently, aren't fit by the parameterization method presented here. Possible applications for our parameterization method include modeling the crystallization of iron meteorites, planetary differentiation, and the solidification of Earth's inner core. [source] Utility of nonaqueous capillary electrophoresis for the determination of lidocaine and its metabolites in human plasma: a comparison of ultraviolet and mass spectrometric detectionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Magnus S. Anderson A nonaqueous capillary electrophoresis/electrospray mass spectrometry method for the separation of lidocaine (LID) and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), has been developed. The separation medium was: 70,mM ammonium formate and 2.0,M formic acid in acetonitrile/methanol (60:40 v/v). With a sheath liquid of methanol/water (80:20 v/v) containing 2% formic acid and positive ion detection, reproducible determinations (8,11% relative standard deviation (RSD)) of lidocaine and its metabolites were performed in spiked human plasma. The limits of detection (LODs) were between 69.1 and 337,nM. The influences of sheath liquid composition, nebulizing gas pressure and drying gas temperature on the separation were examined. Copyright © 2004 John Wiley & Sons, Ltd. [source] Experimental study of feasibility in kinetically-controlled reactive distillationAICHE JOURNAL, Issue 2 2005Madhura Chiplunkar Abstract Bifurcation studies predict limited ranges of feasibility for products in certain reactive distillations. These are closely related to the bifurcations in the singular points of dynamic models for simple reactive distillation (isobaric open evaporation with liquid phase reaction). A new dynamic model is described with constant vapor rate together with an experimental study for the reactive distillation of acetic acid with isopropanol to produce isopropyl acetate, catalyzed by Amberlyst-15 ion-exchange resin. An experimental apparatus with real-time measurement of liquid compositions based on Fourier transform infrared (FTIR) spectroscopy is described, and used to follow the composition dynamics at several initial conditions and Damköhler numbers (Da). The experimental results match model predictions that show four regions of behavior. For Da , 1, these show a stable node at acetic acid and several other fixed points as saddles. However, near Da , 2, both isopropanol and acetic acid are stable nodes and a quaternary singular point appears. The presence of two stable nodes requires the presence of a distillation boundary and, therefore, a limited feasibility for the bottom product compositions from continuous reactive distillation. For the reaction rates studied, the model predictions are closely consistent with the experimental findings, and are robust to variations in the vapor rate. These experiments are among the first to analyze the dynamics and feasibility in a kinetically-controlled reactive distillation and are consistent with previous studies for the reaction equilibrium limit, indicating the formation of a reactive azeotrope. © 2005 American Institute of Chemical Engineers AIChE J, 51: 464,479, 2005 [source] | |||||||||||||