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Column Length (column + length)
Selected AbstractsCharacterization of Taylor vortex flow in a short liquid columnAICHE JOURNAL, Issue 12 2009Rensheng Deng Abstract We present a study on Taylor vortex flow in the annulus between a rotating inner cylinder and a stationary outer cylinder, featured with a wide gap (radius ratio is 0.613) and a short column (aspect ratio is 5.17). A particle image velocimetry (PIV) system was used to determine the position, shape, and velocity distribution of the vortices, by which the flow was also confirmed to lie in the nonwavy Taylor vortex regime for all operating conditions explored in this study. Our results suggest that end boundary effects are important, in which the vortex number decreases with decreasing column length. For a system with an aspect ratio of 5.17, six vortices appear in the gap with their position, size, and shape varying at different Reynolds numbers. The fluid velocities show an asymmetric feature with respect to the vortex centers, while the maximum axial and radial velocities increase almost linearly with the increasing reduced Reynolds number (Re , Rec). In addition, computational fluid dynamics study was employed under the same conditions, and its results agree well with the PIV measurements. Overall, this study provides a quantitative understanding of the formation of Taylor vortices in a constrained space. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Chemisorption of carbon dioxide on sodium oxide promoted aluminaAICHE JOURNAL, Issue 11 2007K. B. Lee Abstract New equilibrium and column dynamic data for chemisorption of carbon dioxide from inert nitrogen at 250, 350, and 450°C were measured on a sample of sodium oxide promoted alumina, which was found to be a reversible chemisorbent for CO2. The equilibrium chemisorption isotherms were Langmuirian in the low pressure region (p <2.0 kPa) with a large gas,solid interaction parameter. The isotherms deviated from the Langmuirian behavior in the higher pressure region. A new analytical model which simultaneously accounted for Langmuirian chemisorption of CO2 on the adsorbent surface and additional reaction between the gaseous and sorbed CO2 molecules was used to describe the measured equilibrium data. The heats of CO2 chemisorption and the additional surface reaction were, respectively, 64.9 and 37.5 kJ/mol. The column breakthrough curves for CO2 sorption from inert N2 on the chemisorbent as well as the desorption of CO2 from the chemisorbent by N2 purge at 350°C could be described by the linear driving force (LDF) model in conjunction with the new sorption isotherm. The same LDF mass transfer coefficients can be used to describe both sorption and desorption processes. The CO2 mass transfer coefficients were (i) independent of feed gas CO2 concentration in the range of the data at a given temperature, and (ii) a weak function of temperature. The ratio of the mass transfer zone length to the column length was very small due to highly favorable CO2 sorption equilibrium. Several sequential cyclic CO2 sorption,desorption column dynamic tests were conducted to demonstrate the apparent stability of the material. © 2007 American Institute of Chemical Engineers AIChE J, 2007 [source] Mass-transfer effects during separation of proteins in SMB by size exclusionAICHE JOURNAL, Issue 5 2003Joukje Houwing The chromatographic fractionation of proteins by size-exclusion chromatography in a simulated moving bed (SMB) is studied. During experimental fractionation of a mixture of bovine serum albumin (BSA) and myoglobin on Sepharose Big Beads, mass-transfer effects are shown to limit the performance of the SMB. The internal profiles, as well as the extract and raffinate compositions, are described well by a steady-state equivalent true moving-bed (TMB) model that incorporates mass-transfer effects. The selection of the particle size in SMB is a trade-off between productivity and mass transfer. Based on the equivalent TMB model, the optimum particle size and configuration of the SMB can be selected, at which preset performance criteria (purity, recovery) are met at specified flow-rate ratios, total column length, and pressure drop. For the current feed and apparatus, an optimal particle size of approximately 145 ,m is calculated for achievement of purities and overall recoveries of 95%. [source] Investigation of factors influencing the performance of open-tubular stationary phases in capillary electrochromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9-10 2003Ruth Freitag Abstract Silica-based, open-tubular capillary columns bearing C8-moieties were produced by the sol gel approach. The influence of experimental conditions adjusted during the preparation of the stationary phase on the performance of the resulting capillary column were investigated in terms of the plate height, the resolution, and the capacity factors, taking the separation of three non-charged polyaromatic hydrocarbons (naphthalene, phenanthrene, pyrene) as example. Acetone served as EOF marker. The optimal synthesis protocol was then used to prepare columns for an analogous investigation of the chromatographic parameters, namely the mobile phase composition, the applied voltage and temperature, as well as the column length, thickness, and inner diameter on the performance of the capillary columns. [source] Plukenetia huayllabambana sp. nov. (Euphorbiaceae) from the upper Amazon of PeruNORDIC JOURNAL OF BOTANY, Issue 4 2009Rainer W. Bussmann A new species of Plukenetia from the Peruvian Department of Amazonas is described. Plukenetia huayllabambana R. W. Bussmann, C. Téllez & A. Glenn sp. nov. seems to be endemic to rocky patches in the cloud forest region of Mendoza. The species is similar to Plukenetia volubilis L., a species widely known from the Caribbean and Latin America, and Plukenetia stipellata L. J. Gillespie, which is only known from Central America. Both of these species occur only up to about 1200,m a.s.l., while Plukenetia huayllabambana has only been found above 1300,m a.s.l. The new species distinctly differs in its small number of stamens, stylar column length, and very large fruits and seeds. In Peru, Plukenetia spp. are widely known as ,Sacha Inchi' (forest Peanut), and Plukenetia huayllabambana could have a good potential to become an income source for the local communities. [source] Serially coupled microcolumn reversed phase liquid chromatography for shotgun proteomic analysisPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 7 2009Dingyin Tao Abstract Microcolumn RPLC (,RPLC) is one of the optimum separation modes for shotgun proteomic analysis. To identify as many proteins as possible by MS/MS, the improvement on separation efficiency and peak capacity of ,RPLC is indispensable. Although the increase in column length is one of the effective solutions, the preparation of a long microcolumn is rather difficult due to the high backpressure generated during the packing procedure. In our recent work, through connecting microcolumns of 5, 10, and 15,cm length via unions with minimal dead volume, long microcolumns with length up to 30,cm were obtained, with which 318 proteins were identified from proteins extracted from Escherichia coli by ,RPLC-ESI MS/MS, and similar distributions of Mw and pI were found with single and various coupled microcolumns. Furthermore, by using MS/MS with improved sensitivity, with such a serially coupled 30,cm long microcolumn, 1692 proteins were identified within 7,h from rat brain tissue, with false positive rate (FPR) <1%. All these results demonstrated that serially couple microcolumns might be of great promising to improve the separation capacity of ,RPLC in shotgun proteomic analysis. [source] Mixed-mode chromatography/isotope ratio mass spectrometry,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2010James S. O. McCullagh Liquid chromatography coupled to molecular mass spectrometry (LC/MS) has been a standard technique since the early 1970s but liquid chromatography coupled to high-precision isotope ratio mass spectrometry (LC/IRMS) has only been available commercially since 2004. This development has, for the first time, enabled natural abundance and low enrichment ,13C measurements to be applied to individual analytes in aqueous mixtures creating new opportunities for IRMS applications, particularly for the isotopic study of biological molecules. A growing number of applications have been published in a range of areas including amino acid metabolism, carbohydrates studies, quantification of cellular and plasma metabolites, dietary tracer and nucleic acid studies. There is strong potential to extend these to new compounds and complex matrices but several challenges face the development of LC/IRMS methods. To achieve accurate isotopic measurements, HPLC separations must provide baseline-resolution between analyte peaks; however, the design of current liquid interfaces places severe restrictions on compatible flow rates and in particular mobile phase compositions. These create a significant challenge on which reports associated with LC/IRMS have not previously focused. Accordingly, this paper will address aspects of chromatography in the context of LC/IRMS, in particular focusing on mixed-mode separations and their benefits in light of these restrictions. It aims to provide an overview of mixed-mode stationary phases and of ways to improve high aqueous separations through manipulation of parameters such as column length, temperature and mobile phase pH. The results of several practical experiments are given using proteogenic amino acids and nucleosides both of which are of noted importance in the LC/IRMS literature. This communication aims to demonstrate that mixed-mode stationary phases provide a flexible approach given the constraints of LC/IRMS interface design and acts as a practical guide for the development of new chromatographic methods compatible with LC/IRMS applications. Copyright © 2010 John Wiley & Sons, Ltd. [source] Studies on azaspiracid biotoxins.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2002In this study, the performance of monolithic columns was evaluated for ultrafast liquid chromatography/mass spectrometry (LC/MS) analyses and for high-resolution separations of several azaspiracid biotoxin analogs. Because of their high permeability, monolithic columns offer a number of advantages over conventional packed columns; viz., very low backpressures and relatively flat van Deemter curves at high flow rates. That is, very high flow rates can be used for ultrafast analyses or, by using longer than normal columns, high-resolution separations are possible. In a series of experiments, we varied the mobile phase flow rates between 1 and 8,mL/min, and studied their impact on chromatographic parameters such as retention time, resolution, number of plates and pressure. The chromatographic run times could be reduced to ca. 30,s without a significant change in the separation efficiency. A signal intensity comparison revealed interesting differences between atmospheric-pressure chemical ionization (APCI) and electrospray ionization (ESI) in their flow-rate dependency. An explanation with respect to the behavior as of a mass-flow or a concentration-dependent device is given in the paper. Additionally, the column length was varied between 10 and 70,cm. As a result, the number of theoretical plates increased substantially. In the example shown in the report, an increase from 13,000 plates for a 10-cm column to 80,000 for a 70-cm column is demonstrated. In addition, the potential of the monolithic columns for high-resolution LC/MS separations is shown for a complex biotoxin mixture, which was separated on a 40-cm-long column. Copyright © 2002 John Wiley & Sons, Ltd. [source] HPLC of basic drugs using non-aqueous ionic eluents: evaluation of a 3,,m strong cation-exchange materialBIOMEDICAL CHROMATOGRAPHY, Issue 3 2010Phillip E. Morgan Abstract HPLC columns packed with 3,,m particle size HPLC Technology Techsphere SCX (propylsulfonic acid-modified) silica offer considerable advantages over 5,,m SCX packings in the analysis of basic drugs using 100% methanol eluents containing an ionic modifier such as ammonium perchlorate. The basic drugs studied included clozapine and norclozapine, olanzapine, quinine and quinidine, and amitriptyline, nortriptyline, imipramine and desipramine. The 3,,m column was not only more efficient for a given column length compared with 5,,m materials, but also elution times were less, a phenomenon observed in reversed-phase systems. The high efficiencies and excellent peak shapes obtained with the 3,,m SCX-modified packing together with the relatively low back-pressures attained show that such materials deserve serious consideration by laboratories involved in the analysis of basic drugs. Manufacturers should offer such packings as a matter of routine. Alternative ionic modifiers such as ammonium acetate are available for use with mass spectrometric detection if required. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||