Home About us Contact
|
Home About us Contact | ||
|
|
||
Phases Used (phase + used)
Selected AbstractsRecent progress in enantiomeric separation by capillary electrochromatographyELECTROPHORESIS, Issue 22-23 2002Jingwu Kang Abstract Recent progress in enantiomeric separations by capillary electrochromatography (CEC) is reviewed. The development of simple and robust CEC column technologies plays an important role for popularization of CEC. During the last several years, various approaches for the preparation of enantioselective columns have been reported. Currently, the monolithic column technology (continuous beds) represents the most advanced approach for the preparation of CEC columns. The development of new chiral stationary phase used for CEC is another important issue in this field. Fundamental investigations on electrochromatographic behaviors of various CSPs are necessary in order to understand the separation mechanism and thus improve the separation performance. Some chiral stationary phases performed better under nonaqueous CEC conditions than reversed-phase conditions. Coupling CEC with mass spectrometry (MS) provides a powerful tool for enantiomeric separation. Finally, some applications of enantiomeric separation by CEC are summarized. [source] Preservice elementary teachers' conceptions of moon phases before and after instructionJOURNAL OF RESEARCH IN SCIENCE TEACHING, Issue 7 2002Kathy Cabe Trundle This study focused on the conceptual understandings held by 78 preservice elementary teachers about moon phases, before and after instruction. Participants in the physics groups received instruction on moon phases in an inquiry-based physics course; participants in the methods group received no instruction on moon phases. The instructive effect of two different types of preinstruction interviews also was compared. The instruction on moon phases used in the study is from Physics by Inquiry by Lillian McDermott. In the study, the method of inquiry followed a qualitative design, involving classroom observations, document analysis, and structured interviews. Inductive data analysis identified patterns and themes in the participants' conceptual understanding. Results indicate that without the instruction, most preservice teachers were likely to hold alternative conceptions on the cause of moon phases. Participants who had the instruction were much more likely to hold a scientific understanding after instruction. The instruction appears to be more effective in promoting a scientific understanding of moon phases than instruction previously reported in the literature. It also appears that using a three-dimensional model or making two-dimensional drawings during the preinstruction interviews does not have instructive value. © 2002 Wiley Periodicals, Inc. J Res Sci Teach 39: 633,658, 2002 [source] Extension of the C18 stationary phase knowledge by using the carotenoid testJOURNAL OF SEPARATION SCIENCE, JSS, Issue 19 2010Eric LesellierArticle first published online: 16 AUG 2010 Abstract The carotenoid test for octadecylsiloxane-bonded stationary phases used in RPLC was developed some years ago. Additional experiments have now been performed with varied stationary phases. The effect of the bonding density and of the pore diameter on steric selectivity, polar surface activity and hydrophobicity was determined by using YMC series (J'Sphere and Pack ODSA). The test was also extended to estimate the phase evolution of several classical or hybrid silicas. The high loading phases were also studied, as well as the fused core silicas. The effect of the particle size reduction on the three previous phase properties was investigated in the goal to determine in which way this parameter could also modify the chemical properties of the phases. [source] Survey of heat transfer mechanisms in a slurry bubble columnTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2001Hanning Li Abstract Heat transfer mechanisms in the bulk and distributor regions of a slurry bubble column are investigated based on the measurements of local heat transfer in a 0.28 m diameter Plexiglas column. The gas, liquid and solid phases used are oil-free compressed air, tap water and 35 ,m glass beads. The slurry concentration and superficial gas velocity are varied from 0 to 40 vol% and 0.05 to 0.30 m/s respectively. Measurements have been made with a fast response heat flux probe which provided local instantaneous heat transfer coefficients. The time-averaged heat transfer coefficients in the bulk region were on average about 50% higher than the distributor region of the column. The wall region heat transfer coefficients are well predicted by the correlation of Deckwer et al. (1980). Heat transfer mechanism in column centre can be adequately described by the consecutive film and surface renewal model. Les mécanismes de transfert de chaleur dans le coeur et dans la région du distributeur d'une colonne à bulles à suspensions sont étudiés en mesurant le transfert de chaleur local dans une colonne en plexiglass de 0.28 m. Les phases gazeuse, liquide et solide utilisées sont de l'air cornprimé déhuilé, de l'eau du robinet et des billes de verre de 35 ,m. On a fait varier la concentration des suspensions et la vitesse de gaz superficielle de 0 à 40% en volume et de 0.05 à 0.30 m/s, respectivement. Les mesures ont été faites à l'aide d'une sonde de flux de chaleur à réponse rapide qui fournit les coefficients de transfert de chaleur instantanés locaux. Les coefficients de transfert de chaleur moyennés dans le temps dans le coeur étaient, en rnoyenne, environ 50% supérieurs à ceux de la région du distributeur dans la colonne. Les coefficients de transfert de chaleur de la région de la paroi sont bien predits par la cordation de Deckwer et al. (1980). Le mécanisme de transfert de chaleur au centre de la colonne peut ,tre adéquatement décrit par le modéle de renouvellement de surface et de film consécutif. [source] Column selection and method development for the separation of nucleoside phosphotriester diastereoisomers, new potential anti-viral drugs.BIOMEDICAL CHROMATOGRAPHY, Issue 6 2005Application to cellular extract analysis Abstract Analytical HPLC methods using derivatized cellulose and amylose chiral stationary phases used in normal and reversed-phase modes were developed for the diastereoisomeric separation of mononucleotide prodrugs (pronucleotides) of 3,-azido-2,,3,-dideoxythymidine (AZT). The resolutions were performed with two silica-based celluloses using normal and reversed-phase methodologies: Tris-3,5-dimethylphenylcarbamate (Chiralcel OD-H and Chiracel OD-RH) and Tris-methylbenzoate (Chiralcel OJ and OJ-R). Two amyloses phases, Tris-3,5-dimethylphenylcarbamate (Chiralpak AD) and Tris-(S)-1-phenylethylcarbamate (Chiralpak AS), were used in normal-phase mode. Additionally, we developed separation using two stationary phases with immobilized cyclodextrins in reversed-phase and polar-organic modes. The mobile phase and the chiral stationary phase were varied to achieve the best resolution. Different types and concentration of aliphatic alcohols, acetonitrile or water in the mobile phase were also tested for the different separation modes. An optimal baseline separation (Rs > 1.5) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. The different columns gave complementary results in term of resolution. Limits of detection and quantification were 0.12,0.20 and 0.40,0.67 µm, respectively. This analytical method was applied in a preliminary study for the pronucleotide 2 quantification in cellular extract. Copyright © 2005 John Wiley & Sons, Ltd. [source] Chiral recognition mechanisms with macrocyclic glycopeptide selectors,CHIRALITY, Issue 1 2009Alain Berthod Abstract Macrocyclic glycopeptide selectors are naturally occurring antibiotics produced by microorganisms. They were found to be excellent chiral selectors for a wide range of enantiomers, including amino acids. Four selectors are commercialized as chiral stationary phases (CSP) for chromatography. They are ristocetin, teicoplanin, vancomycin, and the teicoplanin aglycone (TAG). The key docking interaction for amino acid recognition was established to be a charge,charge interaction between the anionic carboxylate group of the amino acid and a cationic amine group of the macrocyclic peptidic selector basket. The carbohydrate units are responsible for secondary interactions. However, they hinder somewhat the charge,charge docking interaction. The TAG selector is more effective for amino acid enantioseparations than the other CSPs. The "sugar" units are however useful allowing for chiral recognitions of other analytes, e.g., ,-blockers, not possible with the aglycone. Thermodynamic studies established that normal phase and reversed phase enantioseparations were enthalpy-driven. With polar waterless mobile phases used in the polar ionic mode, some separations were enthalpy-driven and others were entropy-driven. The linear solvation energy method was tentatively used to gain knowledge about the chiral recognition mechanism. It appeared to be a viable approach with neutral molecules but it failed with ionizable solutes. With molecular solutes and the teicoplanin CSP, the study showed a significant role of the surface charge-induced dipole interaction and steric effects. The remarkable complementary enantioselectivity effect observed with the four CSPs is discussed. Chirality, 2009. © 2008 Wiley-Liss, Inc. [source] | ||||||||||