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  • 1
    ISSN: 1432-1238
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 67 (1998), S. 579-583 
    ISSN: 1432-0630
    Keywords: PACS: 66.30; 68.35; 42.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 0.7 Al0.3As heterostructure layers grown by liquid phase epitaxy. GaS and As in a weight ratio of 2:1 were used as the diffusion sources. The source of GaS was carefully selected via X-ray diffraction analysis. Sulfur diffusion was carried out in a sealed quartz ampoule at a temperature of 820 °C and an arsenic pressure of 1 atmosphere. The carrier concentration profile from experimental results agrees well with the theoretical profile, which was calculated with the complementary error function solution assuming a segregation coefficient of m=1 at the hetero-junction interface. A smooth diffusion of sulfur was observed without any surface damage or hetero-interface defects. A double heterostructure laser was fabricated by employing sulfur diffusion. Cathode luminescence intensity analysis revealed that no damage was caused by sulfur diffusion at the active layer. Excellent characteristics such as a long life, a low threshold current, a fundamental transverse mode oscillation and a high modulation speed were obtained.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary electrophoresis ; Enantiomer separation ; Trimetoquinol ; Denopamine ; Timepidium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Two methods for the direct separation of the enantiomers of trimetoquinol hydrochloride, denopamine and timepidium bromide were investigated, namely capillary zone electrophoresis (CZE) using cyclodextrins (CDs) (CD-CZE) and high-performance liquid chromatography (HPLC) using chiral stationary phases (CSPs). By CZE, separation of the enantiomers of trimetoquinol was successfully achieved when using β-cyclodextrin (β-CD), heptakis(2,6-di-0-methyl)-β-cyclodextrin (DM-β-CD) and β-CD polymer, but direct HPLC separation of the enantiomers was not successful. The enantiomers of denopamine were successfully separated by both CZE, employing DM-β-CD under acidic conditions, and HPLC, with cyclodextrin immobilized CSPs (CD-CSPs). Timepidium bromide, which is a racemic drug, was successfully enantioseparated by both CD-CZE and HPLC with CD-CSPs. The CD-CZE mode was selected as the optical purity testing method for trimetoquinol and denopamine because of the superiority of capillary electrophoretic (CE) techniques. Method validation results obtained clearly show that the CE method would be useful as an quality control method for assessing the optical purity of the drugs.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Aminoglycosidic antibiotics ; DEAE-dextran ; Drugs ; Enantiomer separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Diethylaminoethyl (DEAE) dextran hydrochloride and three kinds of aminoglycosidic antibiotics; fradiomycin sulfate, kanamycin sulfate and streptomycin sulfate, were employed as chiral selectors in capillary electrophoresis, enantiomer separation. These selectors are cationic or basic because of amino functionality and therefore used for enantiomer separation of acidic compounds. To avoid adsorption of the basic or cationic selectors on the capillary inner surface, a coated capillary was employed. Among those tested, enantiomers of binaphthyl compounds and synthetic intermediates of diltiazem analogues were separated. Methanol addition was effective for the improvement of peak shape and resolution.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 42 (1996), S. 617-630 
    ISSN: 1612-1112
    Keywords: Capillary zone electrophoresis ; Chiral separation ; Chiral selectors ; Dextran and dextrin ; Drugs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polysaccharides such as dextrins, which are mixtures of linear α-(1,4)-linked D-glucose polymers, and dextrans, which are polymers of D-glucose units linked predominantly by α-(1,6) bonds, have been employed as chiral selectors in the capillary electrophoretic (CE) separation of enantiomers. Because these polymers are electrically neutral, the method is applicable to ionic compounds. Among the compounds tested the enantiomers of ibuprofen, naproxen, warfarin and the diltiazem synthetic intermediate 1,1′-binaphthyl-2,2′diyl hydrogen phosphate, which are anionic compounds, were successfully recognized by employing dextran or dextrin under neutral conditions. The enantiomers of basic or cationic drugs such as timepidium, primaquine, sulconazole, trimetoquinol, diltiazem and clentiazem were also successfully separated under acidic conditions. The effects of molecular mass and polysaccharide concentration on enantioselectivity were investigated. High concentrations of these polymers, especially dextrin, led to delayed migration times after repeated injections of the solutes into an uncoated capillary under neutral conditions. Consequently the capillary washing process was found to be very important to obtaining reproducible migration times in the system. A coated capillary was also investigated to overcome this problem. Finally, the method using electrically neutral polysaccharides was applied to the testing of the optical purity of the drug substances.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 48 (1998), S. 569-575 
    ISSN: 1612-1112
    Keywords: Capillary electrophoresis ; Oligonucleotides ; Dextran ; Polymer solution ; Purity testing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Capillary gel electrophoresis (CGE) has been recognized as an effective method for the analysis of oligonucleotides. CGE using polymer solutions is especially useful and effective compared with that using crosslinked gels, because of easy change of media. Replacement of media leads to the reproducible separation of analytes. We have investigated CGE analysis of oligonucleotides of less than 20 bases employing various kinds of polymers. Polyacrylamide, dextrin, dextran, pullakin, and poly(ethylene glycol) were used as sieving matrixes at concentrations of 0–30 %. Polydeoxythymidylic acids [p(dT)11–20] were used as a test sample. These small oligonucleotides were successfully resolved on the basis of their base number by CGE using some of these polymer solutions. In particular, dextran was found to be effective and baseline separation was observed when a 30 % dextran solution was employed. Some validations such as linearity and reproducibility were also established and this method was found to be an adequate quality control method for small oligonucleotides. Finally, CGE using a 30 % dextran solution was successfully applied to impurity profiling of some synthetic oligonucleotides.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral stationary phases ; Crown ether derivatives ; Amino compounds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The enantiomers of primary amino compounds have previously been resolved on a chiral stationary phase (CSP) CSP-18C6I, prepared by immobilizing (+)-18-crown-6 tetracarboxylic acid. In this study related chiral stationary phases were prepared in an effort to broaden the scope of CSP18C6I. CSP-18C6II, synthesized to investigate the effect of spacer length, resolved the enantiomers of 2-amino-1,2-diphenylethanol and 1-(1-naphthyl)ethylamine (1-NEA) (hydrophobic amino compounds) with the largerk values and smaller α values than on CSP-18C6I, probably because of the greater hydrophobicity of CSP-18C6II. Use of CSP-18C6III, synthesized by modification of carboxylic acid functionality of CSP-18C6II by introduction of another chiral moiety,S-1-NEA, resulted in larger α values for 2-amino-1-phenylethanol and 2-amino-1-phenylpropanol than on CSP-18C6II, but the enantiomers of 1-NEA were not resolved, because of steric hindrance between 1-NEA and the chiral moiety. The amide derivativeN-3,5-dinitrobenzoyl-1-(α-naphthyl)ethylamine (DNN) as π-acceptor (3,5-dinitrobenzoyl function) or π-donor (naphthylethylamide function), and no primary amino functionality, was resolved on CSP-18C6III. The mechanism of separation of the enantiomers of DNN was assumed to be the π−π interaction between the 3,5-dinitrobenzoyl function (π-acceptor) of DNN and theS-1-NEA moiety (π-donor) of CSP-18C6III.
    Type of Medium: Electronic Resource
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