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  • Enantiomers  (6)
  • Chiral separations  (3)
  • Column-coupling system  (1)
  • 1
    Electronic Resource
    Electronic Resource
    A further study on the chiral separation power of a soluble neutral β-cyclodextrin polymer (1995)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 18 (1995), S. 348-352 
    Details
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Enantiomers ; Cyclodextrin polymer ; Organic modifiers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Enantiomeric separation of some basic compounds, namely selegiline, amphetamine, and clenbuterol, was studied by capillary electrophoresis using an uncharged β-cyclodextrin polymer added to the background electrolyte at pH 2.5. Both complexation and resolution were influenced by the concentration of the chiral polymer confirming our previous results obtained in our earlier work for a wide number of pharmaceutical compounds. In this further study, we examined the influence of different organic additives to the background electrolyte on the enantioselectivity of the chiral selector, also using an extended number of analytes. In most cases, the use of an organic additive resulted in a decrease of resolution. However opposite to that, in some cases, e.g. ephedrine, the organic solvent proved to be essential to achieve enantiomeric resolution. Furthermore the influence of the capillary temperature on the resolution of the analytes was evaluated. Increase of temperature had a deleterious effect on the resolution of the enantiomers. For ephedrine, however, relatively high temperature (50 °C) proved to be advantageous, for the resolution of the optical isomers.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240180605
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  • 2
    Electronic Resource
    Electronic Resource
    Separation of tryptophan-derivative enantiomers with iron-free human serum transferrin by capillary zone electrophoresis (1995)
    Weinheim : Wiley-Blackwell
    Electrophoresis 16 (1995), S. 1510-1518 
    Details
    ISSN: 0173-0835
    Keywords: Chiral separation ; Enantiomers ; Human serum transferrin Stereoselective interactions ; Capillary zone electrophoresis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Enantiomers can be separated by using human serum transferrin as a chiral phase. With the help of the native protein we were able to separate enantiomers with high efficiency, using a low ionic strength 2-(N-morpholino)ethanesulfonic acid (MES) buffer, pH 6, in capillary zone electrophoresis. Tryptophan methyl, ethyl and butyl ester enantiomers - moving towards the cathode at pH 6 - were resolved by passing through an iron-free transferrin zone in coated capillaries. Since the isoelectric point of the iron-free transferrin is a little higher than 6, the protein zone is either not moving in the experiment or is slowly moving towards the anode. Under the simplest experimental conditions the highest resolution was obtained for the butyl ester enantiomers and the lowest for the methyl ester ones. By changing the experimental conditions, however, this order could be reversed. The results indicate that the lengths of the alkyl chains in the enantiomers have a significant effect on the resolution, i.e., on the interaction between the protein and the separands.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.11501601250
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  • 3
    Electronic Resource
    Electronic Resource
    Further study on the use of uncharged β-cyclodextrin polymer in capillary electrophoresis: Enantiomeric separation of some α-hydroxy acids (1995)
    Weinheim : Wiley-Blackwell
    Electrophoresis 16 (1995), S. 1505-1509 
    Details
    ISSN: 0173-0835
    Keywords: Enantiomers ; Capillary electrophoresis ; Cyclodextrin polymer ; α-Hydroxy acids ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Uncharged β-cyclodextrin polymer was used as chiral selector for the enantiomeric separation of some α-hydroxy acids by capillary electrophoresis. Complexation and enantiomeric resolution of mandelic acid, m-hydroxy and p-hydroxymandelic acid, 3,4-dihydroxymandelic acid, as well as 2- and 3-phenyllactic acid were studied, changing the concentration of the β-cyclodextrin polymer added to the background electrolyte at different pH in the range of 4.5-7. Furthermore, the effects of the concentration of the background electrolyte, column temperature, and applied voltage on chiral resolution were also examined. The best enantiomeric separations were obtained using a background electrolyte at pH 6 containing 100 mg/mL of β-cyclodextrin polymer.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.11501601249
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  • 4
    Electronic Resource
    Electronic Resource
    A practical procedure for the determination of association constants of the analyte-chiral selector equilibria by capilllary zone electrophoresis (1996)
    Weinheim : Wiley-Blackwell
    Electrophoresis 17 (1996), S. 1921-1924 
    Details
    ISSN: 0173-0835
    Keywords: Capillary zone electrophoresis ; Chiral separations ; Association constants ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A practical procedure is proposed for the determination of association constants and mobility of the associate of a solute with a chiral selector in chiral separations by capillary zone electrophoresis. The procedure is based on the measurement of the effective mobility of a solute at zero and two different nonzero concentrations of the chiral selector. Simple explicit formulas have been derived in order to calculate the required data. The essence of the procedure is that all mobility data are adjusted to the background electrolyte (BGE) without chiral selector, serving as the viscosity reference. A simple procedure is described for measuring the viscosity of the operational electrolytes directly with the commercial capillary electrophoresis instrumentation, and Walden's rule has been utilized for adjusting the experimental mobility data to constant reference viscosity. The use of the procedure is exemplified by a separation of D,L-tryptophan in BGE containing α-cyclodextrin as chiral selector.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150171219
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  • 5
    Electronic Resource
    Electronic Resource
    Use of a Hepta-tyr glycopeptide antibiotic as chiral selector in capillary electrophoresis (1998)
    Weinheim : Wiley-Blackwell
    Electrophoresis 19 (1998), S. 1742-1751 
    Details
    ISSN: 0173-0835
    Keywords: Antibiotics ; Chiral separations ; Enantiomers ; Drugs ; Herbicides ; Capillary electrophoresis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A new glycopeptide antibiotic, MDL 63,246 (Hepta-tyr), of the teicoplanin family, has been evaluated in capillary electrophoresis for the resolution of chiral compounds of pharmaceutical and environmental interest. Electrophoretic separations were carried out in a polyacrylamide-coated capillary using the partial filling-counter current mode with aqueous-organic buffers in the pH range 4-6. Experimental parameters affecting resolution, such as antibiotic concentration, buffer pH, organic modifier type and capillary temperature, were studied. The Hepta-tyr antibiotic exhibited a high enantiorecognition capability towards the studied compounds at very low concentrations (1-2 mg/mL). The optimum experimental conditions were achieved by using a buffer at pH 5 containing acetonitrile at 25°C.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150191036
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  • 6
    Electronic Resource
    Electronic Resource
    Stereoselective analysis of herbicides by capillary electrophoresis using sulfobutyl ether β-cyclodextrin as chiral selector (1997)
    Weinheim : Wiley-Blackwell
    Electrophoresis 18 (1997), S. 227-234 
    Details
    ISSN: 0173-0835
    Keywords: Herbicides ; Enantiomers ; Cyclodextrin ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Capillary zone electrophoresis has been used for the enantiomeric separation of several herbicides. Different β-cyclodextrin (CD) derivatives have been investigated for chiral separations and among them the negatively charged sulfobutyl ether β-cyclodextrin (SBE-β-CD) proved to be effective for the stereoselective resolutions of the investigated herbicides. The effect of CD concentration, buffer pH and organic modifier on effective mobilities, resolution and selectivity of the analytes have been studied. Addition of SBE-β-CD (5-50 mg/mL) to the buffer at pH 9 resulted in a general increase of migration times as well as resolution. A CD concentration as low as 5 mg/mL was effective to completely resolve napropamide and ethofumesate enantiomers. Buffer solutions containing 40 mg/mL of SBE-β-CD were chosen to study the effect of buffer pH (7, 8, and 9) on chiral separation of the herbicides. No great differences in resolution and effective mobilities have been found in the pH 7-9 range. The addition of different organic modifiers to the background electrolyte at pH 9, containing 20 mg/mL of SBE-β-CD, showed different effects. Methanol was the most effective in improving resolution but in some cases total loss in enantiomeric separation was observed. The qualitative analysis of an enantiomerically pure herbicide (flamprop isopropyl) commercial preparation is also shown.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150180209
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  • 7
    Electronic Resource
    Electronic Resource
    Use of cyclodextrins in capillary electrophoresis: Resolution of tramadol enantiomers (1998)
    Weinheim : Wiley-Blackwell
    Electrophoresis 19 (1998), S. 2883-2889 
    Details
    ISSN: 0173-0835
    Keywords: Tramadol ; Enantiomers ; Cyclodextrins ; Capillary zone electrophoresis ; Validation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Capillary zone electrophoresis was successfully applied to the enantiomeric resolution of racemic tramadol. Both uncoated and polyacrylamide-coated capillaries were tested for method optimization using either negatively charged or native cyclodextrins (CD) added to the background electrolyte (BGE). The resolution was strongly influenced by the CD type and concentration as well as by the pH and the concentration of the BGE. Among the CDs tested, carboxymethylated-β-cyclodextrin allowed the baseline separation of tramadol enantiomers. After the method was optimized, it was validated in a coated capillary for enantiomeric analysis of tramadol enantiomers in pharmaceutical formulation, including specificity and elution order, linearity, accuracy and precision, determination of limit of detection (LOD) and quantification (LOQ), enantiomeric purity linearity, freedom from interference, and stability of sample solutions. Precision at the target concentration was less than 2%, with an accuracy higher than 99%. Furthermore, the method was able to detect 0.3% and to quantify 1% of the minor enantiomer in the presence of the major one at the target value.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.1150191614
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  • 8
    Electronic Resource
    Electronic Resource
    Highly sensitive chiral analysis in on-line combined chiral and achiral media by capillary zone electrophoresis (1995)
    Weinheim : Wiley-Blackwell
    Electrophoresis 16 (1995), S. 968-973 
    Details
    ISSN: 0173-0835
    Keywords: Capillary zone electrophoresis ; Chiral separations ; Column-coupling system ; α-Hydroxycarboxylic acids ; Sensitivity of optical detection ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A new approach is described for highly sensitive chiral analyses by capillary zone electrophoresis, based on using an on-line combination of two capillaries filled with either chiral selective or achiral background electrolytes (BGE). Thus, the BGEs are selected in such a way that the first capillary provides optimum chiral selectivity and the second one optimum detection sensitivity. Direct chiral separations of enantiomers of mandelic, m-methoxymandelic, 3-phenyllactic and 3-indolelactic acids served as a model example for testing the approach proposed. The analyses were performed in a BGE containing acetate as a coion and L-OH-proline or aspartame as a chiral selector. For high sensitive analyses, an arrangement containing on-line combined chiral and achiral media were tested in one or two capillaries coupled via a bifurcation block. A detection limit as low as 10-18 moles was reached in the column-coupling system when the direct chiral separation was performed in the first capillary, filled with 20 mM acetate buffer, pH 4.4, containing 8 mM Cu (II) and 16 mM aspartame (L-aspartyl-L-phenylalanine methylester) and separated enantiomers were detected in the second capillary, filled with 20 mM acetate buffer, pH 3.1. The principle described is of general use in cases where the separation and detection of analytes in question require mutually different BGEs to reach the optimum selectivity and sensitivity, respectively.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/elps.11501601162
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