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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 57 (1985), S. 1835-1840 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Analytical chemistry 65 (1993), S. 3484-3488 
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 7 (1995), S. 23-27 
    ISSN: 0899-0042
    Keywords: felodipine ; retention model ; micellar mobile phases ; chiral resolution ; CHIRAL-AGP ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A retention model for the chiral separation of an uncharged solute, felodipine, on CHIRAL-AGP, using a micellar mobile phase is proposed. The model assumes the presence of two stereoselective sites and each enantiomer was found to interact with different sites. Addition of a chiral aliphatic alcohol, (+)-(S)-2-octanol, preferentially interacted with the binding site for (-)-(S)-felodipine. The monomeric form of the micellar agent (Tween® 20) competed with the enantiomers for the adsorption sites, and the formation of a 1:1 complex between the enantiomers and the micelles was assumed. The retention of the solutes was effectively controlled by adding small quantities (〈1.63 × 10-3 M) of the nonionic detergent Tween 20 to the mobile phase. Baseline separation was achieved by addition of 1.0 mM n-octylamine to the mobile phase; 8.14 × 10-4 M Tween 20 in phosphate buffer pH 7.0. The separation factor (α = 1.74) was unaffected by the detergent concentration in the presence of 1.0 mM n-octylamine. © 1995 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 4
    ISSN: 0899-0042
    Keywords: chiral resolution ; hydrophobic amines ; α1-acid glycoprotein ; Tween® 20 ; anionic additives ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The retentions and enantiomeric resolutions of remoxipride, propranolol, and trimipramine were studied using a CHIRAL-AGP column with micellar mobile phases and aliphatic, anionic additives. The retentions of the compounds, which in neat buffer solution were very high (k′ 〉 50), could be decreased to k′ 〈 10 by adding a mixture of Tween® 20 and heptanoic acid to the mobile phase. The presence of the aliphatic acid was essential in order to increase the enantiomeric selectivity. An efficiency enhancement was obtained by increasing the temperature. With a mobile phase composition optimized for the separation of remoxipride, the possibility of detecting levels of the enantiomeric impurity (R-remoxipride) down to 0.025% in the drug was demonstrated. © 1993 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Microcolumn Separations 2 (1990), S. 164-165 
    ISSN: 1040-7685
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' Zeitschrift für analytische Chemie 352 (1995), S. 705-711 
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A three-factor central composite face design (CCF) has been used for the optimization of the chiral resolution of the enantiomers of alprenolol, oxprenolol, trimipramine and propranolol on CHIRAL-AGP. The variables (factors) investigated were pH and concentrations of the micellar agent Tween® 20 and heptanoic acid. The responses evaluated were resolution (RS), capacity factor (k′) of the last eluted enantiomer and a chromatographic response function (CRF) defined as CRF = P5/log tret, where P is the peak-valley ratio according to Kaiser and tret is the retention time. The computed models, one for each substance and one for each response (in total 12 models), showed that the main factor for the regulation of RS as well as k′ and CRF in the experimental domain is the pH. The optimal pH for the substances could be found between pH 5.5 and 6.5. The optimum was evaluated by generating contour plots for the CRF models. The computed mathematical models were statistically evaluated and the predictive power of the models was tested by experimentation.
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  • 7
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0173-0835
    Keywords: Capillary zone electrophoresis ; Micellar electrokinetic chromatography ; Taurodeoxycholate ; Protein kinase A peptide substrates ; Structure - retention factor relationships ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The separation of protein kinase A peptide substrates with the general formula -X-Arg-Arg-Ala-Ser-Y-, where X and Y may be the same or different amino aicds, was studied by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). Taurodeoxycholate (TDC) was used as the micellar agent. CZE was effective in separating a peptide series differing in the number of amino acids, but not for a series with a difference in the terminating amino acid. For the latter series, MEKC generally gave a higher selectivity, but some of the peptide pairs were more easily separated by CZE, demonstrating the complementary character of the two techniques. The efficiency of the MEKC system was typically 〈 50% of that of CZE, but its higher selectivity generally outbalanced the lower efficiency regarding resolution. The distribution of the peptides to the micelles was studied by determination of retention factors. Electrostatic and hydrophobic forces were found to be determining factors in the distribution; the most highly charged basic peptides were most heavily distributed, and for peptides with the same charge those containing more hydrophobic amino acids were more strongly distributed. The contribution of some structural features to the distribution degree was also determined.
    Additional Material: 5 Ill.
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  • 9
    ISSN: 0173-0835
    Keywords: Detectability improvements ; Isotachophoretic preconcentration ; Frequency doubled argon ion laser ; Hydrodynamic backpressure programming ; Capillary zone electrophoresis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Due to the small path length and low injection volume the concentration limit of detection is comparatively poor in capillary electrophoresis (CZE) with UV detection. This limitation can be overcome by means of preconcentration methods and/or improved detection techniques. This paper describes a strategy where isotachophoresis (ITP) is used to preconcentrate a new cholinesterase inhibitor (NXX-066) prior to a capillary zone electrophoresis analysis in the same single capillary. A hydrodynamic backpressure is used to prevent the analyte from migrating out of the capillary. Laser-induced fluorescence (LIF) is used to further increase the detectability. The total gain in detectability with ITP-CZE-LIF compared to CZE-UV was at least 5500-fold, and it is possible to determine NXX-066 at the 1 nM level. The ITP-CZE method was further evaluated for two β-blockers; the mean coefficient of variation of the peak areas was 3.4% and the linearity of the calibration plots was satisfying.
    Additional Material: 5 Ill.
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  • 10
    ISSN: 0173-0835
    Keywords: Capillary zone electrophoresis ; Amino-coated capillaries ; Reversed electroosmosis ; Brij 35 ; Taurodeoxycholic acid micelles ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Enkephalin-related peptides were separated at low pH in a capillary with covalently bonded aminopropyl groups. The peptides are electrostatically repelled from the capillary surface and much higher efficiencies and faster separations were achieved compared to separations using uncoated capillaries. At low pH the amino groups are protonated, which results in reversed electroosmosis. The influence of voltage and ionic strength on the mobility and the separation efficiency was studied. The repeatability of migration times within one day was very good with relative standard deviations of 0.3-0.7%. Increasing the pH decreased the electroosmosis, eventually turning towards the cathode in the pH range 5-6; the separation performance, however, was lower at higher pH. Neutral and anionic micellar agents were added to the background electrolyte at different concentrations; the enkephalins had weak association with the neutral micellar agents but were distributed to the anionic taurodeoxycholic acid (TDC) micelles, giving rise to changes in separation selectivities. Very high efficiencies were obtained for peptides with a low distribution to the TDC micelles, while the efficiencies were impaired for those with a strong association with the micelles, which may indicate a slow mass transfer in the association process.
    Additional Material: 8 Ill.
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