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  • 1
    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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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    ISSN: 1612-1112
    Source: Springer Online Journal Archives 1860-2000
    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
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electrophoresis 16 (1995), S. 564-573 
    ISSN: 0173-0835
    Keywords: Capillary electrophoresis ; Micellar electrokinetic chromatography ; Mixed micelles ; Dynamic modification ; Reversed electroosmosis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The separations of enkephalin-related peptides and protein kinase A peptide substrates, with the common structural feature -Arg-Arg-X-Ser-Val-, were studied in micellar electrokinetic chromatography (MEKC) systems and compared with the capillary zone electrophoresis (CZE) mode. The influence of the magnitude and the direction of the electroosmotic flow on the selectivity was studied. Reversed electroosmosis was obtained by adding a hydrophobic amine, dimethyldodecylamine, to the background electrolyte; the amine forms cationic micelles with a low critical micelle concentration (0.3 mM). The neutral micellar agent, Brij 35, competes with the amine for adsorption sites on the capillary surface decreasing the reversed electroosmosis. In such a system, mixed cationic micelles are formed to which the peptides were not distributed at low pH, but an improved resolution was obtained due to the effects on electroosmosis. In systems containing the less hydrophobic amine dimethyloctylamine, in which probably no mixed micelles are formed, an improved separation of protein kinase A peptide substrates was obtained due to distribution to Brij 35 micelles. In separations of enkephalins, a high pH gave very low efficiencies due to surface-analyte interactions, and the best CZE separations were obtained at low pH. Changes in migration order were observed in the pH range 2-3, possibly due to differences in peptide pKa values or conformation changes of the peptides. The enkephalins were only to a small extent distributed to the Brij 35 micelles, but this improved the separation at pH 2 compared to the CZE mode.
    Additional Material: 10 Ill.
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  • 8
    ISSN: 0173-0835
    Keywords: Enantioseparation ; Inclusion complexation ; Capillary zone electrophoresis ; Cyclodextrin ; Anaesthetic drugs ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: The enantiomers of five racemic anaestethic drugs were resolved with cyclodextrins using capillary zone electrophoresis. Parameters which affected the chiral resolution, such as type and concentration of cyclodextrin, temperature, and addition of organic modifier were investigated. The results show that the enantiomeric discrimination of the solutes is influenced by the structural shape of the solute molecules, separation temperature, and type of cyclodextrin. It was found that α-cyclodextrin was the best enantioselector for resolution of prilocaine and ketamine, while the enantiomers of mepivacaine, ropivacaine, and bupivacaine were resolved with β-cyclodextrin and/or modified β-cyclodextrins, i.e., methyl- and 2-hydroxypropyl-β-cyclodextrin, as chiral selectors. The length of the alkyl chain on the amino group of the drug molecule had a strong effect on the enantioresolution of mepivacaine, ropivacaine, and bupivacaine. Baseline separation of racemic ketamine was achieved with α-and methyl-β-cyclodextrin at 15°C. Addition of 5 M urea to the running buffer containing β-cyclodextrin at high concentrations resulted in the enantioseparation of prilocaine, mepivacaine, and ketamine. Enantioresolution was improved upon the addition of 10% methanol to the buffer containing urea and β-cyclodextrin. Generally, the complex formed between the S-enantiomers and modified β-cyclodextrins was stronger than the corresponding R-forms. An exception was prilocaine where the R-form gave a more stable complex both with α- and β-cyclodextrin.
    Additional Material: 4 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Electrophoresis 17 (1996), S. 325-332 
    ISSN: 0173-0835
    Keywords: Capillary zone electrophoresis ; Indirect UV detection ; Highly alkaline buffer ; Sugars ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A rapid and sensitive method for the analysis of sugars was developed by capillary zone electrophoresis (CZE) with indirect UV detection. A mixture of nine mono- and oligosaccharides was separated in about 20 minutes on a fused silica capillary in a highly alkaline (pH 〉 12) background electrolyte (BGE). With tryptophan as the marker detected at 280 nm the femtomole level detection of sugars was possible. The system was optimized by studies on the buffer pH, the marker concentration, as well as the inner diameter of the capillary. The indirect detection of sugars was also performed with a cationic marker, N-benzylcinchonidium chloride (BCDC). However, the detection sensitivity was much lower in comparison to the tryptophan marker system.
    Additional Material: 8 Ill.
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  • 10
    ISSN: 0173-0835
    Keywords: Enantioseparation ; α1-Acid glycoprotein ; Capillary zone electrophoresis ; Disopyramide ; Partial filling technique ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: A method using α1-acid glycoprotein (AGP) as chiral selector for disopyramide by means of affinity electrokinetic chromatography has been developed. In order to avoid UV absorbance interferences, less than the effective length of the capillary was filled with the chiral selector. The electrophoretic conditions were chosen to give opposite migration directions for the chiral selector and the analyte; AGP migrated away from the detector. Enantiomers of disopyramide were separated on a methylcellulose-coated capillary with 20 cm length to the detector. The enantioresolution of the solute was affected by the concentration of the chiral selector, the plug length of the selector in the capillary, and the applied voltage. Resolution factors and migration times decreased with reduction of the plug length, while the efficiency of the separation system and peak performance were improved by decreasing the separation zone. A special feature of the technique is an enhanced selectivity due to increasing separation of the enantiomers when the fastest has migrated from the selector zone, while the second one still is retained. Equations relating selectivity and resolution with the difference in effective plug lengths between the two enantiomers are developed. Optimized conditions yielding complete resolution, requiring an 0.75 mM AGP plug of only 4.5 cm effective length, also gave high efficiencies (about 400 000 plates/m) for both enantiomer peaks.
    Additional Material: 7 Ill.
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