ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

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Capillary electrophoretic separation of basic drugs using surface-modified C8 capillaries and derivatized cyclodextrins as structural/chiral selectors (1995)

Stålberg, O. ; Brötell, H. ; Westerlund, D.

Springer

Chromatographia 40 (1995), S. 697-704

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ISSN: 1612-1112

Keywords: Capillary electrophoresis ; Surface modified capillaries ; Derivatized cyclodextrins ; Peak shape optimisation ; Enantiomer and rotamer resolution ; Remoxipride and local anaesthetic drugs

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary Dynamic coating of bonded C8 fused silica capillaries with cationic amphiphiles is shown to minimize adsorption of basic drug molecules but also to facilitate control/reversal of electroosmotic flow. Optimization of the peak shapes was achieved by addition of cationic amphiphiles with a suitable mobility and adsorption to the capillary surface. The surface modification described, combined with the addition of cyclodextrins as selectors into the background electrolyte, resulted in unique CE systems showing excellent resolution for structural analogues. The separation of rotamers and enantiomers is demonstrated. Applications to the antipsychotic compound remoxipride and its related substances and to the chiral separation of asthma- and local anaesthetic drug enantiomers are given.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02315140

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2

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Characterization of the precolumn bio trap 500 C18 for direct injection of plasma samples in a column-switching system (1998)

Yu, Z. ; Westerlund, D.

Springer

Chromatographia 47 (1998), S. 299-304

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ISSN: 1612-1112

Keywords: Column liquid chromatography ; Plasma samples ; Direct injection ; Restricted-access media ; Column-switching

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary A new restricted access media (RAM) type of precolumn, Bio Trap 500 C18, for direct injection of plasma samples in column-switching systems was evaluated with respect to the elution of plasma proteins in different mobile phases, the loading capacity of plasma samples, the chromatographic behavior during plasma injections and protein contamination of the packing and sealings. More than 95% of plasma proteins could be excluded from the precolumn within three minutes for all selected mobile phases. Quantitative analyte recoveries could be obtained by injecting plasma samples ranging from 5 to 500 μL with the analyte mass〉150 ng onto a BioTrap 500 C18 column (20×4 mm I.D.). One precolumn tolerated about 15 mL of plasma injection without out noticeable change in retention and pressure. Clogging of the precolumn was encountered (≥45 mL of plasma) due mainly to the adsorption of proteins on the packing. The performance of the analytical column (Kromasil C18) was also examined. The column efficiency decreased by 60% after processing 45 mL plasma in total.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02466535

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3

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High performance liquid chromatography of disaccharides on a porous graphitic carbon column applying post-column derivatization with benzamidine (1996)

Koimur, M. ; Lu, B. ; Westerlund, D.

Springer

Chromatographia 43 (1996), S. 254-260

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ISSN: 1612-1112

Keywords: Column liquid chromatography ; Carbohydrates ; Anomer separations ; Post-column derivatization

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary A sensitive post-column fluoresence method based on the reaction of reducing sugars with a fluorigenic reagent (benzamidine) under alkaline conditions and elevated temperature is described. Optimum reaction conditions suitable for the detection of fluorescent reaction products have been investigated. A porous graphitized carbon column (shandon Hypercarb) was employed as the chromatographic solid phase and elution was isocratic by an aqueous acetonitrile mixture. A special problem in sugar analysis is the tendendy of anomer formation giving doublet peaks. This tendency varies largely among the different sugars, and systematic studies on conditions that eliminate this problem were performed. Efficient and selective separations of a series of disaccharides were obtained using high temperatures and a low concentration of acetonitrile in the mobile phase. The detection limits (S/N=3) with an injection volume of 20 μL ranged from 10–60 picomoles. Linear calibration graphs were obtained in the 2–20 μM concentration range (r 2〉0.99). A relative standard deviation between 1–3% (n=6) demonstrated good precision of the developed system.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02270990

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4

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The effect of conductivity tuning in chiral separations by CE; Using hydroxypropyl-β-cyclodextrin in combination with tetraalkylammonium ions (1998)

Stålberg, O. ; Hedeland, M. ; Pettersson, C. ; [et al.]

Springer

Chromatographia 48 (1998), S. 415-421

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ISSN: 1612-1112

Keywords: Capillary electrophoresis ; Conductivity tuning ; Chiral separation ; Peak symmetry ; Resolution expression

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary Different approaches how to handle the electromigration dispersion process that occurs in separation and determination of enantiomers are presented. The use of cyclodextrins as chiral selectors in resolution enantiomers involves the possibility to tune the conductivity of the sample band in order to obtain symmetrical and efficient peaks. Determination of impurities that migrate in the rear part of an overloaded main peak can be accomplished if the conductivity of the background electrolyte (BGE) is adapted to the conductivity of the sample band. This strategy was shown in determination of the content of D-sotalol in a mixture of L and D-sotalol. The efficiency and the symmetry of the overloaded L-sotalol peak was substantially improved by substitution of tetrabutylammonium ions for tetrapentylammonium ions as co-ions in the BGE. In this system it was possible to determine 0.2% w/w of the chiral impurity D-sotalol. A resolution model is presented and used qualitatively in the study where the complexation between the tetraalkyllammonium ions and the cyclodextrins is taken into account.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02467713

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5

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Chiral separation of local anaesthetics with capillary electrophoresis (1996)

Sänger-van de Griend, C. E. ; Gröningsson, K. ; Westerlund, D.

Springer

Chromatographia 42 (1996), S. 263-268

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ISSN: 1612-1112

Keywords: Capillary electrophoresis ; Local anaesthetics ; Enantiomer separation ; Triethanolamine ; Dimethyl-β-cyclodextrin

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary A chiral capillary electrophoresis system for the highresolution separation of the enantiomers of the local anaesthetics mepivacaine, ropivacaine, bupivacaine and prilocaine is described. Triethanolamine was added to the background electrolyte to obtain a negative electroosmotic flow and hence higher resolutions. The interactions of the local anaesthetics and their chemical analogues with the chiral selector, dimethyl-β-cyclodextrin, were studied. From a model describing chiral capillary electrophoresis, the association equilibrium constants were determined by curve-fitting. The separation of mepivacaine, ropivacaine and bupivacaine was due to the different mobilities of the free analytes in solution, whereas the separation of a pair of enantiomers of a single analyte was due to differences between the association equilibrium constantsK 1 andK 2. Branching of the alkyl chain, which was situated close to the cavity in the inclusion complex, had strong effects on the chiral separation of the enantiomers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02290307

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6

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Influence of mobile phase conditions on the clean-up effect of restricted-access media precolumns for plasma samples injected in a column-switching system (1997)

Yu, Z. ; Westerlund, D.

Springer

Chromatographia 44 (1997), S. 589-594

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ISSN: 1612-1112

Keywords: Column liquid chromatography ; Column-switching systems ; Restricted-access media precolumns ; Mobile phase composition

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary Various mobile phases including phosphate buffer, pure water and five kinds of biological buffers (pH around 7) were systematically studied in terms of their ability to clean-up plasma matrix on precolumns of restrictedaccess media in a column-switching system. The necessary washing time, buffer pH, type and content of organic modifier were evaluated with respect to plasma elution profiles on restricted-access media precolumns. The influence of different mobile phases on the recovery of plasma matrix from alkyl-diol silica precolumns was studied by means of a scanning spectrophotometer. Our results show that phosphate buffer near physiological pH with small amounts of 2-propanol or acetonitrile was prefereble for direct injection of large plasma volumes (500 μL). More than 93% of the proteins in a plasma matrix can be recovered within 3 min from the alkyl-diol silica C18 column (25 mx 4 mm I.D.) as measured at 280 nm for all selected mobile phases except for tris (hydroxymethyl) aminomethane buffer, from which only about 88% was obtained.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02466660

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7

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Multivariate evaluation of the separation performance in micellar electrokinetic capillary chromatography of peptides: Optimization (1998)

Thorsteinsdóttir, M. ; Westerlund, D. ; Andersson, G. ; [et al.]

Springer

Chromatographia 47 (1998), S. 141-151

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ISSN: 1612-1112

Keywords: Micellar electrokinetic capillary chromatography ; Enkephalin related peptides ; Response surface modelling ; Central composite designs

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary A simultaneous optimization of resolution, efficiency and migration times of enkephalin-related peptides in micellar electrokinetic capillary chromatography (MEKC) was performed. Six experimental variables; the surfactant concentration, the percentage of organic modifier, the ionic strength of the buffer, the injected plug length, the applied temperature and the sample solution composition were studied via central composite design (CCD). Large differences in separation performance were observed at a commonly used level of organic modifier in the background electrolyte. Partial least squares regression of the responses revealed that the experimental domain was too large and complicated to be explained by the model. A new CCD model was obtained with improved prediction ability at narrower ranges of the experimental factors, especially of the organic modifier. A conflict between maximum resolution and efficiency within the shortest analysis time was observed. Therefore, constraints were set on maximal resolution and analysis time, while solving for maximum efficiency. Optimal operating conditions were found at 35 mM sodium dodecyl sulfate (SDS), 5% v/v of acetonitrile, 1.9 mm injected plug length, 35°C and sample solution with no added micelles, giving high efficiency and resolution at short analysis time. The value predicted by the model was found to agree very well to the observed values, at the optimal experimental conditions, even on a new capillary.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02466573

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8

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Improvements in drug purity determination by capillary electrophoresis using UV-absorption and LIF-detection with a UV-laser (1997)

Stålberg, O. ; Westerlund, D. ; Hultin, U-K. ; [et al.]

Springer

Chromatographia 44 (1997), S. 355-361

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ISSN: 1612-1112

Keywords: Capillary electrophoresis ; Drug purity ; Frequency doubled laser ; Laser induced fluorescence ; Reduced electromigration dispersion

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary In drug purity determinations by capillary electrophoresis using UV-detection generally a relative high concentration of the main compound has to be injected. Principles how to handle overloading effects are described. NXX-066 is a drug with a native fluorescence which made it possible to use of CE system equipped with a LIF-detection unit. Monitoring drug purity determination with LIF detection results in an improved limit of quantification of the impurities and/or opens a possibility to avoid an overloaded main peak. A frequency doubled (FRED) argon ion laser set at 244 nm was used as excitation source in drug purity determination with the LIF-detection unit and the chemicals used were therefore carefully chosen in order to minimize the background noise level, which easily is enhanced when fluorescence detection is performed in the UV-range. The separation of the fluorescent NXX-066 analogues proved to be a difficult task, but an adequate resolution was obtained when β- and γ-cyclodextrins was added as structural selectors and the separation window was expanded by the use of a repressed/reversed electroosmotic flow. A comparison of the separation capability for the UV-detection system and the laser induced fluorescence detection system was performed, showing that the overloading effects of the main peak can be removed using the CE-LIF system and thereby obtain a substantially improved resolution of the analogues. A comparison of LC-UV and CE-UV for drug purity determination of a crude product from, synthesis of NXX-066 is also included in this paper where a good correlation of the results were obtained.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02466310

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