Unusual chromatographic enantioseparation behavior of naproxen on an immobilized polysaccharide-based chiral stationary phase.
ABSTRACT Enantioseparation of naproxen was performed on an immobilized polysaccharide-based chiral stationary phase (CSP), Chiralpak IA, in the normal-phase mode. The effects of polar alcohol modifier in mobile phase and column temperature on retention, enantioseparation, and elution order were investigated. Two unusual phenomena were observed. One was solvent-induced reversal of elution order for the two enantiomers. Not only the type but also the content of polar alcohol modifier could induce the reversal. Another uncommon phenomenon was peak deformation under some chromatographic conditions.
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ABSTRACT: The adsorption isotherms of the naproxen enantiomers were measured on a Kromasil Whelk-O1 column, eluted with mixtures of supercritical carbon dioxide and methanol or ethanol. Five chromatographic methods were used: frontal analysis, frontal analysis by characteristic points, elution by characteristic points, retention time method and the inverse method. In all methods, the effects of the two modifiers were compared. The use of these methods suffers from limitations due to supercritical fluid chromatographic instruments. These problems and drawbacks are discussed. The accurate and precise determination of the isotherm parameters was not possible with the instrument currently used. In contrast, the different methods allow to show qualitatively that the adsorption of the naproxen enantiomers show heterogeneous mechanism on the adsorbent surface common in chiral chromatography. Finally, the experimental high concentration elution band profiles of naproxen are compared with those calculated from the isotherm parameters provided by the five different methods.Journal of Chromatography A 09/2013; · 4.61 Impact Factor
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ABSTRACT: Polysaccharide-based chiral stationary phases (CSPs) or chiral packing materials (CPMs) have been frequently employed for analyzing and separating various enantiomers by high-performance liquid chromatography (HPLC). The polysaccharide derivatives dissolved in a solvent are usually coated on silica gel to be used as CSPs. This means that some solvents, which can swell or dissolve the derivatives, cannot be used as the eluents in HPLC. In this review, various immobilization methods of the polysaccharide derivatives are described. The immobilization often reduces the chiral recognition ability compared to that of the corresponding coated-type CSPs. This problem can be overcome by the versatility of eluent selection for the immobilized CSPs. Enantioseparations of various racemates on the immobilized commercial columns using the non-standard eluents are briefly summarized.Journal of chromatography. A. 06/2014;
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ABSTRACT: Enantioseparations were achieved for eleven 3,5-disubstituted hydantoins in HPLC under the normal phase mode using Chiralpak IA. The effects of polar alcoholic modifier and column temperature on retention and enantioseparation were determined. Importantly, we found two kinds of enantiomer elution order (EEO) reversals, which include solvent-induced EEO reversal for compound 9 and temperature-induced EEO reversals for compound 3 and compound 6. The phenomena of these EEO reversals were described for the first time in present work, which is helpful to elucidate the chiral separation mechanism of these hydantoins.Journal of chromatography. A. 06/2014;