Search

Enantiomer separations were performed on three beta-cyclodextrin-based chiral stationary phases (CSP) containing the pernaphthylcarbamoylated beta-cyclodextrin (CSP 1), peracetylated beta-cyclodextrin (CSP 2) and permethylated beta-cyclodextrin (CSP 3) as chiral selectors by capillary liquid chromatography and pressure-assisted capillary electrochromatography in this study. Triethylammonium acetate/MeOH or phosphate buffer/MeOH was used as the mobile phase. The experimental factors affecting chiral separations have been examined for each CSP, including pH of the buffers, methanol content and applied voltage. Under optimal separation conditions, a number of racemic compounds were resolved into their enantiomers on three cyclodextrin-based CSP. A comparative study on the performance of three CSP revealed the presence of carbonyl functional groups as well as aromatic rings in the cyclodextrin derivatives, enhanced the interaction between the analytes and CSP, and thus improved enantioselectivity of the CSP.

A novel single-isomer positively charged beta-cyclodextrin (beta-CD), mono-6(A)-butylammonium-6(A)-deoxy-beta-cyclodextrin tosylate (BuAM-beta-CD), has been synthesized, characterized, and used for the enantioseparations of alpha-hydroxy acids, carboxylic acids, and ampholytic analytes by capillary electrophoresis in acidic aqueous background electrolytes. The effective mobilities of all studied analytes decreased with increasing concentration of CD. Satisfactory resolutions were obtained for alpha-hydroxy acids over a wide range of chiral selector concentration. The optimum CD concentration was lower than 5 mM for the carboxylic acids, while higher than 20 mM for alpha-hydroxy acids. Inclusion complexation in combination with ion pair interaction seemed to account for the chiral discrimination process. The hydrogen bonding may provide secondary contribution for the chiral resolution of alpha-hydroxy acids. In addition, BuAM-beta-CD was further proved to be an effective chiral selector for anionic analytes by the baseline enantioseparation of a six-acid mixture within 20 min.

Rapid and efficient enantioseparation of halogen aryl alcohols and beta-blockers propranolol and pindolol in packed bed CEC (p-CEC) using as-prepared submicron porous silica chiral stationary phases (CSPs) has been achieved. Monodispersed 0.66 and 0.81 microm chiral submicron porous silica spheres were prepared using tetramethoxysilane and hexadecyltrimethylammonium bromide, followed by a hydrothermal treatment method with ammonia-ethanol to expand the pore of silica spheres without changing their spherical morphology. A proper specific surface of ca. 230 m(2)/g and pore sizes average of 6-8 nm were obtained by this method. The submicron porous silica spheres were modified with mono-6-phenylcarbamoylated beta-CD via thiol-en radical addition. They were packed into 9 cm 50 microm id capillary columns with photopolymerized monolithic frits. These submicron CSPs showed greater column efficiency (about 476 000 plates/m for 4-iodophenyl-1-ethanol) and higher resolution than the corresponding 3 microm CSP.

A novel chiral stationary phase (CSP) was prepared by anchoring mono-6-azido-6-deoxyperphenylcarbamated beta-CD onto omega-alkynyl functionalized silica (5 microm) via organic soluble Cu(I)-catalyzed Click chemistry. The obtained CSP was thereafter packed into fused-silica capillary (100 microm id) with an effective length of 9 cm and tested in aqueous CEC to separate a series of racemic aryl alcohols. High separation factors with good resolution were achieved using the current novel CSP. Some pharmaceutical compounds could also be well resolved on this newly derived CSP. The analytical results demonstrate that Click-chemistry-based perphenylcarbamated CSP affords high stability in high electric field and depicts excellent enantioseparation in CEC. The effects of pH value, buffer concentration, applied voltage, concentration of organic modifier and analyte structure on the enantioseparation are also discussed.

Perphenylcarbamoylated beta-cyclodextrin bonded-silica particles (5 microm) were packed into 75-mum fused-silica capillaries, and used for the enantiomer separation of neutral and basic solutes by pressure-assisted capillary electrochromatography. Triethylammonium acetate and phosphate buffer were employed as the BGEs. A cathodic EOF was observed with these two BGEs. Seven chiral analytes were successfully resolved into their enantiomers under optimized conditions, and five of them could be baseline-separated within 12 min due to their high electrophoretic mobility. Better results were achieved with phosphate buffer as the BGE. The effects of organic content and pH on the enantioseparation were also investigated.