Timothy J. Ward

Improved Cyclodextrin Chiral Phases: A Comparison and Review

Abstract Cyclodextrin chiral phases have been shown to be widely applicable for the separation of enantiomers, diastereomers, structural isomers and routine compounds. Two innovations have recently occured in this field. First, the efficiency and selectivity of the β-cyclodextrin column has been improved. Second, compatable TLC plates which produce separations analogous to the columns have been developed. These results are discussed subsequent to a brief review of published work. In addition, the mechanism of separation on cyclodextrin bonded media, solvent effects, temperature effects and structural effects on chiral separations are considered.

Facile Separation of Enantiomers, Geometrical Isomers, and Routine Compounds on Stable Cyclodextrin LC Bonded Phases

The effectiveness of employing stationary phases composed of chemically bonded cyclodextrin molecules in the high performance liquid chromatographic separation of a variety of different types of compounds is summarized. Over one hundred compounds, including optical, geometrical, and structural isomers, diastereomers, and epimers were successfully separated from each other via use of beta- or gamma-cyclodextrin bonded phases and aqueous methanolic mobile phases. The mechanism of separation is based upon inclusion complex formation between the compounds being separated and the cyclodextrin molecules bonded to the stationary phase. The effects of temperature, mobile phase composition and flow rate upon the chromatographic selectivity and resolution are described. The results indicate that the cyclodextrin columns may be more versatile, flexible, and effective compared to the conventional normal or reversed phase columns.

Effect of crown-ether surfactants on flame atomic absorption and flame emission signals of some monovalent cations

Abstract Two surface-active and one surface-inactive 18-crown-6 derivatives were synthesized and evaluated for their abilities to enhance flame atomic absorption and flame emission signals of monovalent cations. Enhancement of potassium signals were noted for the surface-active compounds but not for the surface-inactive compound. The critical micelle concentration was determined and compared to the degree of enhancement. Surfactant-induced signal enhancements are not due to the slight or moderate decrease in the size of the aerosol first produced in the nebulizing chamber. Additional mechanistic considerations are discussed.