Chromatographic behavior of diastereoisomers

Selection of high-performance liquid chromatographic methods in pharmaceutical analysis. II. Optimization for selectivity in normal-phase systems

Optimization of selectivity in normal-phase chromatography was studied. Using the same optimization criteria (Rs,min, Dmin, Rsb and Rsa) as in Part I the possible combination of "solvent strength" optimization by variation of the percentage of polar modifier in the less polar mobile phase and "solvent type" optimization by measuring the solvent selectivity of chloroform, acetonitrile, tetrahydrofuran and dioxane was examined. From the results it can be concluded that by replacement of medium-polarity solvents (chloroform, acetonitrile, tetrahydrofuran and dioxane) in the mobile phase, the selectivity of the separation can be significantly improved as the elution order is a function of solvent type belonging to Class P. In the separation of a steroid mixture dioxane provides the best properties for improving band spacing.

Solvent selectivity in the resolution of some regioisomeric and diastereomeric prostaglandin intermediates on silica

The possibilities of predicting the selectivity in the resolution of regioisomeric and diastereomeric prostaglandin intermediates on silica gel was investigated. A satisfactory correlation between log alpha and the solvent localization parameters m and m0 was obtained, confirming the importance of solvent-solute localization in determining alpha values. The results will be useful in developing further the theory of the selectivity of resolution.