Selection of the Mobile Phase for Enantiomeric Resolution via Chiral Stationary Phase Columns

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Abstract
The optimization of enantiomeric resolution by mobile phase variation was studied with the chiral stationary phase derived from R-N-(3,5-dinitrobenzoyl) phenylglycine covalently coupled to 5 μm spherical 3-aminopropyl silica. Chromatography was routinely performed with mobile phase compositions having polarities as high as 2.5 without column deterioration. The relative strength of a solvent as a hydrogen acceptor was found to be an important basis for selection of the polar component in a binary mobile phase. The substitution of tert-butanol for 2-propanol or ethanol in an alcohol/hexane mixture, for example, afforded improved separation factors with several enantiomers. In addition, the need for a polar mobile phase such as 50/50 methylene chloride/hexane to minimize non-specific polar absorption of enantiomers has been demonstrated. Enhancement of specific chiral interactions and suppression of interfering reactions have been obtained with a number of clinically relevant derivatives as model compounds.