Influence of the nature of the hydrocarbon solvent on the separation of propranolol enantiomer derivatives on a Pirkle-type chiral stationary phase

Abstract

The separation of phenylurea and phenylthiourea derivatives of propranolol enantiomers on a Pirkle-type chiral stationary phase has been investigated using a number of different hydrocarbon solvents in the eluent. The derivatives are separated on a column containing 3,5-dinitrobenzoyl-α-phenylglycine, covalently bonded to 5 µm aminopropylsilica using an eluent consisting of ‘hydrocarbon’, propan-2-ol and acetonitrile. Straight-chain, cyclic and branched alkanes and straight-chain alkenes with carbon numbers ranging from 5 to 12 were investigated. For any given type of solvent, increasing the carbon number consistently led to a decrease in peak resolution, whilst having little significant effect on retention. For any given carbon number, systematic differences in resolution and retention were observed between the different solvent types. The effect of a solvent type was not necessarily the same on both resolution and retention. Studies using samples of the single enantiomers indicated that the loss of resolution did not simply result from a reduction in chromatographic efficiency with the higher carbon number solvents. The effect of solvent viscosity could be correlated with resolution and this could therefore represent a parameter which should be considered during optimization of the separation. Optimization of resolution by adjustment of the choice of hydrocarbon solvent has the advantage that it need not necessarily affect the retention time of the enantiomers.