Enantiomeric separation of β-blockers by HPLC using ( R)-1-naphthylglycine and 3,5-dinitrobenzoic acid as chiral stationary phase

Direct liquid chromatographic separations of the enantiomers of metoprolol and bisoprolol have been developed, using ( R)-1-naphthylglycine and 3,5-dinitrobenzoic acid as chiral stationary phase (CSP). The separations were achieved in a normal phase system employing a mobile phase containing n-hexane, 1,2-dichloroethane and methanol. Column efficiency was strongly dependent on the composition of the mobile phase. The eluent contents of methanol and of 1,2-dichloroethane were optimized, and so was flow-rate and column temperature. Under the optimal conditions, linear responses for ( R)-metoprolol and ( S)-metoprolol are obtained in the range of 0.079–1.38 and 0.015–5.80 mg/ml, with detection limits of 0.008 and 0.002 mg/ml, respectively. As for bisoprolol, the linear ranges of ( R)-isomer and ( S)-isomer are 0.05–1.31 and 0.02–1.00 mg/ml with detection limits of 0.001 and 0.008 mg/ml, respectively. The relative standard deviation (R.S.D.) of each enantiomer did not exceed 0.90%. The method has been successfully applied to the determination of enantiomers in pharmaceuticals.