[High performance liquid chromatographic separation of oxybutynin enantiomers using chiral mobile phase additive]

A simple and effective method for the separation of oxybutynin enantiomers was developed using high performance liquid chromatography with hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral mobile phase additive and a C18 reversed-phase column as the stationary phase. beta-CD and HP-beta-CD were investigated as chiral mobile phase additives separately. The results showed that oxybutynin enantiomers could not be separated when adding beta-CD in the mobile phase, but optimal resolution was obtained when using HP-beta-CD as the chiral mobile phase additive. Excellent enantioseparation was achieved with the mobile phase composed of 30 mmol/L KH2PO4-acetonitrile(80:20, v/v) mixed with 60 mmol/L HP-beta-CD at pH 4.0. The detection wavelength was set at 223 nm and the column temperature was set at 28 degrees C with a flow rate of 0.8 mL/min. Under the optimized conditions, the resolution of enantiomers was 1.54 and the limit of quantitation was 1.0 ng. Comparing with chiral stationary phase chromatography, the method was simple, economic and considerably reproducible.