An enantiospecific HPLC method for the determination of (S)-enantiomer impurities in (R)-tolterodine tartarate.

A high-performance liquid chromatographic method was developed for the separation of the enantiomers of tolterodine tartarate. The proposed method was applied to the determination of (S)-isomer in (R)-tolterodine tartarate, and satisfactory results were obtained. The enantiomers of tolterodine tartarate were separated on a Chiralpak AD-H (250 mm x 4.6 mm) column containing amylose tris-(3,5-dimethylphenyl-carbamate) at room temperature. The mobile phase consisted of n-hexane and isopropyl alcohol in the ratio of 85:15 (v/v) with 0.075% triethylamine (TEA) and 0.05% trifluoroacetic acid (TFA) as the additive. The flow rate was kept at 0.5 ml/min, and UV detection wavelength was set at 283 nm. The calibration curves of (S)-enantiomer in the concentration range from 0.05 microg/ml to 1 microg/ml range were linear. The relative standard deviations of within-day and between-day were less than 2% (n = 3). The limit of detection (LOD) was 0.75 ng (S/N = 3) and the limit of quantification (LOQ) was 0.05 microg/ml (RSD < 4.1%, n = 3). The determination recoveries of the (S)-enantiomer were in the range of 98.2-104.8%. The results demonstrated that the developed HPLC method was a reliable, simple technique and was applicable to the purity determination of (R)- tolterodine tartarate.