Determination of naftopidil enantiomers in rat plasma using chiral solid phases and pre-column derivatization high-performance liquid chromatography.

Two bioanalytical HPLC methods (chiral solid phases (CSPs) HPLC and pre-column derivatization HPLC) were developed and validated for the determination of naftopidil enantiomers in rat plasma. Analytes were extracted from biomaterials by liquid-liquid extraction. The pre-column derivatization HPLC method employed (+)-diacetyl-L-tartaric anhydride (DATAN) as the pre-column derivatization reagent, and subsequent separation of diastereomers was conducted on an Agilent Hypersil ODS column with a mixture of methanol-acetonitrile-phosphate buffer (pH 4.1; 20 mM) (40:30:30, v/v/v) flowing at 1 mL/min as the mobile phase. The CSPs HPLC method utilized a Chiralpak IA column with a mobile phase of methanol-acetonitrile-acetate buffer (pH 5.3; 5 mM) (50:25:25, v/v/v) flowing at 0.5 mL/min. In both methods, the analytes were monitored using a fluorescence detector with an excitation wavelength of 290 nm and an emission wavelength of 340 nm. Both methods were consistent (RSD<15% by the derivatization method and<10% by the CSPs method) and linear (r>9950). Compared to the pre-column derivatization method, the CSPs method had lower quantification limits (10.6/9.6 ng/mL of (+)-/(-)-naftopidil by derivatization method and 1.1/1.8 ng/mL of (+)-/(-)-naftopidil by CSPs method), and was simpler to carry out. The validated CSPs method was successfully applied in a pharmacokinetic study of naftopidil enantiomers in rats, which showed that pharmacokinetic parameters of (+)- and (-)-NAF after intravenous administration of (±)-NAF were similar.