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Development and Validation of a New Stereoselective RP-HPLC Method for Simultaneous Quantification of Tadalafil, its One Enantiomer, and Two Diastereomers in API and Tablet Form

Abstract A new, simple, and stereoselective RP-HPLC method was developed and validated for the simultaneous quantification of tadalafil, its one enantiomer, and two diastereomers in API and tablets. Using varied compositions of water, acetonitrile, and acetic acid as mobile phases in gradient mode at a 0.40 mL/min flow rate and detection at 285 nm, all this separation was achieved on the Lux Cellulose-3 (150 mm x 4.6 mm, 3 µm) column at a 30.0°C oven temperature. All isomers were eluted within 24 minutes, with a resolution of more than 2.3 between any two isomers. With 10.0 µL injection volume, the LOD and LOQ were determined to be 0.06 µg/mL and 0.10 µg/mL, respectively. The linearity of tadalafil (0.10-400 µg/mL), one enantiomer, and two diastereomers (0.10-4.0 µg/mL) was confirmed with a correlation coefficient of 0.999. The forced degradation study revealed the specificity for all the peaks as well as the conversion of tadalafil into diastereomers (6S, 12aR) in acidic conditions and into diastereomers (6R, 12aS) in alkaline conditions. At lower concentrations, the recoveries for all isomers ranged from 100.0 ± 15.0%, while the assay values for tadalafil were within 100.0 ± 2.0%. According to the validation outcome as per ICH guidelines, the proposed method is an accurate, precise, linear, and robust stereoselective method for simultaneous quantification. GRAPHICAL ABSTRACT