by Related substances (by HPLC)
Preparation of Buffer solution: Dilute 1.6 ml of orthophosphorous acid in 1000 ml of water, adjust the pH to 2.9 with triethylamine.
Mobile phase preparation: Buffer: Acetonitrile (60:40).
Standard preparation: Accurately weigh about 25 mg of Tadalafil WS in to a 100 ml of volumetric flask. Dissolve in the mobile phase and make up to the volume up to 100 ml with mobile phase.
Test preparation: Accurately weigh about equivalent to 25 mg of the test sample in to a 100 ml of volumetric flask. Dissolve in the mobile phase and make up to the volume up to 100 ml with mobile phase.
Chromatographic conditions:
Column: C18, 150 mm x 4.6 mm; 5µ.
Detector: UV 220 nm.
Flow rate: 1.0 ml per minute.
Runtime: 50 minutes.
Column temperature: 30°C.
Injection volume: 10µl.
System suitability: Relative standard deviation (RSD) is not more than 2.0%.
Procedure: Separately inject five replicate injection for standard preparation and inject two replicate injection for test preparation and calculate the results by comparison, record the chromatograms and measure the responses for the major peaks.
Calculation: Calculate the individual impurity and total impurities, by using given below formula:
Area of individual impurity Std. dilution Average wt.
Individual impurity = ———————————- x —————— x ——————— x 100
Area of std. Test dilution Assay (in mg)
Area of total impurities Std. dilution Average wt.
Total impurities = ———————————- x —————— x ——————— x 100
Area of std. Test dilution Assay (in mg)
