Assay:
Determine by liquid chromatography
Solvent
mixture: 50 volumes of mobile phase and 50 volumes of methanol.
Test
solution: Weigh and powder 20 tablets. Disperse a quantity of powder containing
about 50 mg of Sildenafil with 35 ml of solvent mixture, sonicate for 20
minutes and dilute to 50.0 ml with the solvent mixture, filter. Further dilute
5 ml to 50 ml with solvent mixture.
Reference solution:(Standard solution) : A 0.14 per cent w/v solution of
Sildenafil citrate RS in the solvent mixture. Further dilute 5 ml to 50 ml with
solvent mixture.
Chromatographic
system
- Column : a
stainless steel column 25 cm x 4.6 mm, packed with silica (5 µm) (Such as
Zobrax Eclipse XBD C18),
- Mobile phase: a
mixture of 30 volumes of solution containing 3.85 g of ammonium acetate and 1.0
ml of triethylamine in 1000 ml of water, adjust to pH 5.5 with acetic acid and
70 volumes of methanol,
- Flow rate: 1 ml
per minute.
- Spectrophotometer
set as 294 nm,
- Injection volume
20 µl.
Inject the reference solution. The test is not valid unless the
theoretical plates is not less than 2000, the tailing factor is not more than
2.0 and the relative standard deviation for replicate injections is not more than
5.0 per cent.
Inject the reference solution, the test solution.
Calculate the content of C28H38N6O11S in the tablet.
