Assay
Mobile phase
Prepare a filtered and degassed mixture of methanol and 0.05
Mmonobasic potassium phosphate (350:300).Make adjustments if necessary (see
System Suitabilityunder
Chromatography á621ñ).
Internal standard solution
Dissolve a quantity of betamethasone in methanol to obtain a solution containing about 0.4mg per mL.
Standard preparation
Dissolve an accurately weighed quantity of
USP Prednisone RSin methanol,and dilute quantitatively,and stepwise if necessary,with methanol to obtain a solution having a known concentration of about 0.25mg per mL.Transfer 10.0mLof this solution to a 50-mLvolumetric flask.Add 10.0mLof
Internal standard solution,dilute with methanol to volume,and mix.
Assay preparation
Transfer an accurately measured volume of well-mixed Suspension,equivalent to about 80mg of prednisone,to a 100-mLvolumetric flask.Dilute with methanol to volume,and mix.Transfer 3.0mLof this solution to a 50-mLvolumetric flask.Add 10.0mLof Internal standard solution,dilute with methanol to volume,and mix.
Chromatographic system
(see
Chromatography á621ñ)The liquid chromatograph is equipped with a 254-nm detector and a 4-mm ×30-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the
Standard preparation,and record the peak responses as directed for
Procedure:the relative retention times are about 1.9for betamethasone and 1.0for prednisone,the resolution,
R,between the prednisone peak and the betamethasone peak is not less than 3.5,and the relative standard deviation for replicate injections is not more than 2.0%.
Procedure
Separately inject equal volumes (about 10µL)of the
Standard preparationand the
Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the analyte peaks.Calculate the quantity,in mg,of prednisone in each mLof the Suspension taken by the formula:
5000(C/3V)(RU/RS),
in which
Cis the concentration,in mg per mL,of
USP Prednisone RSin the
Standard preparation,
Vis the volume,in mL,of the Suspension taken to prepare the
Assay preparation,and
RUand
RSare the ratios of the prednisone peak to the internal standard peak obtained from the
Assay preparationand the
Standard preparation,respectively.