A: It meets the requirements under Thin-Layer Chromatographic Identification Test á201BNPñ.

B: The retention time of the major peak for dexamethasone in the chromatogram of the Assay preparationcorresponds to that in the chromatogram of theStandard preparation,as obtained in theAssay for dexamethasone.

Mobile phase— Prepare a suitable aqueous solution of acetonitrile,approximately 1in 3,such that the retention time of dexamethasone is about 5minutes.

Standard preparation— Dissolve an accurately weighed quantity of USP Dexamethasone RSin a mixture of acetonitrile and methanol (1:1)to obtain a solution having a known concentration of about 60µg per mL.

Assay preparation— Transfer an accurately weighed portion of Ophthalmic Ointment,equivalent to about 3mg of dexamethasone,to a suitable test tube,add about 15mLof cyclohexane,and heat in a water bath at 75±5for 10minutes.[NOTE—If the ointment is not fully dissolved,heat on a steam bath for about 30seconds,place a cap on the test tube,and place on a vortex mixer until all solid material is dissolved.]Filter with suction through a medium-porosity sintered-glass filter.Rinse the test tube twice with 10-mLportions of cyclohexane,filtering the rinsings through the filter,and discard the filtrates.Wash the filter with about 10mLof a mixture of acetonitrile and methanol (1:1),and collect the filtrate in a 50-mLbeaker.Wash the test tube and the filter with several 10-mLportions of the same solvent,and combine the washings in the 50-mLbeaker.Transfer the contents of the beaker to a 50-mLvolumetric flask,with the aid of a mixture of acetonitrile and methanol (1:1),dilute with the same solvent to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm ×25-cm column that contains 5-to 10-µm packing L1.The flow rate is about 2mLper minute.Chromatograph theStandard preparation,and record the peak response as directed underProcedure:the column efficiency is not less than 4000theoretical plates,and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 10µL)of theStandard preparation and theAssay preparation into the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C22H29FO5in the portion of Ophthalmic Ointment taken by the formula: in whichCis the concentration,in µg per mL,of USP Dexamethasone RSin theStandard preparation;andrUandrSare the peak responses of theAssay preparation and theStandard preparation,respectively.