A: Thin-Layer Chromatographic Identification Test á201ñ—

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

Mobile phase— Prepare a filtered and degassed mixture of water and acetonitrile (70:30).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution— Prepare a solution in Mobile phasecontaining in each mLabout 0.3mg of USP Dexamethasone RS,1.35mg of benzyl alcohol,0.27mg of methylparaben,and 0.03mg of propylparaben.

Standard preparation— Quantitatively dissolve an accurately weighed amount of USP Dexamethasone RSin methanol to obtain a stock solution having a known concentration of about 7.5mg per mL.Transfer 4.0mLto a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix to obtain a solution having a known concentration of about 0.3mg of USP Dexamethasone RSper mL.

Assay preparation— Transfer an accurately measured volume of Injection,equivalent to about 30mg of dexamethasone,to a 100-mLvolumetric flask,dilute with Mobile phaseto 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-µm packing L7.The flow rate is about 2mLper minute.Chromatograph the System suitability solution,and record the peak responses as directed for Procedure:the relative retention times are about 0.4for benzyl alcohol,0.5for methylparaben,1.0for dexamethasone,and 1.4for propylparaben;and the resolution,R,between the neighboring peaks for benzyl alcohol and methylparaben,methylparaben and dexamethasone,and dexamethasone and propylparaben is not less than 3.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the peak responses for dexamethasone.Calculate the quantity,in mg,of dexamethasone (C22H29FO5)in each mLof the Injection taken by the formula: in which Cis the concentration,in mg per mL,of USP Dexamethasone RSin the Standard preparation;Vis the volume,in mL,of Injection taken;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.