A:Infrared Absorption á197Kñ.

B:Ultraviolet Absorption á197Uñ—

Mobile phase,System suitability solution,and Chromatographic system— Proceed as directed in theAssay.

Test solution— Transfer about 11mg of Ganciclovir,accurately weighed,to a 50-mLvolumetric flask;dissolve in and dilute withMobile phaseto volume;and mix.

Procedure— Inject a volume (about 20µL)of theTest solutioninto the chromatograph,record the chromatogram,and measure the peak responses.Calculate the percentage of each impurity in the portion of Ganciclovir taken by the formula: in which riis the peak response for each impurity in theTest solution;and rsis the sum of the responses of all the peaks:not more than 0.5%of ganciclovir related compound Ais found;and not more than 1.5%of total impurities is found.

Trifluoroacetic acid solution— Transfer about 0.5mLof trifluoroacetic acid to a 1000-mLvolumetric flask,dilute with water to volume,and mix.

Mobile phase— Prepare a filtered and degassed mixture ofTrifluoroacetic acid solutionand acetonitrile (1:1).Make adjustments if necessary (seeSystem SuitabilityunderChromatography á621ñ).

System suitability solution— Dissolve accurately weighed quantities of USP Ganciclovir RSand USP Ganciclovir Related Compound A RSinMobile phase,sonicating if necessary,to obtain a solution having a known concentration of about 0.1mg of each per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Ganciclovir RS,previously dried under vacuum at 80for 3hours,inMobile phase;and dilute quantitatively,and stepwise if necessary,withMobile phaseto obtain a solution having a known concentration of about 0.22mg per mL.

Assay preparation— Transfer about 11mg of Ganciclovir,previously dried under vacuum at 80for 3hours and accurately weighed,to a 50-mLvolumetric flask;dissolve in and dilute withMobile 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 packing L9.The flow rate is about 1.5mLper minute.The column temperature is 40.Chromatograph theSystem suitability solution,and record the peak responses as directed forProcedure:the relative retention times are about 0.9for ganciclovir related compound Aand 1.0for ganciclovir;the resolution,R,between ganciclovir and ganciclovir related compound Ais not less than 1.4;the column efficiency is not less than 5000theoretical plates;the tailing factor is not more than 1.4;and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 20µL)of theStandard preparationand theAssay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C9H13N5O4in the portion of Ganciclovir taken by the formula: in which Cis the concentration,in mg per mL,of USP Ganciclovir RSin theStandard preparation;and rUand rSare the peak responses obtained from theAssay preparationand theStandard preparation,respectively.