A:Infrared Absorption á197Kñ .

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 under Assay and limit for guanine.

Test solution: dimethyl sulfoxide.

Standard solution: dimethyl sulfoxide.

Eluant: a mixture of chloroform,methanol,and ammonium hydroxide (80:20:2).

Visualization: 1.

Application volume: 5µL.

Limit: 1%.

Solvent— Use dimethyl sulfoxide.

Change to read:

Mobile phase— Prepare a filtered and degassed solution of glacial acetic acid in water (1in 1000).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

System suitability solution 1— Dissolve accurately weighed quantities of USP Acyclovir RSand guanine in 0.1Nsodium hydroxide,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having known concentrations of about 0.1mg of each per mL.

System suitability solution 2— Dissolve an accurately weighed quantity of guanine in 0.1Nsodium hydroxide,and dilute quantitatively,and stepwise if necessary,with water to obtain a solution having a known concentration of about 0.7µg per mL.USP28

Guanine standard preparation— Transfer about 8.75mg of guanine,accurately weighed,to a 500-mLvolumetric flask.Dissolve in 50mLof 0.1Nsodium hydroxide,dilute with water to volume,and mix.Transfer 2.0mLof this solution to a 50-mLvolumetric flask,dilute with 0.01Nsodium hydroxide to volume,and mix to obtain a solution having a known concentration of about 0.7µg per mL.USP28

Standard preparation— Dissolve about 25mg of USP Acyclovir RS,accurately weighed,in 5mLof 0.1Nsodium hydroxide in a 50-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution USP28to a 50-mLvolumetric flask,dilute with 0.01Nsodium hydroxide to volume,and mix to obtain a solution having a known concentration of about 0.1mg of USP Acyclovir RSper mL.USP28

Assay preparation— Dissolve about 100mg of Acyclovir,accurately weighed,in 20mLof 0.1Nsodium hydroxide in a 200-mLvolumetric flask,dilute with water to volume,and mix.Transfer 10.0mLof this solution to a 50-mLvolumetric flask,dilute with 0.01Nsodium hydroxide to volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 254-nm detector and a 4.2-mm ×30-cm column that contains packing L1.The flow rate is about 3mLper minute.Chromatograph System suitability solution 1,USP28and record the peak responses as directed for Procedure:the resolution,R,between acyclovir and guanine is not less than 2.0;the tailing factor for the analyte peak is not more than 2;and the relative standard deviation for replicate injections for the acyclovir peakUSP28is not more than 2.0%.Chromatograph System suitability solution 2,and record the peak responses as directed for Procedure:the relative standard deviation for replicate injections is not more than 2.0%.USP28

Procedure— Separately inject equal volumes (about 20µL)of the Standard preparation,Guanine standard preparation,USP28and the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for all the peaks.Calculate the quantity,in µg,of guanine in the portion of Acyclovir taken by the formula: in which Cis the concentration,in µg per mL,of guanine in the Guanine standard preparation;USP28and rUand rSare the peak responses due to guanine in the Assay preparationand the Guanine standard preparation,USP28respectively:not more than 0.7%of guanine is found.Calculate the quantity,in mg,of C8H11N5O3in the portion of Acyclovir taken by the formula: in which Cis the concentration,in mg per mL,of USP Acyclovir RSin the Standard preparation;and rUand rSare the peak responses due to acyclovir in the Assay preparationand the Standard preparation,respectively.