A: Prepare a test solution in methanol containing 5mg per mL.Separately apply 5µLof this solution and 5µLof a Standard solution of USP Zidovudine RSin a mixture of methanol and water (75:25)containing 5mg per mLto a thin-layer chromatographic plate (see Chromatography á621ñ)coated with a 0.25-mm layer of chromatographic silica gel mixture containing a fluorescent indicator having an optimal intensity at 254nm.Allow the applications to dry,and develop the chromatogram in a solvent system consisting of butyl alcohol,n-heptane,acetone,and ammonium hydroxide (40:30:30:10)until the solvent front has moved about three-fourths of the length of the plate.Remove the plate from the developing chamber,mark the solvent front,and allow the solvent to evaporate.Observe the plate under short-wavelength UVlight:the RFvalue of the principal spot obtained from the test solution corresponds to that of the principal spot obtained from the Standard solution.

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.

FOR ORAL SOLUTION PACKAGED IN SINGLE-UNIT CONTAINERS: meets the requirements.

FOR ORAL SOLUTION PACKAGED IN MULTIPLE-UNIT CONTAINERS: meets the requirements.

Mobile phase,Standard stock solution,Zidovudine related compound Cstandard stock solution,and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Proceed as directed for Standard preparationin the Assay.

Test solution— Proceed as directed for Assay preparationin the Assay.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses.Calculate the quantity,in mg,of zidovudine related compound C(thymine)in the volume of Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Zidovudine Related Compound C RSin the Standard solution;rUand rSare the peak responses of zidovudine related compound C(thymine)obtained from the Test solutionand the Standard solution,respectively;and Qis the quantity,in mg,of zidovudine in the volume of Oral Solution taken,as determined in the Assay:not more than 3.0%is found.

Mobile phase— Prepare a filtered and degassed mixture of 0.040Msodium acetate,methanol,acetonitrile,and glacial acetic acid (900:90:10:2).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard stock solution— Dissolve an accurately weighed quantity of USP Zidovudine RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 1.0mg per mL.

Zidovudine related compound Cstandard stock solution— Transfer about 20mg of USP Zidovudine Related Compound C RS,accurately weighed,to a 200-mLvolumetric flask,add 150mLof Mobile phase,sonicate for 10minutes,dilute with Mobile phaseto volume,and mix.

Standard preparation— Transfer 10.0mLof the Standard stock solutionand 2.0mLof the Zidovudine related compound Cstandard stock solutionto a 100-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Assay preparation— Transfer an accurately measured volume of Oral Solution,equivalent to about 100mg of zidovudine,to a 100-mLvolumetric flask;dissolve in and dilute with Mobile phaseto volume;and mix.Transfer 5.0mLof this solution to a 50-mLvolumetric flask,dilute with Mobile phaseto volume,and mix.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 240-nm detector and a 4.0-mm ×12.5-cm column that contains packing L1.The flow rate is about 1.0mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the relative retention times are about 0.12for zidovudine related compound C(thymine)and 1.0for zidovudine;the resolution,R,between zidovudine and zidovudine related compound C(thymine)is not less than 4.0;the tailing factor is not more than 2.0;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 major peaks.Calculate the quantity,in mg,of zidovudine (C10H13N5O4)in the portion of Oral Solution taken by the formula: in which Cis the concentration,in mg per mL,of USP Zidovudine RSin the Standard preparation;and rUand rSare the peak responses obtained from the Assay preparationand the Standard preparation,respectively.