A: Prepare a test solution in methanol containing 5 mg per mL. Separately apply 5 µL of this solution and 5 µL of a Standard solution of USP Zidovudine RS in a mixture of methanol and water (75:25) containing 5 mg per mL to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture containing a fluorescent indicator having an optimal intensity at 254 nm. 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 UV light: the RF value 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 preparation corresponds 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 C standard stock solution, and Chromatographic system— Proceed as directed in the Assay.

Standard solution— Proceed as directed for Standard preparation in the Assay.

Test solution— Proceed as directed for Assay preparation in the Assay.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into 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 C is the concentration, in mg per mL, of USP Zidovudine Related Compound C RS in the Standard solution; rU and rS are the peak responses of zidovudine related compound C (thymine) obtained from the Test solution and the Standard solution, respectively; and Q is 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 0.040 M sodium acetate, methanol, acetonitrile, and glacial acetic acid (900:90:10:2). Make adjustments if necessary (see System Suitability under Chromatography 621).

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

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

Standard preparation— Transfer 10.0 mL of the Standard stock solution and 2.0 mL of the Zidovudine related compound C standard stock solution to a 100-mL volumetric flask, dilute with Mobile phase to volume, and mix.

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

Chromatographic system (see Chromatography 621)— 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 1.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.12 for zidovudine related compound C (thymine) and 1.0 for 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 10 µL) of the Standard preparation and the Assay preparation into 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 C is the concentration, in mg per mL, of USP Zidovudine RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.