A: Infrared Absorption 197K.

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.

Mobile phase, Chromatographic system, and Procedure— Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Didanosine Related Compound A RS in water to obtain a solution containing 5 µg per mL. Make stepwise dilutions if necessary. [note—Use this solution within 48 hours of preparation.]

Test solution— Transfer the contents of 1 container of Didanosine for Oral Solution to a suitable volumetric flask, and dissolve in water to obtain a solution having a concentration of approximately 4 mg per mL. [note—Use this solution within 24 hours of preparation.]

Diluted test solution— Dilute the Test solution quantitatively, and stepwise if necessary, with water to obtain a solution having a concentration of about 0.1 mg per mL.

0.01 M Ammonium acetate buffer solution— Dissolve 1.54 g of ammonium acetate into a 2000-mL volumetric flask, dilute with water to volume, mix, and pass through a 0.45-µm filter.

Standard preparation— Dissolve an accurately weighed quantity of USP Didanosine RS in water to obtain a solution containing 0.1 mg per mL. [note—Use this solution within 24 hours of preparation.]

Assay preparation— Transfer the contents of 1 bottle of Didanosine for Oral Solution to a suitable volumetric flask and dilute stepwise, if necessary, to obtain a solution in water of about 0.1 mg per mL. [note—Use this solution within 24 hours of preparation.]

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector, a 4-mm × 25-cm analytical column containing packing L1, and a 4.6- × 20-mm guard column. The flow rate is about 2.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the retention time for didanosine is between 7 and 11 minutes; the column efficiency is not less than 6000 theoretical plates; and the relative standard deviation for replicate injections is not more than 1.5%.

Procedure— Separately inject equal volumes (about 20 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 didanosine (C10H12N4O3) in the portion of Didanosine for Oral Solution taken by the formula: in which C is the concentration, in mg per mL, of USP Didanosine RS in the Standard preparation; D is the volume, in mL, of Didanosine for Oral Solution used to prepare the Assay preparation multiplied by the dilution factor of the Assay preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.