Mobile phase— Prepare a solution of 0.01 M dibutylamine in 0.025 M aqueous monobasic sodium phosphate dihydrate and acetonitrile (75:25). Adjust Mobile phase with 1 N sodium hydroxide to a pH of 8.0, filter, and degas. Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Dissolve an accurately weighed quantity of N-hydroxymethylsumatriptan succinate in Mobile phase to obtain a known concentration of about 3.0 mg per mL.

Standard stock preparation— Dissolve an accurately weighed quantity of USP Sumatriptan Succinate RS in Mobile phase to obtain a known concentration of about 4.0 mg per mL.

Standard preparation— Dilute the Standard stock preparation with Mobile phase to obtain a solution having a known concentration of about 120 µg per mL. Each solution contains 30 µg per mL of Internal standard solution.

Assay preparation— Transfer about 1 mL of Oral Suspension from each bottle to a suitable container, and dilute with 0.1 M hydrochloric acid to obtain a concentration of about 0.15 mg per mL. Pass the solution through a 0.22-µm syringe filter into a 0.3-mL polypropylene sample vial for assay.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 282-nm detector and a 4.6-mm ×10-cm analytical column that contains 5-µm packing L1. The flow rate is about 1.5 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the retention times for sumatriptan and N-hydroxymethylsumatriptan are 11 and 14 minutes, respectively; and the relative standard deviation for replicate injections is not more than 1.5%.

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 sumatriptan succinate (C14H21N3O2S·C4H6O4) in the volume of Oral Suspension taken by the formula: in which C is the concentration, in mg per mL, of USP Sumatriptan Succinate RS in the Standard preparation; V is the volume, in mL, of Oral Suspension taken; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.