Solution— Dilute a quantity of Suspension with a mixture of methanol and hydrochloric acid (99:1) to obtain a solution having a concentration of about 1 mg per mL. Filter the mixture, if necessary, to obtain a clear solution. Transfer 1 mL of this solution to a 100-mL volumetric flask, dilute with 0.1 N sodium hydroxide to volume, and mix.

Acidified methanol— Use a mixture of methanol and hydrochloric acid (99:1).

Mobile phase— Dissolve 11.0 g of monobasic sodium phosphate in 800 mL of water. Add 1200 mL of methanol, and mix. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Quantitatively dissolve an accurately weighed quantity of USP Albendazole RS in Acidified methanol to obtain a stock solution having a known concentration of about 1 mg per mL. Dilute an accurately measured volume of this stock solution with Mobile phase to obtain a solution having a known concentration of about 100 µg per mL.

Assay preparation— Transfer an accurately measured volume of Oral Suspension, equivalent to about 100 mg of albendazole, to a 100-mL volumetric flask, dilute with Acidified methanol to volume, and mix. Transfer 10.0 mL of this solution to a second 100-mL volumetric flask, dilute with Mobile phase to volume, and mix. Filter, if necessary, to obtain a clear solution.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 308-nm detector and a 4-mm × 25-cm column that contains packing L1. The flow rate is about 2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 2000 theoretical plates; 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 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 albendazole (C12H15N3O2S) in each mL of the Oral Suspension taken by the formula: in which C is the concentration, in µg per mL, of USP Albendazole RS in the Standard preparation; V is the volume, in mL, of Oral Suspension taken to prepare the Assay preparation; and rU and rS are the albendazole peak responses obtained from the Assay preparation and the Standard preparation, respectively.