Medium: 0.1 N hydrochloric acid; 1000 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Mobile phase and Chromatographic system— Prepare as directed in the Assay.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and filtered portions of the solutions under test into the chromatograph, record the chromatograms, and measure the areas for the major peaks. Calculate the quantities of irbesartan (C25H28N6O) and hydrochlorothiazide (C7H8ClN3O4S2) dissolved in comparison with a Standard solution having known concentrations of USP Irbesartan RS and USP Hydrochlorothiazide RS in the same Medium and similarly chromatographed.

Tolerances— Not less than 80% (Q) of the labeled amounts of C25H28N6O and C7H8ClN3O4S2 are dissolved in 30 minutes.

Triethylamine solution— Add 1.0 mL of triethylamine to 1000 mL of water, mix, and adjust with phosphoric acid to a pH of 3.5.

Mobile phase— Prepare a filtered and degassed mixture of Triethylamine solution and acetonitrile (1:1). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Transfer about 25 mg of USP Hydrochlorothiazide RS, accurately weighed, to a 100-mL volumetric flask. Add 25J mg of USP Irbesartan RS, accurately weighed, J being the ratio of the labeled amount, in mg, of irbesartan to the labeled amount, in mg, of hydrochlorothiazide per Tablet. Dissolve in and dilute with Mobile phase to volume, and mix.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of powder, equivalent to about 25 mg of hydrochlorothiazide, to a 100-mL volumetric flask. Add about 80 mL of Mobile phase, and stir on a magnetic stir plate for 15 minutes. Dilute with Mobile phase to volume, and mix. Centrifuge a portion of this solution for 10 minutes, and use the clear supernatant.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak areas as directed for Procedure: the resolution, R, between hydrochlorothiazide and irbesartan is not less 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, and record the areas for the major peaks. Calculate the quantities, in mg, of irbesartan (C25H28N6O) and hydrochlorothiazide (C7H8ClN3O4S2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of the appropriate USP Reference Standard in the Standard preparation; and rU and rS are the peak responses of the corresponding analyte obtained from the Assay preparation and the Standard preparation, respectively.