Medium: 0.1 N hydrochloric acid containing 0.1% sodium lauryl sulfate; 900 mL.

Apparatus 2: 75 rpm.

Time: 60 minutes.

Standard solution— Prepare a solution of USP Spironolactone RS and USP Hydrochlorothiazide RS in a mixture of methanol and Dissolution Medium (1:1) having accurately known concentrations of about 0.0125 mg of each per mL.

Test solution— Transfer a 5.0-mL portion of the solution under test to a 10-mL volumetric flask, dilute with methanol to volume, and mix.

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

Tolerances— Not less than 75% (Q) of each of the labeled amounts of C24H32O4S and C7H8ClN3O4S2 is dissolved in 60 minutes.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (7:3). Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard preparation— Dissolve accurately weighed quantities of USP Spironolactone RS and USP Hydrochlorothiazide RS in methanol to obtain a solution having known concentrations of about 50 µg of each per mL.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 25 mg of spironolactone, to a 100-mL volumetric flask, add about 70 mL of methanol, shake by mechanical means for 30 minutes, dilute with methanol to volume, mix, and centrifuge. Transfer 20.0 mL of the resultant clear liquid to a 100-mL volumetric flask, dilute with methanol to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the resolution, R, between hydrochlorothiazide and spironolactone 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 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The relative retention times are about 0.5 for hydrochlorothiazide and 1.0 for spironolactone. Calculate the quantity, in mg, of spironolactone (C24H32O4S) in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Spironolactone RS in the Standard preparation; and rU and rS are the responses of the spironolactone peak obtained from the Assay preparation and the Standard preparation, respectively. Calculate the quantity, in mg, of hydrochlorothiazide (C7H8ClN3O4S2) by the same formula, changing the terms to refer to hydrochlorothiazide.