A: The retention times of the major peaks in the chromatogram of the Assay preparation correspond to those in the chromatogram of the Standard preparation, as obtained in the Assay.

B: Transfer an amount of finely ground Tablets, equivalent to 5 mg of amiloride hydrochloride, to a 25-mL volumetric flask, add methanol to volume, mix, and filter. Separately apply 10 µL each of the filtrate, a Standard solution of USP Amiloride Hydrochloride RS in methanol containing 0.2 mg per mL, and a Standard solution of USP Hydrochlorothiazide RS in methanol containing 2 mg per mL to a thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel mixture. Develop the chromatogram in a solvent system consisting of a mixture of tetrahydrofuran and 3 N ammonium hydroxide (22:3) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, air-dry, and examine under short-wavelength UV light: the RF values of the amiloride hydrochloride and hydrochlorothiazide spots obtained from the test solution correspond to those obtained from the corresponding Standard solutions.

Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

spectrophotometric procedure—

chromatographic procedure—

Tolerances— Not less than 80% (Q) of the labeled amount of C6H8ClN7O·HCl and 75% (Q) of the labeled amount of C7H8ClN3O4S2 are dissolved in 30 minutes.

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

Test solution— Proceed as directed for Assay preparation in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Benzothiadiazine Related Compound A RS in Mobile phase to obtain a solution having a known concentration of about 10 µg per mL.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in µg, of benzothiadiazine related compound A in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of USP Benzothiadiazine Related Compound A RS in the Standard solution; and rU and rS are the peak responses of benzothiadiazine related compound A obtained from the Test solution and the Standard solution, respectively: not more than 1.0% is present.

Buffer solution and Mobile phase— Prepare as directed in the Assay under Amiloride Hydrochloride Tablets.

Standard preparation— Dissolve a suitable quantity of USP Amiloride Hydrochloride RS in methanol to obtain a solution having a known concentration of about 1.0 mg of amiloride hydrochloride per mL. Transfer 10.0 mL of this solution to a 100-mL volumetric flask containing 100 mg of USP Hydrochlorothiazide RS, accurately weighed, and 20.0 mL of methanol. Add 4.0 mL of 1 N hydrochloric acid, dilute with water to volume, and mix. The concentrations of USP Amiloride Hydrochloride RS and USP Hydrochlorothiazide RS in the Standard preparation are about 0.1 mg per mL and 1 mg per mL, respectively.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 5 mg of amiloride hydrochloride, to a 50-mL volumetric flask. Add 15.0 mL of methanol, and 2.0 mL of 1 N hydrochloric acid. Sonicate for 10 minutes, dilute with water to volume, sonicate for an additional 10 minutes, mix, and filter.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 286-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph five replicate injections of the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.7 for hydrochlorothiazide and 1.0 for amiloride hydrochloride; the resolution, R, between hydrochlorothiazide and amiloride hydrochloride is not less than 2.0; and the relative standard deviation 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. Calculate the quantity, in mg, of amiloride hydrochloride (C6H8ClN7O·HCl) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Amiloride Hydrochloride RS, corrected for loss in weight in the Standard preparation; and rU and rS are the peak responses for amiloride hydrochloride obtained from the Assay preparation and the Standard preparation, respectively. Similarly calculate the quantity, in mg, of hydrochlorothiazide (C7H8ClN3O4S2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Hydrochlorothiazide RS in the Standard preparation; and rU and rS are the peak responses of hydrochlorothiazide obtained from the Assay preparation and the Standard preparation, respectively.