A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that 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 and a Standard solution of USP Amiloride Hydrochloride RS in methanol, containing 0.2 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 value of the principal spot in the chromatogram of the test solution corresponds to that obtained from the Standard solution.

Medium: 0.1 N hydrochloric acid; 900 mL.

Apparatus 2: 50 rpm.

Time: 30 minutes.

Procedure— Determine the amount of C6H8ClN7O·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 363 nm on filtered portions of the solution under test, suitably diluted with 0.1 N hydrochloric acid, in comparison with a Standard solution having a known concentration of USP Amiloride Hydrochloride RS in the same Medium. An amount of methanol not to exceed 2% of the total volume of the Standard solution may be used to dissolve the amiloride hydrochloride.

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

Procedure for content uniformity— Transfer 1 finely powdered Tablet to a 100-mL volumetric flask, add 60 mL of 0.1 N hydrochloric acid, and shake by mechanical means for 30 minutes. Dilute with 0.1 N hydrochloric acid to volume, mix, and centrifuge a portion of the mixture. Dilute an accurately measured portion of the clear supernatant quantitatively to obtain a solution containing about 10 µg of amiloride hydrochloride per mL. Concomitantly determine the absorbances of this solution and a Standard solution of USP Amiloride Hydrochloride RS in the same medium having a known concentration of about 10 µg per mL, at the wavelength of maximum absorbance at about 363 nm, with a suitable spectrophotometer, using 0.1 N hydrochloric acid as the blank. Calculate the quantity, in mg, of C6H8ClN7O·HCl in the Tablet taken by the formula: in which T is the labeled quantity, in mg, of amiloride hydrochloride in the Tablet, C is the concentration, in µg per mL, of USP Amiloride Hydrochloride RS, corrected for loss in weight in the Standard solution; D is the concentration, in µg per mL, of amiloride hydrochloride in the solution from the Tablet, based upon the labeled quantity per Tablet and the extent of dilution; and AU and AS are the absorbances of the solution from the Tablets and the Standard solution, respectively.

Buffer solution— Dissolve 136 g of monobasic potassium phosphate in 800 mL of water, and adjust by the addition of phosphoric acid, with mixing, to a pH of 3.0. Dilute with water to 1000 mL, and mix.

Mobile phase— Prepare a suitable degassed mixture of water, methanol, and Buffer solution (71:25:4).

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 5.0 mL of the solution to a 50-mL volumetric flask, and add 10.0 mL of methanol and 2.0 mL of 0.1 N hydrochloric acid. Dilute with water to volume, and mix. The concentration of USP Amiloride Hydrochloride RS in the Standard preparation is about 0.1 mg per mL.

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 containing 15.0 mL of methanol and 2.0 mL of 0.1 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 tailing factor of the major peak is not more 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 obtained from the Assay preparation and the Standard preparation, respectively.