A: Tablets respond to Identification test A under Diltiazem Hydrochloride Extended-Release Capsules.

B: 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.

Medium: water; 900 mL.

Apparatus 2: 75 rpm.

Times: 30 minutes and 3 hours.

Procedure— Determine the amount of C22H26N2O4S·HCl dissolved from UV absorbances at the wavelength of maximum absorbance at about 240 nm using filtered portions of the solution under test, suitably diluted with water, if necessary, in comparison with a Standard solution having a known concentration of USP Diltiazem Hydrochloride RS in the same Medium.

Tolerances— Use the following acceptance criteria for the 30-minute time point: at S1 no unit is more than Q; at S2 the average value is equal to or less than Q, and no unit is greater than Q + 10%; at S3 the average value is equal to or less than Q, and not more than 2 units are more than Q + 10%, and no unit is more than Q + 25%. Use the criteria in the Acceptance Table under Dissolution 711 for the 3-hour time point. Not more than 60% (Q) of the labeled amount of C22H26N2O4S·HCl is dissolved in 30 minutes, and not less than 75% (Q) is dissolved in 3 hours.

Buffer, Mobile phase, Standard preparation, System suitability preparation, Chromatographic system, and Procedure— Proceed as directed in the Assay under Diltiazem Hydrochloride.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 600 mg of diltiazem hydrochloride to a 500-mL volumetric flask. Add 200 mL of methanol, sonicate for 1 hour, cool, dilute with methanol to volume, and mix. Centrifuge a 25-mL aliquot at 3500 rpm for 15 minutes, and use the clear supernatant for injection into the liquid chromatograph.

Procedure— Calculate the quantity, in mg, of C22H26N2O4S·HCl in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Diltiazem Hydrochloride RS in the Standard preparation; and rU and rS are the diltiazem hydrochloride peak areas in the Assay preparation and the Standard preparation, respectively.