Medium: water; 500 mL.

Apparatus 2: 50 rpm.

Times: 1, 2, 4, and 6 hours.

pH 3.0 Buffer solution— Add 6.6 g of ammonium sulfate, accurately weighed, to 500 mL of water. Adjust with 1 N sulfuric acid to a pH of 3.0.

Mobile phase— Prepare a filtered and degassed mixture of methanol and pH 3.0 Buffer solution (50:50). Make adjustments if necessary (see System Suitability under Chromatography 621).

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with an UV wavelength detector and a 5-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph a Standard solution of USP Diluted Isosorbide Dinitrate RS in the same Medium, and record the chromatograms as directed for Procedure: the tailing factor is not more than 2.5, and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of a filtered portion of the solution under test, and record the chromatograms. Determine the amount of C6H8N2O8 dissolved in comparison with a Standard solution of USP Diluted Isosorbide Dinitrate RS in the same medium, similarly chromatographed.

Tolerances— The percentages of the labeled amount of C6H8N2O8 dissolved at the times specified conform to Acceptance Table 1.

Medium: water; 500 mL.

Apparatus 2: 50 rpm.

Times: 1, 2, 4, and 6 hours.

pH 3.0 Buffer solution— Add 6.6 g of ammonium sulfate, accurately weighed, to 500 mL of water. Adjust with 1 N sulfuric acid to a pH of 3.0.

Mobile phase— Prepare a filtered and degassed mixture of methanol and pH 3.0 Buffer solution (50:50). Make adjustments if necessary (see System Suitability under Chromatography 621).

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a UV wavelength detector and a 5-mm × 25-cm column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph a Standard solution of USP Diluted Isosorbide Dinitrate RS in the same Medium, and record the chromatograms as directed for Procedure: the tailing factor is not more than 2.5; and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of a filtered portion of the solution under test, and record the chromatograms. Determine the amount of C6H8N2O8 dissolved in comparison with a Standard solution of USP Diluted Isosorbide Dinitrate RS in the same Medium, similarly chromatographed.

Tolerances— The percentages of the labeled amount of C6H8N2O8 dissolved at the times specified conform to Acceptance Table 2.

(Official April 1, 2006)

(Official January 1, 2007)

Buffer solution, Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Prepare as directed in the Assay under Diluted Isosorbide Dinitrate.

Assay preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 12.5 mg of isosorbide dinitrate, to a dry, 50-mL volumetric flask, add about 30 mL of Mobile phase, and shake the mixture by hand immediately, to prevent clumping. If clumping persists, disperse with the aid of sonication, or break the aggregates with a stirring rod, or warm on a steam bath while keeping the flask stoppered, or allow the flask to stand until the clumps dissipate. [NOTE—If clumping still continues, discard the mixture, and instead disperse an accurately weighed test portion in 15 mL of a 1 in 10 dilution of Buffer solution in water by heating on a steam bath for 1 hour with frequent shaking, then add 15 mL of methanol.] Shake for 30 minutes. Add 8.0 mL of Internal standard solution, cool to room temperature, add 8 mL of a 1 in 10 dilution of Buffer solution in water, dilute with Mobile phase to volume, and mix. Pass a portion through a microporous membrane filter.

Procedure— Proceed as directed for Procedure in the Assay under Diluted Isosorbide Dinitrate. Calculate the quantity, in mg, of C6H8N2O8 in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of isosorbide dinitrate from the USP Isosorbide Dinitrate RS taken for the Standard preparation; and RU and RS are the ratios of the peak responses obtained from the Assay preparation and the Standard preparation, respectively.