(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 Chewable 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. Filter 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 Chewable 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.