Medium: water; 900 mL.

Apparatus 2: 50 rpm.

Time: 20 minutes.

Mobile phase— Prepare a suitable degassed and filtered mixture of pH 3.0, 0.1 M ammonium sulfate and methanol (50:50).

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 220-nm detector and a 4.6-mm × 5-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. Chromatograph the Standard solution, and record the peak responses as directed under Procedure: the tailing factor is not more than 1.5, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard solution and a filtered aliquot of the solution under test into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the amount of C6H8N2O8 dissolved in comparison with a Standard solution having a known concentration of USP Isosorbide Dinitrate RS, similarly prepared and chromatographed.

Tolerances— Not less than 80% (Q) of the labeled amount of C6H8N2O8 is dissolved in 20 minutes.

(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 50-mL volumetric flask, add about 30 mL of Mobile phase, and 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 0.45-µm 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.