Medium: water;900mL.

Apparatus 2: 50rpm.

Time: 20minutes.

Mobile phase— Prepare a suitable degassed and filtered mixture of pH3.0,0.1Mammonium sulfate and methanol (50:50).

Chromatographic system (see Chromatography á621ñ)—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 1.0mLper 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 20µL)of the Standard solutionand 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 C6H8N2O8dissolved in comparison with a Standard solutionhaving a known concentration of USP Isosorbide Dinitrate RS,similarly prepared and chromatographed.

Tolerances— Not less than 80%(Q)of the labeled amount of C6H8N2O8is dissolved in 20minutes.

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

Assay preparation— Weigh and finely powder not fewer than 20Tablets.Transfer an accurately weighed portion of the powder,equivalent to about 12.5mg of isosorbide dinitrate,to a 50-mLvolumetric flask,add about 30mLof Mobile phase,and shake for 30minutes.Add 8.0mLof Internal standard solution,cool to room temperature,add 8mLof a 1in 10dilution of Buffer solutionin water,dilute with Mobile phaseto volume,and mix.Filter a portion through a 0.45-µm filter.

Procedure— Proceed as directed for Procedurein the Assayunder Diluted Isosorbide Dinitrate.Calculate the quantity,in mg,of C6H8N2O8in the portion of Tablets taken by the formula: in which Cis the concentration,in mg per mL,of isosorbide dinitrate from the USP Isosorbide Dinitrate RStaken for the Standard preparation,and RUand RSare the ratios of the peak responses obtained from the Assay preparationand the Standard preparation,respectively.