Medium: water;500mL.

Apparatus 2: 50rpm.

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

pH3.0buffer solution— Add 6.6g of ammonium sulfate,accurately weighed,to 500mLof water.Adjust with 1Nsulfuric acid to a pHof 3.0.

Mobile phase— Prepare a filtered and degassed mixture of methanol and pH3.0buffer solution(50:50).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Chromatographic system (see Chromatography á621ñ)—The liquid chromatograph is equipped with an UVwavelength detector and a 5-mm ×25-cm column that contains packing L1.The flow rate is about 1mLper minute.Chromatograph a Standard solutionof USP Diluted Isosorbide Dinitrate RSin 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 20µL)of a filtered portion of the solution under test,and record the chromatograms.Determine the amount of C6H8N2O8dissolved in comparison with a Standard solutionof USP Diluted Isosorbide Dinitrate RSin the same medium,similarly chromatographed.

Tolerances— The percentages of the labeled amount of C6H8N2O8dissolved at the times specified conform to Acceptance Table 1.

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 dry,50-mLvolumetric flask,add about 30mLof 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 15mLof a 1in 10dilution of Buffer solution in water by heating on a steam bath for 1hour with frequent shaking,then add 15mLof methanol.]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 to volume,and mix.Filter a portion through a microporous membrane 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.