Identification—
Transfer a suitable quantity of finely powdered Tablets to a glass-stoppered centrifuge tube. Add 10 mL of sodium hydroxide solution (1 in 250), shake to wet the powder, then add 15 mL of solvent hexane, and again shake. Centrifuge the mixture, and transfer the upper phase to a beaker. Evaporate the solvent, and dry the residue in vacuum over anhydrous calcium chloride at room temperature for 16 hours: the IR absorption spectrum of a suitable solution in chloroform of the residue so obtained exhibits maxima only at the same wavelengths as that of a similar preparation from the residue obtained from
USP Diluted Isosorbide Dinitrate RS.
Dissolution 
711
—
Medium:
water; 1000 mL.
Apparatus 2:
75 rpm.
Time:
45 minutes.
Mobile phase—
Prepare a suitable degassed and filtered mixture of pH 3.0, 0.1
M ammonium sulfate and methanol (50:50). Make adjustments if necessary (see
System Suitability under
Chromatography 621), using sulfuric acid for any necessary pH adjustment.
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 replicate injections of the Standard solution, and record the peak responses as directed for
Procedure: the relative standard deviation is not more than 2.0%, and the tailing factor is not more than 1.5.
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 70% (Q) of the labeled amount of C6H8N2O8 is dissolved in 45 minutes.
Assay—
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. 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 disposable ion-exchange filter.
Procedure—
Proceed as directed for
Procedure in the
Assay under
Diluted Isosorbide Dinitrate. Calculate the quantity, in mg, of C
6H
8N
2O
8 in the portion of Tablets taken by the formula:
50C(RU / RS),
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.
