Mobile phase, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Diluted Nitroglycerin.

Assay preparation— Transfer an accurately weighed portion of Ointment, equivalent to about 2.0 mg of nitroglycerin, to a glass-stoppered, 50-mL conical flask, and add 25.0 mL of Mobile phase. Immerse for 10 minutes in a water bath maintained at a temperature of 50, shaking intermittently until the specimen becomes dispersed. Remove from the bath, and shake vigorously for 1 minute to obtain a coagulated solid. Repeat the heating and shaking steps one more time and filter.

Procedure— Separately inject equal volumes of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the quantity, in mg, of C3H5N3O9 in the portion of Ointment taken by the formula: in which C is the concentration, in mg per mL, of nitroglycerin in the Standard preparation, and rU and rS are the peak responses of nitroglycerin obtained from the Assay preparation and the Standard preparation, respectively.