» Nitroglycerin Ointment is Diluted Nitroglycerin in a suitable ointment base. It contains not less than 90.0 percent and not more than 115.0 percent of the labeled amount of nitroglycerin (C3H5N3O9).
Packaging and storage Preserve in tight containers.
Labeling Label multiple-dose containers with a direction to close tightly, immediately after each use.
USP Reference standards 11
Identification The retention time of the major peak obtained from the Assay preparation corresponds to that from the Standard preparation as obtained in the Assay.
Minimum fill 755: meets the requirements.
Homogeneity In the case of single-dose containers, perform the Assay on specimens from each of 10 containers. In the case of multiple-dose containers, perform the Assay on one specimen from the top and one from the bottom of each of 5 containers. Each specimen contains not less than 90.0% and not more than 110.0% of the mean value.
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:
25C(rU / rS)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.
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USP35NF30 Page 4067