note—Nifedipine, when exposed to daylight and certain wavelengths of artificial light, readily converts to a nitrosophenylpyridine derivative. Exposure to UV light leads to the formation of a nitrophenylpyridine derivative. Perform assays and tests in the dark or under golden fluorescent or other low-actinic light. Use low-actinic glassware.

A: The retention time of the major peak in the chromatogram of the Assay preparation corresponds to that in the chromatogram of the Standard preparation, as obtained in the Assay.

B: Ultraviolet Absorption 197U—

test 1— If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 1.

test 2— If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 2.

test 3— If the product complies with this test, the labeling indicates that it meets USP Dissolution Test 3.

test 4— If the product complies with this test, the labeling indicates that the product meets USP Dissolution Test 4.

test 5— If the product complies with this test, the labeling indicates that the product meets USP Dissolution Test 5.

Mobile phase— Prepare as directed in the Assay under Nifedipine.

Standard nifedipine solution, Reference solution 1, and Reference solution 2— Prepare as directed in the test for Related compounds under Nifedipine, except to obtain solutions having known concentrations of about 6 µg per mL and 1.5 µg per mL for Reference solution 1 and Reference solution 2, respectively.

System suitability solution— Mix equal volumes of the Standard nifedipine solution, Reference solution 1, and Reference solution 2.

Standard solution— Transfer 5.0 mL of each Reference solution to a container, add 5.0 mL of Mobile phase, and mix. Each mL of this solution contains about 2 µg of USP Nifedipine Nitrophenylpyridine Analog RS and 0.5 µg of USP Nifedipine Nitrosophenylpyridine Analog RS.

Test solution— Use a portion of the Assay preparation.

Chromatographic system (see Chromatography 621)— Prepare as directed in the Assay. Chromatograph the System suitability solution, and record the peak responses as directed for Procedure: the resolution, R, between nitrophenylpyridine analog and nitrosophenylpyridine analog is not less than 1.5; the resolution, R, between nitrosophenylpyridine analog and nifedipine is not less than 1.0; and for each analog, the relative standard deviation for replicate injections is not more than 10%.

Procedure— Separately inject equal volumes (about 25 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of each related compound in the portion of Tablets taken by the formula: in which C is the concentration, in µg per mL, of the appropriate analog USP Reference Standard in the Standard solution; W is the weight, in mg, of nifedipine in the Tablets taken to prepare the Test solution; and ri and rS are the peak responses of the corresponding related compound obtained from the Test solution and the Standard solution, respectively: not more than 2.0% of nifedipine nitrophenylpyridine analog and not more than 0.5% of nifedipine nitrosophenylpyridine analog, both relative to the nifedipine content, are found.

Mobile phase and Standard preparation— Prepare as directed in the Assay under Nifedipine.

Assay preparation— Select a number of Tablets, equivalent to about 420 mg of nifedipine. Finely powder the Tablets, and transfer the powder to a 250-mL volumetric flask containing 130 mL of water; or transfer the intact Tablets to a 400-mL, high-speed blender cup containing 130 mL of water, homogenize until a uniform suspension is achieved (about 2 minutes), and transfer the suspension with the aid of a mixture of acetonitrile and methanol (1:1) to a 250-mL volumetric flask. Add a mixture of acetonitrile and methanol (1:1) to volume, and stir for 30 minutes. Centrifuge the resulting suspension to obtain a clear supernatant stock solution. Transfer 3.0 mL of the stock solution to a 50-mL volumetric flask, dilute with Mobile phase to volume, mix, and filter to obtain a solution having a concentration of about 0.1 mg of nifedipine per mL. [note—Reserve a portion of this Assay preparation for use as the Test solution in the test for Related compounds.]

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 265-nm detector, a 4.6-mm × 25-cm analytical column that contains packing L1, and a 2.1-mm × 3-cm guard column that contains packing L1. The flow rate is about 1 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 4000 theoretical plates; the tailing factor is not more than 1.5; and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 25 µL) 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 nifedipine (C17H18N2O6) in the Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Nifedipine RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.