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: Thin-Layer Chromatographic Identification Test 201—

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.

Diluent: a mixture of acetonitrile and water (43:57).

0.05 M Monobasic potassium phosphate buffer— Dissolve 6.8 g of monobasic potassium phosphate in 950 mL of water, adjust with dilute phosphoric acid or dilute potassium hydroxide solution to a pH of 4.0 ± 0.05, dilute with water to 1 L, and mix.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile, 0.05 M Monobasic potassium phosphate buffer, and tetrahydrofuran (43:57:2). Make adjustments if necessary (see System Suitability under Chromatography 621).

Diclofenac related compound A solution— Dissolve an accurately weighed quantity of USP Diclofenac Related Compound A RS in Diluent, and quantitatively dilute with Diluent to obtain a solution having a known concentration of about 200 µg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Diclofenac Sodium RS in Diluent, and quantitatively dilute with Diluent to obtain a solution having a known concentration of about 200 µg per mL.

System suitability solution— Transfer 10 mL of the Standard preparation and 5 mL of Diclofenac related compound A solution to a 20-mL volumetric flask. Dilute with Diluent to volume, and mix.

Assay preparation— Powder not fewer than 20 Tablets, and transfer an accurately weighed portion of the powder, equivalent to about 100 mg of diclofenac sodium, to a 100-mL volumetric flask, add about 50 mL of Diluent, sonicate for about 15 minutes, then shake by mechanical means for 15 minutes. Add a few drops of methanol to remove the foam, dilute with Diluent to volume, and mix. Transfer 10.0 mL of the supernatant to a 50-mL volumetric flask, dilute with Diluent to volume, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 254-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L1. The flow rate is about 1.5 mL per minute. Inject 40 µL of the System suitability solution into the chromatograph, and record the peak responses as directed for Procedure: the relative retention times are about 0.9 for diclofenac related compound A and 1.0 for diclofenac; and the resolution, R, between the diclofenac peak and the diclofenac related compound A peak is not less than 2.0. Inject 20 µL of the Standard preparation into the chromatograph, and record the peak responses as directed for Procedure: the tailing factor of the diclofenac peak is not more than 2.0; and the relative standard deviation of the diclofenac peak for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 20 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the area responses for the major peaks. Calculate the quantity, in mg, of diclofenac sodium (C14H10Cl2NNaO2) in the portion of Tablets taken by the formula: in which C is the concentration, in mg per mL, of USP Diclofenac Sodium RS in the Standard preparation; and rU and rS are the diclofenac peak responses obtained from the Assay preparation and the Standard preparation, respectively.