Diclofenac Sodium
(dye kloe' fen ak soe' dee um).
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C14H10Cl2NNaO2 318.13

Benzeneacetic acid, 2-[(2,6-dichlorophenyl)amino]-, monosodium salt.
Sodium [o-(2,6-dichloroanilino)phenyl]acetate [15307-79-6].
» Diclofenac Sodium contains not less than 99.0 percent and not more than 101.0 percent of C14H10Cl2NNaO2, calculated on the dried basis.
Packaging and storage— Preserve in tight, light-resistant containers.
USP Reference standards 11
USP Diclofenac Sodium RS Click to View Structure
USP Diclofenac Related Compound A RS Click to View Structure
    C14H9Cl2NO    278.14
B: The retention time of the diclofenac peak in the chromatogram of the Test solution corresponds to that of the Resolution solution as obtained in the test for Chromatographic purity.
C: The residue obtained by igniting it responds to the flame test for Sodium 191.
Color of solution— A 1 in 20 solution of it in methanol is colorless to faintly yellow, and the absorbance of the solution, determined in a 1-cm cell at 440 nm, is not more than 0.050, methanol being used as the blank.
Clarity of solution— The solution prepared as directed under Color of solution is not significantly less clear than an equal volume of methanol contained in a similar vessel and examined similarly.
pH 791: between 7.0 and 8.5, in a solution (1 in 100).
Loss on drying 731 Dry it at 105 to 110 for 3 hours: it loses not more than 0.5% of its weight.
Heavy metals, Method II 231 To prepare the Test Preparation, use a 100-mL borosilicate glass beaker or a quartz crucible. If the residue is not completely white after the ignition at 500 to 600, add enough hydrogen peroxide to dissolve it, heat gently until dry, and ignite for 1 hour. Repeat the hydrogen peroxide treatment and ignition until the residue is completely white. Proceed as directed in Test Preparation, beginning with “Cool, add 4 mL of 6 N hydrochloric acid.” The limit is 0.001%.
Chromatographic purity—
pH 2.5 Phosphate buffer— Mix equal volumes of 0.01 M phosphoric acid and 0.01 M monobasic sodium phosphate. If necessary, adjust with additional portions of the appropriate component to a pH of 2.5 ± 0.2.
Mobile phase— Prepare a filtered and degassed mixture of methanol and pH 2.5 Phosphate buffer (700:300). Make adjustments if necessary (see System Suitability under Chromatography 621). [note—Increasing the proportion of buffer increases resolution. ]
Diluent— Prepare a mixture of methanol and water (70:30).
Standard solution— Prepare a solution of USP Diclofenac Related Compound A RS in methanol having a known concentration of about 0.75 mg per mL. Quantitatively dilute an accurately measured volume of this stock solution with Diluent to obtain a solution having a known concentration of about 1.5 µg per mL.
Resolution solution— Prepare a solution in Diluent containing 20 µg of diethyl phthalate, 7.5 µg of USP Diclofenac Related Compound A RS, and 0.75 mg of USP Diclofenac Sodium RS per mL.
Test solution— Transfer about 75 mg of Diclofenac Sodium, accurately weighed, to a 100-mL volumetric flask, dissolve in and 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 × 25-cm column containing packing L7 (end-capped). The flow rate is about 1 mL per minute. Chromatograph the Resolution solution, and record the peak responses as directed for Procedure: the relative retention times are about 0.5 for diethyl phthalate, 0.6 for diclofenac related compound A, and 1.0 for diclofenac; and the resolution, R, between diethyl phthalate and diclofenac related compound A is not less than 2.2, and that between diclofenac related compound A and diclofenac is not less than 6.5. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the relative standard deviation for replicate injections is not more than 5%.
Procedure— Separately inject equal volumes (about 10 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the peak responses over a period of 2.5 times the retention time of diclofenac. Calculate the percentage of diclofenac related compound A in the portion of Diclofenac Sodium taken by the formula:
10(C / W)(rU / rS)
in which C is the concentration, in µg per mL, of USP Diclofenac Related Compound A RS in the Standard solution; W is the quantity, in mg, of Diclofenac Sodium taken to prepare the Test solution; and rU and rS are the diclofenac related compound A peak responses obtained from the Test solution and the Standard solution, respectively: not more than 0.2% is found. Calculate the percentage of each other impurity in the portion of Diclofenac Sodium taken by the formula:
10(C / W)(ri / rS)
in which ri is the response of an individual impurity peak obtained from the Test solution, and the other terms are as defined above: not more than 0.2% of any individual impurity is found. The sum of all of the impurities found is not more than 0.5%.
Assay— Dissolve about 450 mg of Diclofenac Sodium, accurately weighed, in 25 mL of glacial acetic acid, and titrate with 0.1 N perchloric acid VS, determining the endpoint potentiometrically. Perform a blank determination, and make any necessary correction. Each mL of 0.1 N perchloric acid is equivalent to 31.81 mg of C14H10Cl2NNaO2.
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