A: Infrared Absorption á197Kñ.

B: The retention time of the diclofenac peak in the chromatogram of the Test solutioncorresponds to that of the Resolution solutionas obtained in the test for Chromatographic purity.

C: The residue obtained by igniting it responds to the flame test for Sodium á191ñ.

A: The solution prepared as directed under Color of solutionis not significantly less clear than an equal volume of methanol contained in a similar vessel and examined similarly.

pH2.5Phosphate buffer— Mix equal volumes of 0.01Mphosphoric acid and 0.01Mmonobasic sodium phosphate.If necessary,adjust with additional portions of the appropriate component to a pHof 2.5±0.2.

Mobile phase— Prepare a filtered and degassed mixture of methanol and pH2.5Phosphate buffer(700:300).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).[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 RSin methanol having a known concentration of about 0.75mg per mL.Quantitatively dilute an accurately measured volume of this stock solution with Diluentto obtain a solution having a known concentration of about 1.5µg per mL.

Resolution solution— Prepare a solution in Diluentcontaining 20µg of diethyl phthalate,7.5µg of USP Diclofenac Related Compound A RS,and 0.75mg of USP Diclofenac Sodium RSper mL.

Test solution— Transfer about 75mg of Diclofenac Sodium,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Diluentto volume,and mix.

Chromatographic system (see Chromatography á621ñ)—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 1mLper minute.Chromatograph the Resolution solution,and record the peak responses as directed under Procedure:the relative retention times are about 0.5for diethyl phthalate,0.6for diclofenac related compound A,and 1.0for diclofenac;and the resolution,R,between diethyl phthalate and diclofenac related compound Ais not less than 2.2,and between diclofenac related compound Aand diclofenac is not less than 6.5.Chromatograph the Standard solution,and record the peak responses as directed under Procedure:the relative standard deviation for replicate injections is not more than 5%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses over a period of 2.5times the retention time of diclofenac.Calculate the percentage of diclofenac related compound Ain the Diclofenac Sodium taken by the formula: in which Cis the concentration,in µg per mL,of USP Diclofenac Related Compound A RSin the Standard solution;Wis the quantity,in mg,of Diclofenac Sodium taken to prepare the Test solution;and rUand rSare the diclofenac related compound Apeak responses obtained from the Test solutionand the Standard solution,respectively:not more than 0.2%is found.Calculate the percentage of each other impurity in the Diclofenac Sodium taken by the formula: in which riis 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%.