A: Infrared Absorption á197Kñ.

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

Buffer solution,Mobile phase, and Chromatographic system—Proceed as directed in the Assay.

Standard solution— Dissolve an accurately weighed quantity of USP Mefenamic Acid RSin Mobile phaseto obtain a solution having a known concentration of about 10µg per mL.

Test solution— Transfer about 100mg of Mefenamic Acid,accurately weighed,to a 100-mLvolumetric flask,dissolve in and dilute with Mobile phaseto volume,and mix.

Procedure— Separately inject equal volumes (about 10µL)of the Standard solutionand the Test solutioninto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the percentage of each impurity in the portion of Mefenamic Acid taken by the formula: in which CSis the concentration,in µg per mL,of USP Mefenamic Acid RSin the Standard solution;CUis the concentration,in µg per mL,of Mefenamic Acid in the Test solution;riis the peak response for each impurity obtained from the Test solution;and rSis the peak response for mefenamic acid obtained from the Standard solution:not more than 0.1%of any individual impurity is found;and not more than 0.5%of total impurities is found.

Buffer solution— Prepare a 50mMsolution of monobasic ammonium phosphate,and adjust with 3Mammonium hydroxide to a pHof 5.0.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile,Buffer solution,and tetrahydrofuran (23:20:7).Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard preparation— Dissolve an accurately weighed quantity of USP Mefenamic Acid RSin Mobile phase,and dilute quantitatively,and stepwise if necessary,with Mobile phaseto obtain a solution having a known concentration of about 0.2mg per mL.

Assay preparation— Transfer about 100mg of Mefenamic Acid,accurately weighed,to a 500-mLvolumetric flask,dissolve in and dilute with Mobile phaseto 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 that contains packing L1.The flow rate is about 1mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the column efficiency is not less than 8200theoretical plates;the tailing factor for the analyte peak is not more than 1.6;and the relative standard deviation for replicate injections is not more than 1.0%.

Procedure— Separately inject equal volumes (about 10µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C15H15NO2in the portion of Mefenamic Acid taken by the formula: in which Cis the concentration,in mg per mL,of USP Mefenamic Acid RSin the Standard preparation;and rUand rSare the mefenamic acid peak responses obtained from the Assay preparationand the Standard preparation,respectively.