A: Infrared Absorption á197Kñ:previously dried at 105for 2hours.

B: Ultraviolet Absorption á197Uñ:previously dried at 105for 2hours.The absorbance of the sample at 285nm is between 0.455and 0.495.

Solution A: 0.1%phosphoric acid adjusted with phosphoric acid to a pHof 2.00±0.1.

Solution B— Use acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Diluent A: a mixture of acetonitrile,methylene chloride,and water (48:1:1).

Diluent B: a mixture of acetonitrile and water (1:1).

Standard stock solution— Dissolve an accurately weighed quantity of USP Oxaprozin RSin acetonitrile to obtain a solution having a concentration of about 200µg per mL.

Standard solution— Transfer 5.0mLof Standard stock solutionto a 200-mLvolumetric flask,and dilute with Diluent Ato volume.

Benzil solution: 200µg of benzil per mLin acetonitrile.

Resolution solution— Transfer 5.0mLof Benzil solutionand 5.0mLof Standard stock solutionto a 100-mLvolumetric flask,and dilute with Diluent Ato volume to obtain a solution having known concentrations of about 10µg of each per mL.

Test solution A— [NOTE—Test solution Ais used to monitor all known and unknown impurities,except imidazolic acid and oximide.]Transfer about 100mg of Oxaprozin,accurately weighed,to a 100-mLvolumetric flask;add 2mLof methylene chloride,2mLof water,and 75mLof acetonitrile;and sonicate after each solvent is added.Dilute with acetonitrile to volume.

Test solution B— [NOTE—Test solution Bis used to monitor only imidazolic acid and oximide.]Transfer about 100mg of Oxaprozin,accurately weighed,to a 100-mLvolumetric flask;add 75mLof Diluent Bto dissolve the Oxaprozin;and dilute withDiluent Bto volume.

Chromatographic system(see Chromatography á621ñ)— The liquid chromatograph is equipped with a 238-nm detector and a 4.6-mm ×15-cm column that contains 5-µm packing L7.The flow rate is 1.0mLper minute.The chromatograph is programmed as follows.

Procedure— Inject 20µLof Test solution Aand Test solution Binto the chromatograph,record the chromatogram,and measure the areas for all the peaks.Calculate the percentage of each impurity in the portion of Oxaprozin taken by the formula: in which Fis the relative response factor and is equal to 1.15for the imidazolic acid peak with a relative retention time of 0.14,1.21for any peak with a relative retention time of 0.42,0.91for the oximide peak with a relative retention time of 0.73,0.85for any peak with a relative retention time of 0.84,1.29for any peak with a relative retention time of 1.08,1.46for any peak with a relative retention time of 1.50,and 2.09for any peak with a relative retention time of 1.57;riis the peak response for each impurity;and rsis the sum of the responses of all the peaks:not more than 0.1%of any individual impurity is found,and not more than 0.5%of total impurities is found.[NOTE—The values of Ffor all known impurities except imidazolic acid and oximide were found using Test solution A,and the values of Ffor imidazolic acid and oximide were found using Test solution B.]

Solvent— Use dimethyl sulfoxide.