A: Thin-Layer Chromatographic Identification Test 201—

B: 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.

Medium: 0.05 M monobasic potassium phosphate buffer, pH 7.4; 1000 mL.

Apparatus 2: 75 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C18H15NO3 dissolved by employing UV absorption at the wavelength of maximum absorbance at about 286 nm on filtered portions of the solution under test, suitably diluted with Dissolution Medium, if necessary, in comparison with a Standard solution having a known concentration of USP Oxaprozin RS in the same Medium (an amount of methanol not exceeding 5% of the final volume can be added to help solubilize the USP Reference Standard).

Tolerances— Not less than 75% (Q) of the labeled amount of C18H15NO3 is dissolved in 45 minutes.

0.1% Phosphoric acid, pH 2.00 ± 0.10— Add concentrated phosphoric acid, dropwise, to water to obtain a pH of 2.00 ± 0.10.

Mobile phase— Prepare a filtered and degassed solution of 0.1% Phosphoric acid, pH 2.00 ± 0.10 and acetonitrile (55:45).

Standard preparation— Dissolve an accurately weighed quantity of USP Oxaprozin RS in acetonitrile to obtain a solution having a concentration of about 12 µg of oxaprozin per mL.

Assay stock preparation— Weigh and finely powder not fewer than 20 Tablets. Transfer an accurately weighed portion of the powder, equivalent to about 60 mg of oxaprozin, to a 100-mL volumetric flask, add about 10 mL of water, and sonicate for 10 minutes. Add about 40 mL of acetonitrile, sonicate for 30 minutes, shake by mechanical means for an additional 30 minutes, add about 30 mL of acetonitrile, and sonicate for 10 minutes. Dilute with acetonitrile to volume.

Assay preparation— Quantitatively dilute the Assay stock preparation with acetonitrile to obtain a solution having a concentration of about 12 µg of oxaprozin per mL.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a 285-nm detector and a 4.6-mm × 15-cm column that contains 5-µm packing L7. The flow rate is about 1.0 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the tailing factor is not more than 2.0; and the relative standard deviation 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 responses for the major peaks. Calculate the quantity, in mg, of oxaprozin (C18H15NO3) in the portion of Tablets taken by the formula: in which C is the concentration in mg per mL of USP Oxaprozin RS in the Standard preparation; and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.