A: Infrared Absorption 197M—Do not dry specimens.

B: Ultraviolet Absorption 197U—

Solution: 10 µg per mL.

Medium: hydrochloric acid in methanol (1 in 1200).

C: Prepare a test solution of it in a mixture of chloroform and methanol (1:1) containing 1 mg per mL. Similarly prepare a Standard solution, using USP Piroxicam RS. Separately apply 20-µL portions of the test solution and the Standard solution to a suitable thin-layer chromatographic plate (see Chromatography 621) coated with a 0.25-mm layer of chromatographic silica gel. Allow the spots to dry, and develop the chromatogram in a solvent system consisting of a mixture of toluene and glacial acetic acid (95:5) until the solvent front has moved about three-fourths of the length of the plate. Remove the plate from the developing chamber, and air-dry. Place the plate in the developing chamber, and develop as before. Remove the plate from the chamber, mark the solvent front, and air-dry. Locate the spots on the plate by viewing under short-wavelength UV light: the RF value of the principal spot obtained from the test solution corresponds to that obtained from the Standard solution.

Solvent— Use dimethyl sulfoxide.

(Official January 1, 2007)

Buffer— Dissolve 7.72 g of anhydrous citric acid in 400 mL of water, and separately dissolve 5.35 g of dibasic sodium phosphate in 100 mL of water. Add the phosphate solution to the citric acid solution, dilute with water to make 1000 mL, and mix.

Mobile phase— Prepare a suitable mixture of Buffer and methanol (55:45), and degas.

Standard preparation— Dissolve an accurately weighed quantity of USP Piroxicam RS in 0.01 N methanolic hydrochloric acid to obtain a solution having a known concentration of about 0.25 mg per mL. Transfer 10.0 mL of this solution to a 50-mL volumetric flask, add about 25 mL of 0.01 N methanolic hydrochloric acid and 10.0 mL of water, dilute with 0.01 N methanolic hydrochloric acid to volume, and mix. This solution contains about 0.05 mg per mL.

Assay preparation— Transfer about 50 mg of Piroxicam, accurately weighed, to a 100-mL volumetric flask, dilute with 0.01 N methanolic hydrochloric acid to volume, and mix. Transfer 10.0 mL of this solution to a second 100-mL volumetric flask, add about 50 mL of 0.01 N methanolic hydrochloric acid and 20.0 mL of water, dilute with 0.01 N methanolic hydrochloric acid to volume, and mix.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 254-nm detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.2 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the column efficiency is not less than 500 theoretical plates, the tailing factor is not more than 1.5, and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 25 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 C15H13N3O4S in the portion of Piroxicam taken by the formula: in which C is the concentration, in mg per mL, of USP Piroxicam RS in the Standard preparation, and rU and rS are the peak responses obtained from the Assay preparation and the Standard preparation, respectively.