Medium: pH 6.8 phosphate buffer (see under Buffer Solutions in the section Reagents, Indicators, and Solutions); 900 mL.

Apparatus 1: 100 rpm.

Time: 45 minutes.

Procedure— Determine the amount of C23H20N2O3S dissolved from UV absorbances at the wavelength of maximum absorbance at about 259 nm of filtered portions of the solution under test, suitably diluted with Dissolution Medium, in comparison with a Standard solution having a known concentration of USP Sulfinpyrazone RS in the same Medium.

Tolerances— Not less than 75% (Q) of the labeled amount of C23H20N2O3S is dissolved in 45 minutes.

Acetonitrile and tetrahydrofuran mixture— Prepare a mixture of acetonitrile and tetrahydrofuran (4:1).

Mobile phase— Prepare a degassed and filtered solution of dilute phosphoric acid (3 in 1000) and Acetonitrile and tetrahydrofuran mixture (65:35).

Internal standard solution— Prepare a solution of Benzoic Acid in acetonitrile having a concentration of about 2 mg per mL.

Standard preparation— Transfer about 100 mg, accurately weighed, of USP Sulfinpyrazone RS to a 200-mL volumetric flask, add 100 mL of acetonitrile, mix, add 10.0 mL of Internal standard solution, dilute with acetonitrile to volume, and mix. Filter, discarding the first 5 mL of the filtrate.

Assay preparation— Remove as completely as possible, and weigh, the contents of not less than 20 Capsules, and mix. Transfer an accurately weighed portion of the powder, equivalent to about 100 mg of sulfinpyrazone, to a 200-mL volumetric flask, add 100 mL of acetonitrile, mix, add 10.0 mL of Internal standard solution, dilute with acetonitrile to volume, and mix. Filter, discarding the first 5 mL of the filtrate.

Chromatographic system (see Chromatography 621)—The liquid chromatograph is equipped with a 235-nm detector and a 4.6-mm × 10-cm column that contains packing L1. The flow rate is about 3 mL per minute. Chromatograph the Standard preparation, and record the peak responses as directed under Procedure: the relative retention times are about 0.2 for benzoic acid and 1.0 for sulfinpyrazone; the resolution, R, between benzoic acid and sulfinpyrazone is not less than 13; and the relative standard deviation is not more than 2.0%.

Procedure— Separately inject equal volumes (about 10 µL) of the Standard preparation and the Assay preparation into the chromatograph, record the chromatograms, and measure the responses for the major peaks. The resolution, R, between benzoic acid and sulfinpyrazone is not less than 13. Calculate the quantity, in mg, of C23H20N2O3S in the portion of Capsule contents taken by the formula: in which C is the concentration, in mg per mL, of USP Sulfinpyrazone RS in the Standard preparation, and RU and RS are the relative peak response ratios obtained from the Assay preparation and the Standard preparation, respectively.