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Medium: 0.5 MUSP29 pH 8.4 phosphate buffer, prepared by mixing 250 mL of 0.2 M monobasic potassium phosphate, 280 mL of 0.2 M potassium hydroxide, and 5 mL of 2% sodium lauryl sulfate solution. Adjust with 0.2 M potassium hydroxide to a pH of 8.4, and dilute with water to 1000 mL; 1000 mL.

Apparatus 2: 75 rpm.

Time: 30 minutes.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and 0.075 M monobasic potassium phosphate (50:50). Adjust with 85% phosphoric acid to a pH of 3.0. Make adjustments if necessary (see System Suitability under Chromatography 621).

Standard solution— Dissolve an accurately weighed quantity of USP Ursodiol RS, and dilute quantitatively, and stepwise if necessary, with Medium to obtain a solution having a known concentration equivalent to that expected in the solution under test.

Test solution— Use a filtered portion of the solution under test.

Chromatographic system— The liquid chromatograph is equipped with a refractive index detector, a guard column that contains packing L1, and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1 mL per minute, and the column and detector temperatures are maintained at 40. Chromatograph the Standard solution, and record the peak responses as directed for Procedure: the tailing factor of the ursodiol peak is not more than 1.7; and the relative standard deviation for replicate injections is not more than 2%.

Procedure— Separately inject equal volumes (about 50 µL) of the Standard solution and the Test solution into the chromatograph, record the chromatograms, and measure the responses for the major peaks. Calculate the percentage of C24H40O4 dissolved by the formula: in which rU and rS are the peak responses obtained from the Test solution and the Standard solution, respectively; C is the concentration, in mg per mL, of USP Ursodiol RS in the Standard solution; and W is the labeled amount, in mg, of ursodiol in each Capsule.

Tolerances— Not less than 80% (Q) of the labeled amount of C24H40O4 is dissolved in 30 minutes.

(Official January 1, 2007)

Mobile phase, Internal standard solution, Standard preparation, and Chromatographic system— Proceed as directed in the Assay under Ursodiol.

Assay preparation— Accurately weigh the contents of not fewer than 20 Capsules, and mix. Transfer an accurately weighed portion of the powder, equivalent to about 200 mg of ursodiol, to a 50-mL volumetric flask. Add about 40 mL of methanol, and sonicate for about 15 minutes. Cool the mixture to room temperature, dilute with methanol to volume, and centrifuge a portion of this mixture. Transfer 5.0 mL of the clear supernatant to a 25-mL volumetric flask, and dilute with Mobile phase to volume. Transfer equal amounts of this solution and the Internal standard solution to a suitable container, mix, and filter.

Procedure— Separately inject equal volumes (about 50 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 ursodiol (C24H40O4) in the portion of Capsules taken by the formula: in which CS and CU are the concentrations, in mg per mL, of ursodiol in the Standard preparation and the Assay preparation, respectively; and RU and RS are the ratios of the ursodiol peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.