Test solution: 20 mg per mL, in alcohol.

Adsorbent: 0.25-mm layer of chromatographic silica gel.

Solvent— Prepare a mixture of acetone and water (9:1).

Standard solution 1— Prepare a solution of chenodiol in Solvent containing 600 µg per mL.

Standard solution 2— Prepare a solution of lithocholic acid in Solvent containing 20 µg per mL.

Test solution— Prepare a solution of Ursodiol in Solvent containing 40 mg per mL.

Diluted test solution— Quantitatively dilute 1 mL of the Test solution with Solvent to obtain a solution having a concentration of 40 µg per mL.

Developing solvent system: a mixture of chloroform, glacial acetic acid, and water (85:15:0.5)

Spray reagent: phosphomolybdic acid TS.

Procedure— Separately apply 10 µL each of Standard solution 1, Standard solution 2, the Test solution, and the Diluted test solution to a thin-layer chromatographic plate (see Thin Layer Chromatography under Chromatography 621 ), and proceed as directed in the chapter, allowing the solvent front to move about three-fourths of the length of the plate. Remove the plate from the developing chamber, mark the solvent front, and air-dry the plate. Spray the plate with phosphomolybdic acid TS, dry at 105 for 5 minutes, and examine the plate: any secondary spot in the chromatogram of the Test solution having the same RF value as the principal spot from Standard solution 1 is not greater in size or intensity than that obtained from Standard solution 1: not more than 1.5% of chenodiol is found. No secondary spot observed in the chromatogram of the Test solution having the same RF value as the principal spot from Standard solution 2 is greater in size or intensity than that obtained from Standard solution 2: not more than 0.05% of lithocholic acid is found. No other secondary spot observed in the chromatogram of the Test solution is greater in size or intensity than the principal spot obtained from the Diluted test solution: not more than 0.1% of any other impurity is found.

(Official January 1, 2007)

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (55:45). Adjust with 0.6 M phosphoric acid to a pH of 3.0. Make adjustments if necessary (see System Suitability under Chromatography 621).

Internal standard solution— Dissolve an accurately weighed quantity of epiandrosterone in methanol to obtain a solution having a concentration of about 4 mg per mL. Dilute a portion of this solution quantitatively with Mobile phase to obtain a solution having a concentration of about 0.8 mg per mL.

Standard preparation— Dissolve an accurately weighed quantity of USP Ursodiol RS in methanol, and dilute quantitatively, and stepwise if necessary, with methanol to obtain a solution having a known concentration of about 4 mg per mL. Transfer this solution to a suitable container, and dilute with Mobile phase to give a solution having a known concentration of about 0.8 mg of ursodiol per mL. Transfer equal volumes of this solution and the Internal standard solution to a suitable container, and mix.

Assay preparation— Transfer about 100 mg of Ursodiol, accurately weighed, to a 25-mL volumetric flask, dissolve in and dilute with methanol to volume. Transfer 5.0 mL of this solution to a 25-mL volumetric flask, dilute with Mobile phase to volume, and mix. Transfer equal volumes of this solution and the Internal standard solution to a suitable container, and mix.

Chromatographic system (see Chromatography 621)— The liquid chromatograph is equipped with a differential refractive index detector and a 3.9-mm × 30-cm column that contains packing L1. The flow rate is about 1.0 mL per minute. Both the detector temperature and the column temperature are maintained at 40. Chromatograph the Standard preparation, and record the peak responses as directed for Procedure: the relative retention times are about 0.74 for ursodiol and 1.0 for epiandrosterone; the resolution, R, between ursodiol and epiandrosterone is not less than 3.8 (If the resolution specification is not met, increase the water content of the Mobile phase); and the relative standard deviation for replicate injections is not more than 1.0%.

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 C24H40O4 in the portion of Ursodiol taken by the formula: in which C is the concentration, in mg per mL, of USP Ursodiol RS in the Standard preparation; and R U and R S are the ratios of the ursodiol peak to the internal standard peak obtained from the Assay preparation and the Standard preparation, respectively.