Test solution: 20mg 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 Solventcontaining 600µg per mL.

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

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

Diluted test solution— Quantitatively dilute 1mLof the Test solutionwith Solventto obtain a solution having a concentration of 40µg 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 10µLeach of Standard solution 1,Standard solution 2,the Test solution,and the Diluted test solutionto a thin-layer chromatographic plate (see Thin Layer Chromatography under Chromatography á621ñ)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 105for 5minutes,and examine the plate:any secondary spot in the chromatogram of the Test solutionhaving the same RFvalue as the principal spot from Standard solution 1is not greater in size or intensity than that obtained from Standard solution 1.No secondary spot observed in the chromatogram of the Test solutionhaving the same RFvalue as the principal spot from Standard solution 2is greater in size or intensity than that obtained from Standard solution 2.No other secondary spot observed in the chromatogram of the Test Solutionis greater in size or intensity than the principal spot obtained from the Diluted test solution:not more than 0.1%is found.

Mobile phase— Prepare a filtered and degassed mixture of acetonitrile and water (55:45).Adjust with 0.6Mphosphoric acid to a pHof 3.0.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

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

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

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

Chromatographic system(see Chromatography á621ñ)— 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 1.0mLper 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 0.74for ursodiol and 1.0for 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 50µL)of the Standard preparationand the Assay preparationinto the chromatograph,record the chromatograms,and measure the responses for the major peaks.Calculate the quantity,in mg,of C24H40O4in the portion of Ursodiol taken by the formula: in which Cis the concentration,in mg per mL,of USP Ursodiol RSin the Standard preparation;and RUand RSare the ratios of the ursodiol peak to the internal standard peak obtained from the Assay preparationand the Standard preparation,respectively.