A:Infrared Absorption á197Kñ.

B:Ultraviolet Absorption á197Uñ—

Diluent— Prepare a mixture of water and dehydrated alcohol (1:1).

Butylparaben solution— Transfer about 25mg of butylparaben to a 100-mLvolumetric flask,dilute with Diluentto volume,and mix

Solution A— Use filtered and degassed water.

Solution B— Use filtered and degassed acetonitrile.

Mobile phase— Use variable mixtures of Solution Aand Solution Bas directed for Chromatographic system.Make adjustments if necessary (see System Suitabilityunder Chromatography á621ñ).

Standard solution— Dilute USP Paricalcitol Solution RSin Diluent to a known concentration of about 0.1µg of paricalcitol per mL.

Control standard solution— Transfer 3.0mLof the Standard solutionto a 10.0-mLvolumetric flask,dilute with Diluentto volume,and mix.

Test stock solution— Transfer about 10mg of Paricalcitol,accurately weighed,to a 50-mLvolumetric flask,dissolve in and dilute with dehydrated alcohol to volume,and mix.

Resolution solution— Transfer 1mLof the Butylparaben solutionand 1mLof the Test stock solutionto a 100-mLvolumetric flask,dilute with Diluentto volume,and mix.Transfer 1mLof this solution to a 10-mLvolumetric flask,dilute with Diluentto volume,and mix.

Test solution— Prepare a mixture of the Test stock solutionand water (1:1).

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 252-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 2mLper minute.The chromatograph is programmed as follows. Chromatograph the Resolution solution,and record the peak responses as directed for Procedure:the resolution,R,between paricalcitol and butylparaben is not less than 12.0.Chromatograph the Standard solutionand the Control standard solution,and record the peak responses as directed for Procedure:the area ratio for the paricalcitol peak from the Standard solutionto that from the Control standard solutionis between 1.8and 4.0;and the relative standard deviation for replicate injections of the Standard solutionis not more than 10.0%.

Procedure— Separately inject equal volumes (about 100µL)of the Diluent,the Standard solution,and the Test solutioninto the chromatograph,record the chromatograms,and measure the peak responses,disregarding any peaks corresponding to those obtained from the Diluent.Calculate the percentage of each impurity in the portion of Paricalcitol taken by the formula: in which Cis the concentration,in µg per mL,of USP Paricalcitol RSin the Standard solution;Wis the weight,in mg,of Paricalcitol taken to prepare the Test stock solution;riis the peak response for each impurity obtained from the Test solution;and rSis the paricalcitol peak response obtained from the Standard solution:not more than 0.1%of any individual impurity is found;and not more than 0.5%of total impurities is found.

Mobile phase— Prepare a filtered and degassed mixture of methanol and water (4:1).Make adjustments if necessary (see System Suitability under Chromatography á621ñ).

Diluent— Prepare a mixture of methanol and water (1:1).

Standard preparation— Prepare a solution of USP Paricalcitol RSin dehydrated alcohol having a known concentration of about 0.5mg per mL.Dilute this solution quantitatively,and stepwise if necessary,with Diluentto obtain a solution having a known concentration of about 5.0µg per mL.

Assay preparation— Transfer about 25mg of Paricalcitol,accurately weighed,to a 50-mLlow actinic volumetric flask,dissolve in and dilute with dehydrated alcohol to volume,and mix.Transfer 2.0mLof this solution to a 200-mLvolumetric flask,dilute with Diluentto volume,and mix.

Chromatographic system (see Chromatography á621ñ)— The liquid chromatograph is equipped with a 252-nm detector and a 4.6-mm ×25-cm column that contains 5-µm packing L1.The flow rate is about 2mLper minute.Chromatograph the Standard preparation,and record the peak responses as directed for Procedure:the tailing factor is not more than 2.0;and the relative standard deviation for replicate injections is not more than 2.0%.

Procedure— Separately inject equal volumes (about 100µL)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 C27H44O3in the portion of Paricalcitol taken by the formula: in which Cis the concentration,in µg per mL,of USP Paricalcitol RSin the Standard preparation;and rUand rSare the paricalcitol peak responses obtained from the Assay preparationand the Standard preparation,respectively.